Abstract
Internationalization is a theme of great interest to practitioners worldwide, intensified by the increasing business environmental turbulence in last decades. The latter led to the proliferation and expanding of research into new areas, while neoclassic archetypes were conversely dubbed as, supposedly “old-fashioned.” In this context, a review article aims at breaking with such dogma, rejuvenating prior knowledge, and contextualizing it in current time. Hence, this research focus on a seminal framework, the well-known Uppsala Model, purposively selected as being an exception, as it keeps capturing the interest of scholars and is still one of the most cited frameworks in this area. Thus, a theoretical review addresses the evolution of the model in the aftermath of more than 40 years of research, and contextualizes it within the state-of-the-art of internationalization-related theories. An integrative review process is applied to a purposeful selection of descending frameworks of the model, circumscribed to the last decade (2009–2019). An enduring utility is positively observed, grounded on a reactive adaption purpose. In parallel, a shift is assisted from the neoclassic paradigm to a behavioral paradigm pillared on a capability-building logic for the adaption toward volatile, uncertain, complex, and ambiguous environments. This led to the extension of the Uppsala paradigm from a pure internationalization process model to enter the realm of the international capabilization framework.
Introduction
Changes in the business ecosystems influence significantly the microsphere of the firms’ actions (Coviello et al., 2017). Thus, aware of the impact of the environment on a firm’s strategic options, and furthermore, paving the way for the extension of academic research, this article focuses on Neoclassic Theory, within the field of international business (IB) to grasp its longevity and utility and break with the dogma of Neoclassicism as a synonym of superannuation (Welch et al., 2016). The Uppsala Internationalization Model is here instrumentalized, due to the continuous criticism that it has collected since its foundation; nonetheless, being one of the frameworks that garners most attention within the internationalization context (Pukall & Calabrò, 2014; Welch et al., 2016).
The opposition to Uppsala seems to derive from the emergence of further conceptions which have defied its rationale, since the novelty brought by the theoretical advancements could allegedly replace the role originally played by the Uppsala Model as an internationalization process model (Johanson & Vahlne, 1977). Such an assumption seems to have given space for the flourishing of a growing opposition, deriving from the effective enlargement of the body of theory in the last decades. This constitutes, therefore, the lever for the formulation of an initial problem statement: Depreciation of neoclassic theory (U-model) on the presence of contemporary frameworks with equivalent purpose and higher alleged functionality.
With abundance of alternative frameworks and recurrent antagonism, this research seeks further comprehension of the suitability of the Uppsala Model to adjust to current business ecosystems in the light of increasing volatility, uncertainty, complexity, and ambiguity (VUCA) (Bennett & Lemoine, 2014a, 2014b). In this sense, the investigation focus in understanding whether the case-model holds the ability to endure its time horizon to the present (Aim 1) and to endure its utility (Aim 2), adapting to these two categories of challenges (scientific environment advancement). Thus, the aims above were the baseline for the launching of the following research question (RQ): How does the U-model endure?
With the purpose of providing a clear answer to this question, a theoretical review of the literature is hereby undertaken and it focuses on the model termed as the “1977 model,” the “Uppsala Model,” or “U-model”; and moreover, on its foundation, and on the further theorizations (the “descending models”) released by the Uppsala University and their co-research partnering institutions/followers, to describe the evolution of the rationale to present, crosschecked with the main contemporary theorizations in the field to attest the current relevance of the Uppsala paradigm; and ultimately respond to the above research question.
The review of the literature is pillared on a methodological ground of an integrative review process, in which the reviewed literature is classified by means of a dyad of processes (i.e., the process of discovery and the process of justification) (MacInnis, 2011, p. 136). This methodological procedure is disclosed below in the “Method and Research Framework” section and demonstrated in “Results and discussion” section, allowing the fashion of a chronological analysis of the sequence of evolution occurred in the last decade (2009–2019).
Literature Review and Theory Development
Origins and Morphology
Within the IB field, researchers from the University of Uppsala fashioned in the 1970s a behavioral-based internationalization model focused on empirical observations from the Swedish firm’s experience abroad (Johanson & Vahlne, 1977; Johanson & Wiedersheim-Paul, 1975). The model prescribed a process of internationalization based on the perceived risks and uncertainty of foreign markets. The model posited a low-paced commitment with a sequential order to mitigate risk. Market knowledge is at the epicenter of the risk/uncertainty control, in which the higher the firm knowledge possessed the less it would be the uncertainty surrounding the recovery of a direct investment abroad.
Such an approach had on its etymology the researchers’ assumption that markets are distinct, and the set of dissimilar characteristics between home and foreign countries could be acknowledged and interpreted at different stages of the internationalization process: ex ante (pre-entry phase); ongoing and in locus (during the establishment phase); and ex post (post-entry phase). The distinctiveness of domestic versus host-market attributes constituted a perceived gap designated as psychic distance (PD) determining market-entry decisions (Nordman & Tolstoy, 2014; Safari & Chetty, 2019). Markets of higher PD were subsequently perceived as markets of higher uncertainty and consequently less attractive (Håkanson & Ambos, 2010). The model asserted that international venturing ought to start on the surrounding familiar markets and gradually extend operations to distant and more unfamiliar ones such as the four initially tested companies (Sandvik, Atlas Copco, Facit, and Volvo; Johanson & Wiedersheim-Paul, 1975).
This PD phenomenon unfolded through two main categories (cultural and business), accounting PD factors, such as language, education, business practices, cultural norms, and industrial development; political systems, communications systems, trade and other social exchange; and/or prior knowledge about laws or rules (J. Johanson & Vahlne, 1977, 2009).The level of involvement would vary according to the outcomes of perceptual distance due to the cross-interaction of those aforementioned PD factors. Here, a system of relations between variables, commitment (C), perceived risk (R), and uncertainty (U), explained the firm’s commitment decisions, and drawn an imaginary boundary line determining the “maximum tolerable market risk” (R*), to support market-entry and further investment decisions (J. Johanson & Vahlne, 1977).
Obstacles, Antagonism, and Theoretical Advancement
From the original U-model, is deduced a second assumption of superior performance deriving from the selection of markets of psychic closeness. Nevertheless, several are the empirical evidence that deconstruct such a belief, unifying what is termed of a PD paradox (Evans & Mavondo, 2002; Magnusson et al., 2014; O’Grady & Lane, 1996). This latter refers to the apparent ease of doing business in short PD markets, due to the similarities between the two countries, which may trigger the complacency or even the inertia of the internationalizer to adapt to fewer or subtler environment differences, which in turn may drive to failure.
In this sense, the PD paradox emphasizes the key role of market knowledge in the organizational performance overseas, as regardless of the geographical diversification (inter or intra-regional) experiential knowledge regulates the surplus of costs (i.e., the liability of foreignness) that limit the fruition of higher economic rents and constitute a competitive disadvantage against local firms (Petersen & Pedersen, 2002; Qian et al., 2013; Zaheer, 1995). These costs are originated from spatial distance, unfamiliarity with the local environment; and home/host-country costs. Thus, involvement with local stakeholders, and subsequent adaptation to local requirements and organizational practices is essential for deepening experiential knowledge. Hence, Zaheer (1995) argues that MNEs frequently establish complacent positions of simply copy local practices, to avoid rejection or failure, as the liability of outsidership, that is, “the lack of such market-specific business knowledge” as “the” challenge to be fulfilled in the host-markets of effective investment (Johanson & Vahlne, 2009, p. 1416).
Yet, building market knowledge triggers a second dilemma, that is, the paradox of information availability (Welch et al., 2016). One might consider, as a logical third assumption of the U-model, that the ease of access to data, plus the wealth of information and the abundance of digital channeled sources, has a great potential of market knowledgeability. However, the sorting of specialized and quality data entails added challenges as to the absorptive capacity of the firm to acquire external knowledge that exists elsewhere and learn indeed through the identification, assimilation, and exploitation of that same information (Cohen & Levinthal, 1990; Filippetti et al., 2017; Lane et al., 2006; Zahra & George, 2002). Some scholars claim that the extent of knowledge acquisition is determined by the prior awareness of the significance of the information, prior knowledge, and international experience (Ardichvili et al., 2003; Cohen & Levinthal, 1990; Dyer & Hatch, 2006; Eriksson et al., 1997; Gulati & Gargiulo, 1999; Hohenthal et al., 2003; Welch et al., 2016).
Beyond these internal paradoxes hovering over the firm, the U-model in the 1970s had, furthermore, to accommodate the business environment’s dynamics of change observed in the subsequent decades, with a chaotic and, to some extent, unpredictable nature. Additional VUCA in the business ecosystems worldwide, disturbed the interface’s equilibrium between organizational strategies and their competing environment (strategic drift), and subsequently, oriented the organizations toward corrective paths for strategic fitness, consisting of the improvement of their strategic agility toward the business environment (Choi & Ruona, 2011; Johnson et al., 2008; More et al., 2015; Sammut-Bonnici, 2015; Weber & Tarba, 2014).
Several scholars raised questions in the last decades of the 20th century as to the contemporaneity of the U-model (Weerawardena et al., 2007). A growing criticism surrounding predominantly the establishment chain and psychic closeness was anchored on evidence of accelerated internationalization and leapfrogged establishments, emphasizing the virtues of alternative perspectives, such as network affiliations; entrepreneurial approaches toward opportunity-seeking; capabilization and competitive advantages’ formation; and global competition and disruptive technological development (Coviello, 2006; Dunning, 2001; Griffith & Harvey, 2001; Oviatt & McDougall, 1999; Prange & Verdier, 2011; Sarasvathy, 2001; Zahra et al., 2000). Forsgren (2016) has recently explicitly stated that a specific model [the 1977 model] is not needed, because firms’ internationalization is fully captured in models of firms’ general business behaviour, for instance in models of how firms’ grow by strengthening their position in business networks. (p. 1142)
The discrepancies of the original rationale of the 1977 model to the contemporary business practices was accentuated by newer frameworks adding alternatives to the pallet of architectures of IB, but with less-contingent designs portrayed in the rational, sinusoidal, and nonlinear patterns of foreign venturing (Lukason & Vissak, 2016; Prange & Verdier, 2011; Sheppard & McNaughton, 2012). For instance, early internationalization, or born-global (BG) establishment, is advocated as more suitable models for current times, due to the detachment to gradualism and bold risk-taking (Ciravegna et al., 2019; Dimitratos et al., 2008; Gabrielsson et al., 2006; Luostarinen & Gabrielsson, 2006; Schwens et al., 2018).
Yet, one question may naturally be formulated. How do early internationalizers, often possessing fewer resources may operationalize such model? This leads to the fourth assumption of the U-model, in which firms compete as solo-players in foreign markets selected by their separate country-specificities. This contrasts with the assertions of other scholars of a networking-playing mode for a higher fruition (Coviello, 2006; Dyer & Hatch, 2006; Forsgren, 2016; Guercini & Runfola, 2010; Gulati & Gargiulo, 1999; Håkansson & Ford, 2002). Moreover, the benefits of business networks had been acknowledged in Central Asia over a century ago, with the development of structures as the guanxi, keiretsu, or zaibatsu still adopted by large corporations (e.g., Asamo, Fujita, Furakawa, Mitsui, Mitsubishi, New Oriental, Northern Light Venture Capital, Sina Corporation, Sumitomo, Okura, Yasuda, and Youku Tudou Inc.) to whom their virtues are inherent to the principle of cooperation (i.e., co-development; management exchange mechanisms, and information; participation in senior management committees; partial cross-shareholding; and interlocking board memberships) and principle of solidarity (i.e., reciprocal monitoring, lending, or stable financing), which in turn, insulated firms from market pressures and reduced at a firm level of the transactional risks (Brouthers et al., 2014; Collinson, 2015). This self-protective role of the members for the attenuation of weaknesses mostly small and early-stage organizations (liability of newness and smallness) against underlying risks and lack of external legitimacy differs substantially from the Western world (Xin & Pearce, 1996); however adhering to the occidentalized notion of networks as dynamic entities comprising issues of social exchange, embeddedness, position, power, roles, ties, strength, and reciprocity (Cross & Prusak, 2002; Leppäaho et al., 2018).
However, business network theory is likewise contested by agency and gatekeeping theory, since its access to information may contain risks as to the involuntary loss or withholding of data, and/or the deceleration of internationalization (Guercini & Runfola, 2010). Yet, Johanson and Kalinic (2016) posit that the deceleration is not a network exclusive phenomenon. Their research on international commitment, focusing on the coordination and synchronization of co-existing international value chains at different locations, also raised issues with regard to the circulation of information across subsidiaries and the integration of knowledge. The authors claim that the reciprocal influence and interdependences of the marketplaces, also mediates the speed of internationalization, and the tendency to accelerate and/or decelerate the pace of the operations. Moreover, they corroborate with agency/gatekeeper’s theory on the connection between deceleration and information availability paradox, reiterating that the root of the problem lies on three aspects of the modus operandi of information gathering: (a) the acquisition of knowledge, (b) integration of knowledge, and (c) the coordination and allocation of resources (M. Johanson and Kalinic, 2016, p. 839).
In addition, insights from the New Internalization Theory (NIT) with regard to the internal (or external) aspects of the international strategic governance highlight the importance of the individual-level aspects that determine the internationalization behavior, asserting that the notions of bounded rationality and bounded reliability regarding the intended dimension of both are undermined by individual limitations. Thus, the focus of internationalization management ought to be the creation of organizational contexts where the risks of managerial discretion as to the centralized decision-making is mitigated for the sake of further addition and appropriation of value (Coviello et al., 2017). These authors, pinpoint the latter as a downside of the Uppsala rationale, as the overlooking of individual managerial behavior, and its associated constraints and risks. Moreover, these authors claim that the case-model also ignores external macro-level influences environment, as the impact of technological disruption in IB theory, and therefore suggest an alternative model, the three-layer model accounting: (a) the macro environment influences, (b) the governance of multilateral exchange comprising the Uppsala’s state and change variable, and (c) the micro level influences.
Conversely, Lukason and Vissak (2016) on their research upon the rare earth metal (REM) producers’ internationalization, focuses their attention on the bottom line question of international failure and international success (IS), through the observation of the crossbred of the markets with the financial performance, as the latter is considered a key measurement of IS, which is defined as the ability to effectively recombine firm-specific advantages (FSAs) across borders (Coviello et al., 2017). Here, Lukason and Vissak (2016) argue that pace (fast or slow internationalization) per se, does not determine performance, referring to the connection of financial performance and international activities. In fact, the authors advocate that the widespread internationalization failures are due to the firm’s adoption of conventional models as a process or BG approach. Lukason and Vissak (2016) posit a serial nonlinearity (SNL) model of a rather unpredictable and selective commitment within a portfolio of already established and prospective markets, which implies a fluctuating approach, envisioning market-entry and commitment and divestment and re-entering adapted the dynamism and conditions of the markets.
Although, Håkanson and Kappen (2017) advocate a less hectic approach. Their model (the Casino model of internationalization) argues a deliberately strategy combining periods of stabilization with periods of market development, with establishment resembling a wave-like pattern. Considering a test with a PD ranking of 20 countries according to four types of commitment (agent; sales subsidiary; manufacturing subsidiary; sales and manufacturing subsidiary), they assert an “alternative and complementary model of the internationalization process of the firm,” representing an alteration to the “Uppsala School as a paradigm” with an allegedly better fit to respond to the “conditions of environmental uncertainty and partial ignorance” (Håkanson and Kappen, 2017, p. 1103–1104).
Such an immense theoretical upsurge in the last decades, the next sections immerse into both, empirical counterevidence of Uppsala as a disposable model, and the evolving path of this school of thought by tracking relevant researches conducted by the University of Uppsala itself and their partnering institutions/researchers and also by their following researchers. This dynamic here dubbed as the “Uppsalian reasoning,” that is, the own applied research of the first ones and the related research conducted by third parties is unified in the publishing into the conceptualization of further descending models deriving from the 1977 model. This article compares an evolutionary trend until their latest advocacy with other frameworks to answer to the aims of the investigation and determine whether the Uppsala is an enduring and, most essential, a germane model to the current times.
Counter-Evidence of Uppsala’s Superannuation
Two of the most extraordinary and overshadowed aspects pointed out to the U-model since its foundation is the unusual capacity to accommodate large-scale data observations, and its flexible design which allows an evolutionary-thinking of constant reconfiguring of its ontology and rationale (Håkansson & Kappen, 2017). For instance, the Uppsala reasoning as the raison d’être of the original model, which Håkansson and Kappen (2017) refer to as the “Uppsala paradigm” it demonstrates a tendency to adapt itself to conditions and dynamism of the business ecosystems (Forsgren, 2016). This latter claim is furthermore corroborated by its “architects” who self-proclaimed that: the two frameworks [the mechanism of internationalization; and, eclectic (Oli) paradigm] in their present shape are inconsistent . . . We believe our model [the general model of the evolution of the multinational business enterprise (MBE)] accommodates, not new methodologies but a different theoretical approach . . . (Vahlne & Johanson, 2017, p. 189 & 203)
This evolutionary path is perhaps the upholding motif for the fascination of many academics surrounding the “Uppsala stage model—including psychic distance concept” as the model still rates as the second most reviewed framework within family-business (FB) internationalization context, according to Pukall and Calabrò’s (2014, p. 108) research focused on 72 articles from 1980 to 2012. In addition, the empirical researches of Caputo et al. (2016), Abrantes (2018) and Nordman and Tolstoy (2014) corroborate that the concept of PD, one of the cornerstones of the model, is still a sound phenomenon related to SMEs’ internationalization.
Caputo et al.’s (2016) research on 24 firms in Central/Eastern European countries (Poland and Czech Republic) revealed that their internationalization is highly influenced by physical, cultural, and language proximity features of the destiny-markets. Likewise, Abrantes (2018) observed that regardless of the seniority in foreign markets, the Portuguese SMEs of the steel industry seem to favor foreign markets of language proximity, prioritizing the market-entry into the Community of Portuguese Language Countries.
According to these evidence, PD is a phenomenon still very much alive in the heads of practitioners across industries; therefore, pertinent is the research of Nordman and Tolstoy (2014) on 314 Swedish SMEs verifying that some of the Swedish firms, with higher sensitivity to uncertainty and risk-taking (which lead to psychic distancing), were actually the ones who had undertaken larger efforts to reinforce the mechanisms related to the analysis of information, and to the enhancement of market-knowledge capabilities. In this sense, the study observed an evolution of the strategic thinking, from the avoidance of PD markets to the usage of high PD market’s barriers and dissimilarities in their favor to attain further organizational learning and adaptation, at country and regional-level.
Under harsh environmental conditions, in which firms opted in the past to simply avoid risks, these evidence above suggested a behavioral shift of some firms toward a counterintuitive direction, based on the learning, adaptation to those more PD markets, focused specially on the sharpening of customer relations. Thus, past risk/avoiders evolved to risks/uncertainty controllers, with higher ratios of market learning, resilience, and performance abroad. Corroborating these authors’ findings, the survey of Vahlne et al. (2017) on managerial risk perception applied to 309 chief executive officers (CEOs) and chief financial officers (CFOs) in the Nordic countries, revealed that the management under uncertainty markets overseas stimulates the exploitation of opportunities, which in turn, reduces the level of uncertainty, and keeps risk-taking at low-levels. Thus, uncertainty it may be perceived as a positive phenomenon of risk reduction. Conversely, Forsgren and Hagström (2007) observation of eight internet-related firms revealed a low dependence on short PD, as firms adopting contrarily, fast and discontinuous explicit internationalization strategies in their choice of markets of entry, focusing rather in one aspect (i.e., the potential size of the sector). Therefore, their internationalization strategies were spuriously related to PD, but exhibiting a positive correlation to Smithian factors of scalability and effective market dimension, comprised in the theory of absolute advantage (Schumacher, 2012).
In addition, prior research from O’Grady and Lane’s (1996) demonstrated that geographical, cultural, and linguistic proximity is not synonym of safeness and financial success. The internationalization of Canadian firms of the retail sector to the United States, showed that from a universe of 32 firms, only seven (22%) of them managed to succeed. This brings together an example of the PD paradox, since culture similarities which apparently make it easier to enter a host-market, though may comprise fewer and subtler differences that may hamper the firm’s performance, including business practices, that requires a prior stage of preparedness beforehand initiating an internationalization attempt. Thus, a lesson to be taken from O’Grady and Lane’s (1996) research is the avoidable sense of complacency associated with psych closeness (Magnusson et al., 2014).
In turn, the success of international ventures is still imprisoned by the managerial discretion, thinking and decision-making on PD, and absorptive capacity and their paradoxes (Costa et al., 2016). These authors argue that, if on one hand, business network interactions are a source of knowledge and learning, and subsequently, business collaborative networks are an alternative path to the U-model which facilitates the internationalization of SMEs (as important channels of information and knowledge; influencing the upper echelon; influencing decisions on foreign market selection and entry mode; accelerating international commitment and overcoming resources constraints); however, the excess of availability of information also hinders SMEs which over face many obstacles regarding the filtering of the correct information and managing it effectively. Bhatti et al. (2016) refer to it as the “knowledge gaps” of the firm, which are decisively fulfilled only when a knowledge strategy exists for capturing it and disseminating across the organization. This leads to effective market intelligence, firm’s process innovation, and higher profits. Therefore, this is consistent with Forsgren’s (2016) claim that an unweighted decision of the firm to adopt a networking-playing mode of competition can entail severe damages, namely augment the effect of the liability of outsidership (concept which is described in the following section).
The U-Model’s Evolutionary Path
First paradigmatic shift (from process internationalization to business network view)
A significant step given toward the reform of the neoclassic paradigm, was the abandonment of the tacit notion of international competition as a solo endeavor of the firm (Johanson & Vahlne, 2006; Welch et al., 2016). The assumption that firms as standalone competitors was replaced by a logic of intertwined competition. Networks, as webs of relations, encompassed the willingness to maintain, develop and strengthen institutional trust, and spark social and intellectual capital stocks with other network members. Social capital referred to the exchange process within the business relationships constituting the foundation for trust, cooperation, and collective action whereas intellectual capital ought to arise from the new knowledge derived from social capital stocks.
In this business network view (BNV), relationship was defined as a cumulative process, continually established, maintained, and developed to provide short-term return, create network positioning and ensure the long-term survival of the firm (J. Johanson et al., 1988). The commitment of the firm to engage in such business networking processes assumed itself as a determinant role in reducing uncertainty, acquiring new knowledge (and/or accelerating it), enhancing the control over the environment, and tryout an entrepreneurial discovery of the hitherto unknown, as market opportunities for exploration (Johanson & Vahlne, 2006; Kirzner, 1973; March, 1991). This perspective has driven the U-model toward the fashion of the business network internationalization process (BNIP) model, which underpinned the firms establishing positions in relation to counterparts in foreign markets (Johanson & Vahlne, 2009).
The commonalities between BNIP and the original U-model laid first on the retaining of the 1977 model design despite incorporating features related to the architecture and market structuring of business networks. Although, other features were observed with regard to risk and knowledge sensitivity, that is, the distancing from the original model as to the risk-taking behavior and the reinforcing of market-knowledge requisites by extending the breadth of other types of knowledge (network, sociocultural, and experiential) (Wach et al., 2018).
The BNIP diverged though from Coviello’s (2006) approach toward the network-development of early-stage internationalizers, international new ventures (INVs), and BG firms. The two approaches are here argued as complementary ones, for their consistency to Mejri and Umemoto’s (2010) model on roles of knowledge in the internationalization process. Johanson and Vahlne (2009) model (BNIP), is oriented toward experiential knowledge-acquisition (comprised of network knowledge, entrepreneurial knowledge, and sociocultural knowledge) in a phenomenon perceived mostly as belonging to mature internationalizers, while Coviello (2006) is focused rather on market-knowledge acquisition typical of early internationalizers (Wach et al., 2018).
According to this business network view (BNV), market actors engage in interdependent relationships through social exchange processes, leading to knowledge gains, indirect learning, trust-building, and strengthening of the network positions (Johanson & Vahlne, 2009; Wach et al., 2018). These authors advocate a critical correlation between liability of outsidership and liability of foreignness, as the acquisition of experiential knowledge, is argued to be a prerogative to lock the harmful extent of the latter (liability of foreignness). Moreover, they posit that the internationalization process is a mode (i.e., the mechanism) of developing relations (i.e., the goal) (Johanson & Vahlne, 2003), reversing the internationalization primary objective to the development of borderless relations, and relegating the internationalization, as the entry and establishment, to a secondary role, as a by-product of the prior. Furthermore, international networking links to an entrepreneurial orientation (EO) to the seizing business opportunities (Schweizer et al., 2010).
Second paradigmatic shift (from internationalization process to international capabilization)
Welch et al.’s (2016) argued a paradigmatic shift from the neoclassical to the behavioral paradigm in the Uppsala’s internationalization, comprised of the elimination of assumptions from neoclassic economics and the building of new assumptions grounded upon behavioral theory. Thus, with the uplifted importance of relational and experiential knowledge for the improvement of network positioning, the notion of “process” lost vigor, to become merely an attribute embedded in the new paradigm. Yet, some scholars argue that the processes related to knowledge are influential in international context. Eriksson et al. (1997) associate the knowledge management process, as to the combination of two different knowledge bundles (business knowledge and knowledge about internationalization) arguing to be determinant for the international performance, while Wach et al. (2018, p. 1) in a study conducted upon 355 Polish firms assert EO, which defined as an entrepreneurial process within foreign markets is intrinsically related to knowledge utilization and both are a determinant of the success of internationalization process.
Although, the BNIP emphasized in their state variables “knowledge opportunities” which according to Gabrielsson et al. (2010) is reductive of the international entrepreneurial orientation (IEO) which shall incorporate, according to Oviatt and McDougall’s (2005) the anchors of international entrepreneurship (IE), as the triad of innovation; proactiveness, and risk-seeking behavior (Wach et al., 2018). Schweizer et al. (2010) confronted then the BNIP with empirical data suggesting an alternative archetype, the entrepreneurial model of the internationalization process (EMIP).
Despite the structural similarities with the business network model (Figure 1), as the envision the environment as dynamic, nonlinear where its actors are laced within networks, with state/change variables interconnected and mutually affected by the other, the main conceptual difference of the EMIP is a broader outlook of international entrepreneurial action.
The model functions as a hat covering different subtopics (by-products; efficiency and expansion; opportunity identification, development and exploitation; dynamic capabilities (DC); Knightian uncertainty; risk-taking and affordable loss; networks; and business relationships, trust, and commitment) and within the Uppsala paradigm, is the first to argue explicitly the development of capabilities (i.e., entrepreneurial capabilities) for the formation of firm-specific advantages (FSA), flagging a link with the resource based theorists.

Uppsala model—Paradigmatic shifts.
The EMIP model gives ample attention to opportunity-seizing, based on a sense of entrepreneurial alertness, as a capability for recognizing the value of new information and idea-generation, and believe that solo entrepreneurs are not so effective in identifying opportunities as network-entrepreneurs with wider access to extended information obtained throughout relationships’ social exchange processes (Ardichvili et al., 2003; Koller, 1988).
As an entrepreneurial behavior model, the internationalization is conceived as a by-product of network positioning. The authors are aligned with Sarasvathy’s (2001) effectuation process, in which effectual entrepreneurs are not tied to pre-conceived market universe and tend to search for new customers within their immediate vicinity, geographical or social network, while following two main principles: the affordable loss principle, and the strategic partnerships principle, which share basic similarities with the BNIP. However, both the effectuation process, and the EMIP are partnership-builders rather than focus on risk-avoidance and therefore focus on knowledge build from the systematic competitive analysis of market attributes (i.e., a causal reasoning) which is less entrepreneurial as what the strategic thinking is concerned. Hence, the BNIP is supportive of a shift from the reflexive causation process to a dynamic effectuation process through the action and interaction with others, in which firms deal a priori with environmental contingencies, instead of reacting to the dyad cause-effect circumstances.
However, the EMIP is on the fringe between two overlapping cross-border business processes: the internationalization process and the globalization process, where internationalization precedes the globalization (Gabrielsson et al., 2006). The first (internationalization process) explains the transition from a national to international and the latter (globalization process) the transition from international to global (Vahlne et al., 2011). The distinction between both lies in its morphology. Internationalization is bi-dimensional (geography and the mode of operation) and globalization is four-dimensional (geography, mode of operation, configuration, and coordination). The configurations refer to the design of the value chain while the coordination is the system of adjustment of roles and functions of the interdependent units of the group.
The Uppsala globalization process model (UGPM) argues though a distinctive role of HQ and subsidiaries, and even within the latter, differing across the organization, regionally and group-wide to satisfy specific local demands and ensure efficiency and effectiveness at a global level and the global objectives’ accomplishment. State variables were modified in the model to ensure the units’ coordination, adding also the reconfiguration of the value chain and redesign of coordination mechanisms. Thus, the UGPM contributed to the reinforcement of a shift in mind-set from a focus on the external environment (marketplaces) into the firm. Moreover, if the previous model (EMIP) flags the importance of capabilization, here the locus of attention has strengthened the prior within the internal environment (the firm), enlarging the spectrum of DCs, which in the prior were merely circumscribed to cognitive DCs. In this model, attention is given to managerial capabilities, accentuating this inflection toward the grasp and preparation of the firm to compete internationally.
The rationale of DC extension in the prior, is continued by the General Multinational Business Enterprise evolution model (GMBEE) which enlarged their assertions toward the broad capabilization of the firm (Vahlne & Johanson, 2013, 2017); This archetype extended the spectrum of the multinational enterprise (MNE) conception, accommodating a larger number of capability requirements related to internationalization, and a far more holistic vision upon internationalization-related processes, decisions, and positions, in what the authors called it a multinational business enterprise (MBE). On the MBE’s mechanism, internationalization combines elements of the Penrosian evolutionary theory of the firm, entrepreneurship theory, DC theory, and theory of management of uncertainty. Thus, the foundations of the U-model upon risk and knowledge and their underlying paradoxes are still present, however, profoundly aligned with the dynamic capabilities view (DVC) observable in the vast number of DCs incorporated in the model: entrepreneurial capability (Arthurs & Busenitz, 2006; Teece, 2016; Weerawardena et al., 2007), networking capability, marketing capability (Weerawardena et al., 2007), adaptive capability (Wang & Ahmed, 2007), R&D capability (Rothaermel & Hess, 2007), and absorptive capacity (Wang & Ahmed, 2007; Zahra & George, 2002).
The Casino model breaks with some of the assertions from previous researches within the Uppsala paradigm (Håkanson & Kappen, 2017). The authors question the misfit of an incremental logic with the empirical results, and posit that firms deliberately implement strategies combining periods of stabilization with periods of market development, as a wave-like pattern with a sinusoidal function. Moreover, the model builds on the assumption of difficult accurate predictions of foreign markets, under scenarios of downside outcomes, uncertainty, and partial ignorance, lead the firms to arguably follow rationale strategies of international diversification for limiting the potential impact of losses, by simultaneous establishing a number of agencies and/or subsidiaries in different locations while pursuing foreign market opportunities.
The apparent risk-seeking behavior, is based on a contrary motivation, the willingness to reduce the dependence to a certain market and the possible failure, by following a “casino internationalization” analogy of gambling in a roulette table where placing more bets increases the probability of winning.
Moreover, the model argues the realization of the potential for attaining economies of growth by an optimal utilization of available capabilities. Thus, the deploying and exploitation ought to ensure non-location bound capabilities which in turn require further capabilities for the structural adjustment, and administration of these changes across the existing resources and systems within the organizational sphere. Hence, the deployment of capabilities is dependent upon internationalization decisions which in turn are constrained by PD (Evans et al., 2000).
In this context, Safari and Chetty (2019) expanded the notion of PD through a multilevel framework applicable to pre- and post-entry internationalization. This multilevel psychic distance (MPD) model cascaded PD into five subsets of attributes (country factors, business factors; founders and firm’s PD; PD between firm and a bridge-maker; and use of trust and knowledge on PD). Their study demonstrated that a great extent of difficulties in the post-internationalization were not related merely to country and business factors but to its own limitations (firm’s PD) as to the country and business factors. In this sense, for the attaining higher economies of growth through the deployment of optimal capabilities, this limitation of the firm’s PD requires ancillary knowledge and trust from/to the markets. Here, the reciprocal firm and bridge-maker relation is critical for determining international success or failure. The study highlighted though that the market selection seems to be based on the country factors, however undermined the individual managerial bias with regard to exporting decisions, since it was observed no evidence of PD influence on managerial exporting decisions.
Method and Research Framework
According to MacInnis (2011), conceptual contributions that can guide academic research forward, are intrinsically pillared in four typologies (envisioning, relating, explication, and debating) that reflect a conceptual thinking route of either a process of discovery or a process of justification. Here, the coverage of this topic (i.e., endurance of neoclassic internationalization theory, testable on the light of the Uppsala School’s case) implies the usage of the full spectrum of discovery and justification processes, since it includes the usage of a range of information-processing activities, such as the identifying and revising the observable characteristics of each of the testable models, draw a relational explanation between the original 1977 model and the remaining models, and debating upon its evolution.
In this sense, an integrative review is here applied due to its methodological adequacy to review theories and analyze methodological issues of a particular topic (Whittemore & Knafl, 2005). An integrative review it may be described as a “the most comprehensive methodological approach to reviews, and it allows including of experimental and non-experimental studies to fully understand the phenomenon analyzed” (Souza et al., 2010, p. 103). Therefore, allowing the combination of theoretical and empirical literature, the method has the virtue of contributing both to theory development and applicability to practice and policy-making.
This method is based on Cochrane’s evidence-based practice (EBP) and follows a PICOT logic of problem identification; intervention of interest; and comparison, outcome presentation, and timeframe contextualization (Whitehead, 2013). The application of this method implied the adoption of a research framework comprised of six stages, starting on the preparation of the guiding questions (exhibited in “Introduction” section), and following a sequence of searching of literature, gathering of sampled data sources, critical analysis, data evaluation and discussion of results, and presentation of the review.
The critical analysis process implied a reduction and comparison of data. In the first (reduction) literature was classified according to a chronological order and divided into two subgroups (Whittemore & Knafl, 2005). The first subgroup of manuscripts originated from the Uppsala University and their partner institutions, and a second subgroup of other researchers were either followers or opponents. Then, the main substance of the articles (categorization and summarized description) was extracted that obeyed to an ordering and coding of features. Furthermore, the previously analyzed literature in a separate manner, required at the moment of data comparison, the identification of associations and detection of patterns, for further presentation of data displays, as suggested by the content/qualitative data analysis (QDA) methodologists Miles and Huberman (1984). The output of this data analyzes stage, that is, the data display, is displayed in a matrix, presented in the next section.
Results and Discussion
Considering Whittemore and Knafl’s (2005, p. 550) systematic analytic method applicable to integrative reviews, the table below exhibits the U-model compared with six descending models of the Uppsala School given rather attention to recent publications within the two decades due to its theoretical richness and contemporaneity. The purposive sampling accounted also disparate years and research focus within IB theory (i.e., networking, IE, dynamic capabilization, and rational incrementalism). The authors structure these focal articles which account four scholars from the Uppsala University (Aswo Safari, Jan Johnson, Philip Kappen, and Sylvie Chetty) and associate researchers (Inge Ivarsson, Jan-Erik Vahlne, Lars Håkanson, and Robert Schweizer) in total representing the partner institutions (Copenhagen Business School, Mälardalen University, University of Eastern Finland, and University of Gothenburg). Nevertheless, the drawing of conclusions (in “Conclusion” section) as to the aims (Aims 1 and 2) of this investigation revealed in “Introduction” section, accounts besides the cross-checking of literature from third parties (followers or non, critics and antagonists), which suggested the advancement of internationalization theory, regardless of the Uppsala’s assertions about its adaptation to the VUCA environmental circumstances.
The results from the integrative review process, comprising the “searching and sampling of literature,” “data collection,” “literature review stage,” “critical analysis of the studies,” and “data evaluation stage” are below presented in this table (Whittemore & Knafl, 2005, p. 548; Souza et al., 2010, p. 102).
Looking at Table 1, it is observed that from its establishment until the last iteration in 2019, the Uppsala rationale has evolved substantially in its fundamental characteristics. The scope of theoretical circumscription was augmented; with some features losing notoriety or being discarded, while others traveled 42 years until the Safari and Chetty’s (2019) multilevel PD model.
Paradigm Evolutionary Process—Uppsala School.
Source. Håkanson and Kappen (2017); Safari and Chetty (2019); Vahlne et al. (2011); Vahlne et al. (2017).
Note. UM = Uppsala model; BNIP = business network internationalization process model; EMIP = entrepreneurship model of internationalization process; UGPM = Uppsala global process model; CM = Casino model; GMBEE = general multinational business enterprise evolution model; INV = international new venturing; BGs = born-global firms; MPD = multilevel psychic distance.
A feature of Model x reinforces the equivalent one in the previous Model y.
Model x devalues the feature of Model y.
A feature of Model-x replaces another from the previous Model y.
Throughout the time, the backbone features of the 1977 model, that is, a process-nature and the reliance on market knowledge as a core capability (UM1 and UM4) signaled the utmost capacity to resist. In addition, the augmentation of the theoretical scope and the capabilization breadth is noticed in the excerpt of articles along the chronological line, in an upward spiral of problematics/phenomena raised, and on the number of capabilities required to respond to it.
Looking at Table 1 and comparing the columns “main characteristics,” “continuity chain,” and “rupture” it is discernable the separate contribution of each article (column “main characteristics”), and its evolution by cross-referring to the continuity chain, which registers the reinforcements made from one model to the next, or to the themes that were omitted, devalued, or contradicted, by its replacement by another feature in the subsequent model.
For instance, the focus on country-specificities (UM2) regardless of its overseas interactions or exposure was abandoned to emphasize cross-border relations developed within multiple agents. Consequently, this demanded the extension of capabilities, to cover relationship and trust-building capabilities (BNIP4); entrepreneurial capabilities (EMIP3); opportunity sensing and recognition (CM4); managerial capabilities related to subsidiary/partnerships coordination capabilities (UGM3; MPD3), or internal learning, absorption of information, and knowledge development (UM4; EMIP3; CM4; GMBEE4).
In order to comprehend though the adaptation process of the U-model in parallel with its evolution, the features of case-model were it is cross-checked its continuity chain with the features of others models presented in the “Obstacles, antagonism and theoretical advancement” section (Table 2).
Uppsala’s Adaptation to New Theoretical Frameworks.
Source. Own elaboration.
Note. BNIP = business network internationalization process; MPD = multilevel psychic distance; BAG = born-again global; UGPM = Uppsala global process model; NIT = new internalization theory; SNL = serial nonlinearity; GMBEE = general multinational business enterprise evolution model.
The solo-playing mode of competition and envisioning of internationalization as being dependent on the country-specificities of host-markets were abandoned in the BNIP. Nevertheless, in the latter model it overlooks conceptions, such as liability of newness and smallness, knowledge accessing alliances as looser forms of cooperation, and the potential of reversion of the traditional outside-in logic for mitigating the liability of outsidership through an inside-out exploitation of insiders to explore with new-entrants (Yamin & Kurt, 2018; Álvarez et al., 2016; Xin & Pearce, 1996).
Furthermore, the BNIP model advocates the importance of capabilities related with relationship and trust-building development, which is enhanced in the MPD model with the uplifting of the idea of trustworthy relations with middlemen, as gatekeepers of business exchange and therefore the bridge-makers whom may regulate the success/failure at both a pre-entry and post-entry phase of internationalization.
As to the notion of BG early-stage positioning, an epistemological wall it seems to separate though the scholars proclaiming this fast-internationalization mode, against the UGPM, since the globalization process is not connoted in the latter framework with an increment in the pace or speed of internationalization, but it refers to an iteration of market-entries leveraged by the development of international borderless relations. However, in the side of BG theorists, the failure to achieve a status of “pure born-global,” that is, as becoming a successful performer it leads to a BAG re-entering which then it approximates itself with the UGPM rationale as it follows a process or reestablishment chain.
The cascading of the PD in Safari and Chetty’s (2019) MPD model into five different categories extended the coverage of Uppsala rationale to the individual aspects in internationalization behavior, as the importance of the founder/manager and the bridge-maker, it reinforces the prior arguing of the of individual managerial capabilization (the UGPM) within multinational companies (MNCs) context. The fluctuating approach argued by the SNL is counterpointed by Håkanson and Kappen’s (2017) Casino model asserting a rather sinusoidal approach based on wave-like patterns of incremental investment. Concomitantly, the GMBEE model defends a broad capabilization of the firm for the adjustment toward environment circumstances with benefit of the firm’s performance. Still, both approaches remain at this point, irreconcilable. Yet, Coviello et al. (2017, p. 1153) argue that the Uppsala’s GMBEE model is not responsive to a particular macro-environmental feature, that is, the businesses’ digitalization with subsequent enhancing of platform-based competition with inherent impact on IB, as these authors claim that this is a disruptive phenomenon capable of altering the internationalization process in several of aspects as, timing; pace; rhythm; location; entry-mode choices; foreign markets learning; knowledge recombination; accessibility/pre-emption to resources and capabilities; and the ability of the firms to overcome the liability of foreignness.
Conclusion
The answer to the research question, how does the U-model endure? Lays on a dual evolving path of: (a) theoretical evolution and (b) constant adaptation toward environment conditions.
At the beginning of this article, the myth of superannuation of neoclassic theory is introduced on the light of contemporary VUCA challenges of the business ecosystem and latter literature. In this context, this research instrumentalized the prominent internationalization model (Uppsala) established in 1977, to comprehend if over 40 years of societal transformations the model it grew into a static, old-fashioned and/or inadequate condition. Conversely, the case-model revealed a dynamic of rejuvenation, delivering significant contributions to the advancement of the knowledge in the field, as it is for instance manifested in the last three publications of Håkanson and Kappen (2017), Vahlne and Johnson (2017) and Safari and Chetty (2019) pushing the conceptual boundaries toward the breaking down of PD; or fashioning a wave-like internationalization pattern; or introducing tangent conceptualizations, such as the bridge-maker, history dependence, or process ontology; furthermore supported by empirical evidence corroborating these paradigms.
As to the aims disclosed in the “Introduction” section, it is perceived as a positive enduring over time (Aim 1) and utility (Aim 2) of the model. Although, these conclusions ought not be extrapolated and conjectured to other frameworks, thus the results are merely applicable to this model, since the enduring of other business international-related theoretical perspectives are not under observation. This research asserts that the case-model evolved categorically in its conceptual logic altering its conceptual-thinking system in terms of broadness and updateness, targeting environmental mutations and the novelties introduced by others scholars. Such attainment is fueled by the continuous dynamics of: (a) the investigation projects of the academic community beyond the Uppsala’s thresholds and (b) due to the evolution of the societies and business ecosystems worldwide. Thus, a dual reciprocity of influence is noticed between researchers from Uppsala and from different quadrants; and moreover, between researchers and the external environment context. It is argued that the Uppsala School was geared by a reactive adaptation sense and by the craving of extending the state-of-the-art. The self-consciousness of the Uppsala researchers as to deliberate evolution of societies and its challenges for firm’s adaptation and is perceived in the following statement (Vahlne & Johanson, 2017): The key features of the modern firm: process rather than structures orientation; network rather than stand-alone unit; business exchange rather than production; pro-active and entrepreneurial rather than passive; heterarchical (decentralized) rather than hierarchical. (p. 1088)
Certainly, this supports the assertion of a stretching of the phenomena covered by the Uppsala School and the adaptation of their reasoning to current times. Second, it conveys a conceptual enrichment and progress in terms of market suitability, accumulating features of several descending models, and ensuring a more up-to-date viewpoint. Third, it allows a debate about the current morphology of the Uppsala paradigm, due to the multiple modifications of its rationale. For instance, what are the backbone ideas that describe the current theoretical position/s of the Uppsala Paradigm? What does the Uppsala stand for nowadays regarding the internationalization of the firm? The discussion here raised is aligned with Welch et al.’s (2016) assertion that the U-model has embarked in an “intellectual journey,” attending a paradigmatic shift as to the evolvement of the neoclassic assumptions to meet new paradigms upon by surrounding itself of new behavioral assumptions.
It is argued an increasing multifocality of the Uppsala thinking and a converging assertiveness toward environment mutations. This research will not be drilling down the answers to those questions, since, the bottom line question here to be answered is, how does the U-model endures? Pillared on renewed research with constant foci on environment changes, the Uppsala paradigm it has positively adapted and endured over time (Aim 1), as demonstrated in the “Results and discussion” section and corroborated by empirical studies on “The U-model’s evolutionary path” section.
As to the enduring of utility (Aim 2), Table 1 (Paradigm evolutionary process—Uppsala School) in the “Results and discussion” section, attests an evolution of rationale demonstrated in “Contribution” by the cross-observation of “continuity” and “rupture” which together illustrate the enduring features and the abandoned features, therefore, drawing the evolutionary line. Moreover, the quest for enduring utility (Aim 2) implied furthermore not solely “evolution” but “adequacy” of reasoning to the environmental challenges. Such strategic fitness, is proven in the “Counter-evidence of superannuation” section in which the disclosed internationalization-related studies support the results that are obtained here, and therefore, corroborating our claim of a positive fitness of the model.
In parallel, a striking feature the evolution of the Uppsala’s paradigm is a clear approach toward the capabilization frameworks. The model incorporated with time newer organizational capacities (OCs), and subsequent increase of its number. This assertion is corroborated for instance by Wach et al. (2018). This capability-building logic allowed the extrapolations of two additional ideas. First, capabilities were foreseen as facilitators of competitive equalization definable as a responsive process of approximation to market requirements, for reducing or neutralizing the effects of uncertainty and risks and/or shortening the liability of outsidership as to the market and its stakeholders. Second, the Uppsala School, is argued here, not merely as an internationalization process model, but as an international capabilization model (ICM), since the added-capabilities are consistent with the DCV within the resource-based theory which argues the importance of the possession of first-order or DCs as critical for sustaining competitive advantages (SCAs).
As noted in the previous paragraph, may be deduced that the contribution and singularity of this article lays upon two major ideas of relevance for both the academia and practitioners, especially for MNCs, that is, the demystification of the epithet of superannuated model, and the urge for the theoretical development of ICMs for the advancing of IB field, and subsequent increase of performance and wealth of MNCs. Thus, ICM it assumes itself as an emerging field to evolve in parallel with the theories of internationalization, globalization, IE, corporate governance, IB, international networking, and adjacent to other interdisciplinary fields.
Research Limitations
From the nature and objectives of this research, the main limitation referred to the circumscription of the project to the spectrum of a literary revision. Hereupon, it could be inferred that the methodological option for an integrative review could be thoroughly broadened by the natural extension of the research paradigm into an empirical one, allowing thus the enlarging of the methodology, for instance, to a content analysis (CA) one.
Furthermore, it is indisputable the richness and depth of qualitative research, inherent to CA frameworks, QDA’ protocols, data coding, data crunching, and diagrammatic representation of data associations (Gioia et al., 2013; Miles & Huberman, 1984; Saldaña, 2015; Strauss & Corbin, 1998; Weber, 1990). However, the latter it would imply breaking with the frontier of theoretical analysis and entering into the meanders of qualitative research. Such alteration required though a shift from the current descriptive-evaluative research purpose into an explorative one, and the further adherence to an interpretativistic philosophical stance instead of a functionalist or positivist approach toward the portrayal of model’s evolution and adaptability to societal mutations. Yet, the latter consubstantiates another avenue for continuing this research toward more subjective approaches to theory development, as further described below.
Recommendation for Practice and Future Research
The methodological design followed is grounded on the integrative review process due to its recognized intrinsic virtues for reviewing theories, and for its flexibility to incorporate non-experimental studies (Souza et al., 2010; Whittemore & Knafl, 2005). However, new studies covering the topic while using other sources and extending its breadth to empirical studies is a natural step forward.
Iterations to this research, may comprise thus of subsequent endeavors either theoretical, empirical and/or hybrid, mono (quantitative or qualitative), multi or mixed-methodologies directly applicable to this case-model or applicable even to other seminal models (or crossed-observation) attempting to grasp its lifetime or evolutionary path to adapt to environmental circumstances, or comparing them in pairwise manner.
In this context, spinoffs of the latter can be also initiated with a micro focus on specific conceptualizations within a model, or nuclear focus on single attributes of a construct. For instance, looking at entire models as Dunning’s (1980, 2001) eclectic paradigm and observing the endured utility of the overall macro advantages (alias OLI factors), or focused on rather specific or sole concepts as the Sarasvathy’s (2001) principle of affordable loss as a component of the effectuation process, and/or on singly-focused into an attribute as “centrality” or “exclusion” within the respective concepts of network affiliation and liability of outsidership. Despite these latter suggestions on further IB/IG research, it ought to be emphasized that this methodological approach allows the extension of the research framework to other fields both social and natural sciences. In fact, the integrative review process is indeed a methodological tool widely used for reviewing literature in the health and medical science as deeply grounded on Cochrane’s EBP (Souza et al., 2010; Whitehead, 2013).
The replication of this research is of great importance for strengthening the context and usefulness of classical, contemporary, and neo-contemporary theorizations, and furthermore, for drawing a clear distinctive line between the staticity of inert conceptions and frameworks in time, and the rejuvenated ones which endure due to its activation, by the philosophical debate surrounding its ontology, evolutionary thinking-system and rationale, outer interest of scholars and practitioners on its reasoning, and subsequent managerial application to international decision and behavior guidance.
Furthermore, the emerging importance of international capabilization strategies within the firm and the formation of international OCs (argued in the case-model), in the context of IBs, appeals for further theoretical developments on the crossbreed of environment analyzability, internationalization and DC’ diffusion.
Footnotes
Declaration of Conflicting Interests
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The author(s) received no financial support for the research, authorship, and/or publication of this article.
