Introduction

Human resources potential, especially among scientists, is the most significant resource for building innovative and digital economies in certain countries. Necessary experience in evaluating the quality of scientific brainpower implies the investigation of different types of scientific mobility. These studies include analyses of mobility influence on scholarly output of researchers, organizations or countries; detection of driving forces of scientific mobility; registration of correlation between the fact of mobility and career progress of researchers; detection of the dependence of gender and nationality on mobility or impact of mobility on emerging research networks and collaborations. Thus, in recent years, the phenomenon of scientific mobility has attracted the attention of an increasing number of researchers in various fields of knowledge—scientometrics, sociology, economics, psychology, ecology—due to the increasing importance of scientists mobility in the context of science globalization and the growing number of inter- and multidisciplinary research. Since 2007, research on this topic has been published annually, just as the number of such studies is rapidly growing.

In the present work, an attempt is made to systematize the accumulated experience of work in this direction. This study continues the authors' previous analyses in respect to scientific mobility (Gureev et al. 2019), scientists career progress (Mazov and Gureyev 2015), as well as the impact of scientific policy on the scientists effectiveness (Guskov et al. 2018; Guskov et al. 2016; Guskov et al. 2017). Current work aims to identify general trends in scientific mobility at the world level according to the literature data over the past 30 years. The work does not purport to cover the full range of publications, the number of which increases significantly from year to year. Meanwhile, the number of reviews, especially bibliometric ones, and synthesis articles in scientific mobility is negligible (Ackers and Gill 2009; Appelt et al. 2015; Fernandez-Zubieta et al. 2015), with the part of the reviews are devoted to individual regions (Crossing Borders—Obstacles and incentives to researcher mobility2014; Ushkalov and Malakha 2011; Shmatko and Kachanov 2011), specific topics (Siekierski et al. 2018) or specific properties of mobility, e.g. impact on economies (Faggian et al. 2017).

Therefore, this study may partly fill some gaps in knowledge on scientific mobility, e.g., detailing the main properties of scientific mobility as opposite to inbreeding; detecting and typing significant topics concerning scientific mobility; analyzing dynamics of research topics based on bibliometric analyses to highlight the most relevant directions at the moment; reviewing current approaches to study scientific mobility, and, finally, specifying a range of open problems regarding mobility to be studied.

The paper is organized as follows: In the rest of the Introduction section, the general characteristics of scientific mobility and its differences from inbreeding are considered and the main stages of the development of scientists mobility in the 20–21 centuries are outlined. Further, scientific mobility is considered as an object of research interest: mobility types, research subjects, modern research methods have been identified. The motivations of mobile scientists are classified from different positions and the impact of mobility on scientific productivity is estimated.

General characteristics of scientific mobility: mobility and inbreeding

In our study, the term “mobility” is thought of as a paradigm in the sociology of science that investigates the movement of researchers between regions and countries and consequences of that movement on the development of science, regions, and mobile researchers. Many authors use the terms “mobility” and “migration” indiscriminately and interchangeably (see, for example, Moed and Halevi 2014; Trippl 2013) and note that changes in the patterns and motivations of researcher mobility blur the boundary between migration and mobility (Fernandez-Zubieta et al. 2015). Sometimes migration associates with social integration into a new society and thus with permanent nature of work abroad, while mobility implies temporal movement (Mendoza et al. 2020; Ackers 2005). However, both terms are applied to return movement of scientists to their home country and in this case, the fact of movement is always temporal, e.g., “return migration” (Murakami 2014) or “return mobility” (Baruffaldi and Landoni 2012). Eventually, we preferred to follow Mahroum (2000a) who seems to consider mobility as a social concept in science, whereas migration as just a physical movement.

At the global level, mobility generally produces positive results for the generation, accumulation, and dissemination of scientific knowledge (De Filippo et al. 2009; Jöns 2007), establishment of international cooperation among scientists (Murakami 2014; Trippl 2013) and the career development of researchers. Mobility contributes to the creation of new scientific centers of attraction, developing further scientists mobility and thus being a self-sufficient system (Mahroum 2000b).

According to a large-scale study by Franzoni et al. (2012, 2015) covering 16 leading countries and providing a general overview of international mobility, up to 40% of scientists are immigrants, and another 40% of them maintain ties with their home countries, facilitating the transfer of advanced scientific developments to their home countries. The participation of mobile scientists in international projects is higher by 13.8%, and that of returning scientists—by 7.4% compared to non-mobile researchers (Scellato et al. 2012).

Mobility is most developed in the United States, as it is a significant part of scientific policy, and the share of mobile scientists is from 80 to 90%, although it is noted that most of it falls on domestic mobility (Horta et al. 2010; Payumo et al. 2018). More than 40% of researchers in the United States are from other countries, and in some disciplines, the proportion of scientists who defended their Ph.D. theses in the United States exceeds half (Payumo et al. 2018; Scellato et al. 2012; Van Noorden 2012). Up to 30% of researchers who patented their inventions in this country are foreign mobile scientists (No and Walsh 2010). Up to a quarter of foreign scientists in the United States in the early twenty-first century were from the European Union (Ivancheva and Gourova 2011).

Mobility is contrasted with the concept of academic inbreeding,Footnote 1 or endogamy (Sivak and Yudkevich 2012) (terms borrowed from biology), involving the work of the researcher in the same organization in which they were educated (Horta 2013; Inanc and Tuncer 2011; Sivak and Yudkevich 2012). Inbreeding is generally evaluated negatively, but in some cases, there is a positive effect, mainly for the researchers' career. In general, inbred scientists have lower scientific productivity, and in organizations with a predominance of inbreeding, there is violation of research transparency principles, inconsistency of training courses with international standards, emergence of spheres of influence of individual researchers. In some cases, however, the negative effects may be due to lower income of inbred scientists, greater scientific and teaching load, performance of administrative tasks by inbred scientists, which together puts them in unequal positions with mobile scientists (Sivak and Yudkevich 2012).

Inbred scientists are least motivated to work together with foreign colleagues, they have significantly fewer foreign co-authors in publications compared to mobile ones, including returning from abroad researchers, and publications in journals with lower impact factors (Scellato et al. 2012).

Countries with a high degree of inbreeding are China, India, Korea, Japan, Turkey, Mexico, Russia, and some European countries (Inanc and Tuncer 2011; Sivak and Yudkevich 2012). In this regard, a number of countries, such as Japan, China, Korea, and Spain, are developing programs to increase the scientists mobility (Cruz-Castro and Sanz-Menéndez 2010). At the same time, in most European countries, the tradition remains to form the scientific personnel structure of the organization from its own graduates (Horta et al. 2010).

A brief overview of the main stages of scientific mobility development

Modern mobility is considered from World War II, during which a massive departure of scientists from Italy and Germany to the USA was recorded. The next wave of mobility was in the 1960s when European (primarily British) scientists left for the United States. At the same time, the concepts of brain drainFootnote 2 and brain gainFootnote 3 (emigration and immigration of scientists) appeared suggesting only one winner in the struggle for the minds. Historically, the brain drain has been associated with the beginning of the cold war, which requires countries, potential adversaries, a significant concentration of the best scientists (Meyer et al. 2001).

Since the 1970s, scientists mobility implying the long term decisions of individuals to move to other countries was registered from developing countries to Europe, where currently, there is a program of the European Research Area aiming at improving the competitiveness of the participating countries of the European Union. One of the program objectives is to prevent the migration of European scientists to the United States (Morano-Foadi 2005), which, for more than half a century, represents the endpoint of mobility that is most advantageous for most scholars, surpassing many states in both the number of studies and their quality (Murakami 2014; Veugelers and Van Bouwel 2015).

The beginning of the 1990s was marked by a change in mobility flows, an increase in the number of mobile scientists and the emergence of a new concept of brain circulation (brain exchangeFootnote 4), which in particular is associated with the end of the cold war, economy globalization, fragmentation of production processes, as well as lower prices for transport costs (Ackers 2005; Cruz-Castro and Sanz-Menéndez 2010; Edler et al. 2011; Jonkers and Cruz-Castro 2013; Saxenian 2005). Since the deterrent of air travel prices has disappeared, a part of those researchers who previously did not find financial resources for this, joined the mobile scientists, due to which middle-level scientists were involved in mobility flows. It is also confirmed by the fact that the share of Nobel laureates among migrant scientists declined due to the increased number of middle-level mobile scientists (Hunter et al. 2009). Equally, there were more people who found an opportunity to return to their home country during this period (Ackers 2005). The role of temporary mobility is increasing, as well as the range of scientists movement directions is expanding. In contrast to the previous period, the new type of mobility has already had a positive effect on donor countries, mostly represented by small developing states (Ciumasu 2010; Meyer et al. 2001). There are emerging models and concepts of mutual benefits for recipient (acceptor) and donor countries. Another concept of “brain transfer and transformation” similar to brain circulation was offered in (Kim 2010) implying that transnational academic mobility results in the new flows of knowledge that could benefit both sending and receiving countries more easily than before.

At the turn of the twentieth and twentyfirst centuries, there is another change in the system of scientific mobility associated with the informatization of society and scientific processes, which resulted in the concept of brain networking.Footnote 5 The concept is based on the understanding that modern means of communication greatly simplify the task of knowledge sharing, which in most cases does not require the physical movement of scientists (Ackers 2008; Aksnes et al. 2013; Bolli and Schläpfer 2015). Brain networking, like brain circulation theory, implies mutual benefits for recipient and donor countries (Ciumasu 2010).

With the decline of the prevalence of brain drain phenomenon (which, it should be noted, was somewhat resumed due to the effect of the 2008 economic crises) and the increase of influence of brain circulation, as well as knowledge sharing through remote access technologies, the former type of mobility associated with moving to a permanent residence in another country is gradually replaced by a new type of temporary mobility, in which mobile scientists, after gaining experience in scientific work abroad, return to their home countries (Edler et al. 2011). In many ways, this is facilitated by the maintenance by mobile scientists of scientific relations with colleagues from their home countries (Baruffaldi and Landoni 2012). To a greater extent, this trend is typical of developed countries, such as Canada, Australia, and some European countries.

There has been an increase in the number of returning mobile scientists in some Asian countries. Thus, a high proportion of returning researchers is characteristic of South Korea and Taiwan: up to 79% and 60%, respectively (Jonkers and Tijssen 2008), returned to these countries after foreign internships. The return mobility of Chinese and Indian scientists, who, having received a first-class education and experience in the United States, organize research IT companies in their own countries, continuing to maintain scientific ties in the United States thanks to wide communication channels and at the same time making a significant contribution to the economies of their countries, is becoming more pronounced (Saxenian 2005). In addition to IT-specialists, there is a high proportion of mathematicians who returned to China (Dubois et al. 2014). It is important to note that in the 1990s, up to 96% of scientists who left China, and up to 86% from India, preferred not to return to their country. However, by the end of the 2000s, because of the policy aimed at creating conditions for the return of fellow scientists from Western countries in the universities of Beijing and Shanghai, the scientific composition of up to 70% consisted of university professors with experience of foreign work (Jonkers and Tijssen 2008). A notable feature of the activities of mobile scientists who returned to India and China is a departure from competitive models in research in favor of the search for new activities, which allows maintaining international cooperation at a high level.

At the same time, there is scepticism about return mobility when it comes to developing countries (except for China and India discussed before). Having moved to a country with more favorable conditions for living and working, scientists benefit from not changing their place of residence. In particular, in economic disciplines, up to half of foreign scientists who defended their Ph.D. theses in the United States, remain to live and work in this country (Van Bouwel 2010). Of the remaining half, only one-third return to their home country, and two-thirds find work in third countries. In the chemical sciences, only 9% of mobile scientists in the United States return to their home country, while women scientists return much less frequently; also, the probability of scientists returning after they reach the age of 50 is sharply reduced (Gaulé 2014, 2011). As a rule, mobile mid-level professionals who have not found the opportunity to stay in developed countries are more likely to return to developing countries (Van Noorden 2012).

Research data and methodology

For the analysis, we thoroughly studied several dozen papers metadata of which were found in the Scopus database by Elsevier over the last 30 years beginning from 1990. The data were extracted in November, 2019. The selection of this database was based on a number of its advantages as compared to other systems (Kotsemir and Shashnov 2017) despite some limitations (Selivanova et al. 2019) not critical for our study. A search query in Article titles, Abstracts and Keywords fields includes the following terms: “research mobil*”, “scientific mobil*”, “academic mobil*”, “mobile researcher”, “research migration”, “scientific migration”, and “academic migration”. After that, we added to the obtained sample of papers those citing key papers from the sample (with more than 20 citations). Then original papers and reviews were selected for further analyses. The next step included de visu observation of abstracts to (a) select relevant papers and (b) assign research topics to each paper for multiplex bibliometric analysis aiming at the detection of trends in scientific mobility studies. Since one paper may be attributed to more than one narrow topic (up to three topics to some papers were assigned), we used fractional count. While manually processing our sample, we used bibliometric approaches for formulating search queries and obtaining necessary sample of publications; comparative technique when investigating topics in research papers and methods the authors had applied in their studies; linguistic approaches to detect and combine synonymous terms and notions used by different authors.

This study analyzed only the mobility of scientists and academics, thus, leaving aside students mobility at the manual inspection stage. In total, 684 relevant papers were retrieved, of which 123 studies were devoted to students mobility, and 183 papers were out of the scope of our research although contained abovementioned search terms in the metadata, e.g., those devoted to research mobilization. Finally, 378 relevant papers were perused of which more than a quarter were discussed in detail in our paper. Access to the data is available on demand.

Scientific mobility as an object of research interest

In the study of such a complex phenomenon as mobility of scientists, who by virtue of science universality have been the most mobile category of all professions for many years (Baruffaldi and Landoni 2016; Kim 2010) with unique properties different from mobility practices in other professions (Bauder 2015), many parameters and variables are taken into account, as well as goals and objectives of the parties interested in mobility: scientists themselves, scientific organizations or universities, expert community, science-based companies, decision-makers, as well as individual countries (Ivancheva and Gourova 2011).

Since mobility is studied by experts in various scientific fields (economists, sociologists, scientometricians, environmental experts, etc.), they use a wide range of methods and approaches from their disciplines, as well as focus on certain aspects of mobility. Thus, economists focus on mobility, given the macroeconomic driving forces and labor market arrangement in the analyzed countries; sociologists consider the adaptation of mobile scientists to the society organization and culture of their chosen country and record the moments of the scientists career growth. Scientometrics researchers first and foremost investigate the effect of mobility on the scientific productivity of scientists, organizations, and countries; psychologists study the influence of scientists personal characteristics and preferences on the choice of new places of work. In the light of modern concerns on ecological issues, climate change, and environmental sustainability, a new trend in investigating scientific mobility has been established covering problems of reducing carbon emissions caused by intensive academic air travels.

Types of scientific mobility

To date, there are four main types of scientific mobility, which are the object of most studies of this phenomenon (Table 1).

Table 1 Types of scientific mobility and their main characteristics
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Listed in Table 1 types of scientific mobility may overlap. For example, a scientist’s moving to another country may be accompanied by a promotion, a change of research areas and be temporary. In this case, mobility will be international, temporary, disciplinary, and vertical.

Research subjects of scientific mobility: bibliometric view

In Table 2, we summarized the main research subjects of scientific mobility.

Table 2 Main research subjects in scientific mobility and their share in publication flow
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Figure 1 demonstrates rates of growth of research interest to each of the detected topics in time. There were only several papers before 2004, the regular studies stated after 2007, whereas the period of quick growth lasts from 2013 with a short break in 2016. The most developed topics in this period are Factors inducing scientific mobility and Impact of scientific mobility.

Fig. 1
figure 1

Dynamics of growth in the number of publications on scientific mobility in the Scopus database according to the searching algorithm described in the “Research data and methodology” section

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According to the detected main subject areas in scientific mobility, we constructed respective citation matrices to reveal the dynamics of research interest and trends in the development of one or another topic. It should be noted that in rare instances the year of citing paper precedes the year of cited paper due to expansion of early access mode. In total, 330 papers out of 378 papers from our sample were analyzed from a bibliometric viewpoint according to five main subject categories of scientific mobility (48 papers were attributed to small categories and thus omitted).

As it is seen from Table 3a, scientific mobility is being actively studied, especially in recent years. Factors inducing scientific mobility category is the largest topic. Table 3b shows that initial interest in this field was observed in 2004–2005, and since 2009 this topic has been permanently grown with citedness focusing on recent studies. Dynamics of 2018–2019 can be explained by either fading of this topic or edge effect. The second large topic refers to the impact of scientific mobility (Table 3c) with the most active year of 2013. This topic has been cited with the increased intensity highlighting the active development of research interest. Flows of the scientific mobility category (Table 3d) demonstrates mixed dynamics with several gaps in publication activity. However, this subject has been actively sited, possibly in the context of neighboring studies. Development of approaches to study scientific mobility seems to be cutting edge topic which has begun to be studied in the 2010s (Table 3e) possibly due to increased availability of simplification of a broad range of different scientometric tools. Key papers were published in 2013, 2014, and 2019; citedness has been increased with gathering force. The most significant studies on the history of scientific mobility (Table 3f) were published in 2009, and the research focus was on studies published in consequent years decreases. It seems that they have been cited in the context of investigations on adjacent topics.

Table 3 Citation matrices for analyzed papers on scientific mobility according to the Scopus database: A—General group; B—Factors inducing scientific mobility; C—Impact of scientific mobility; D—Flows of scientific mobility; E—Development of approaches to study scientific mobility; F—History of scientific mobility
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Fig. 2
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Top 10 most productive (left) and most cited (right) countries (fractional count)

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The most productive countries are English-speaking UK, USA, and Australia followed by Russia where the interest in scientific mobility greatly increased in 2018–2019 (Fig. 2). The impact of China and India very small, despite they are very active participants of scientific mobility processes. The most cited country is the UK.

The object of a significant number of studies is mobility in the field of education, as evidenced by a pronounced cluster of educational journals and book series publishing the results obtained: Higher Education, Journal of Studies in International Education, International Perspectives on Higher Education Research, Discourse—Studies in the Cultural Politics of Education, etc.

Development of approaches to study scientific mobility

Currently, the scientific mobility analysis uses a wide range of methods, which in themselves often become the subject of scientific analysis in relation to the mobility study (Table 4).

Table 4 Main methods of scientific mobility analysis
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Using any of these approaches, mobility assessment can be both quantitative and qualitative. For example, quantification will require a simple accounting of the number of publications or citations, whereas in qualitative assessment, the study can be conducted based on a sample of high-rank journals (Jonkers and Cruz-Castro 2013; Kim et al. 2009); equally, in qualitative mobility assessment, the sample can include the most authoritative scientists (Halevi et al. 2016; Hunter et al. 2009; Trippl 2013). In addition to publications, patents, and citations, the qualitative aspect of scientific productivity due to mobility can be measured in the number of international grants received by scientists, their participation in various scientific programs, contractual works, Ph.D. theses, etc.

Factors inducing scientific mobility

When considering different factors inducing scientific mobility, especially the motivations of mobile scientists, it is necessary to identify the pull factors in the host country, organization, or area of expertise and push factors in the home state, organization, etc. (Bloch et al. 2015; Ciumasu 2010; Mahroum 2000a). Motivation to change the organization or country largely depends on the living conditions of scientists, their age, profession, social and political situation in the country, culture, etc. (Baruffaldi and Landoni 2016). It should also be noted, that the reasons for mobility are not always easy to determine or predict (Aksnes et al. 2013), especially since the findings of mobility studies are sometimes contradictory (Aksnes et al. 2013; Halevi et al. 2016; Moed et al. 2013).

Professional and personal growth

The main motivations of mobile researchers are the desire to expand their own scientific horizons, as well as to learn new technologies and get acquainted with new ideas, while the material benefit often plays a less important role (Scellato et al. 2012). To a large extent, this statement applies to more successful scientists, for whom scientific reputation and connections may be more important than material benefits (Gaulé 2011), as well as to scientists from developed countries, where the basic material needs of scientists are already satisfied (Baruffaldi and Landoni 2016), and in the first place are self-realization, scientific curiosity, self-development associated with travel and acquaintance with new cultures (Ackers 2005).

Additional incentives for mobility can be the desire of scientists to improve their skills and competitiveness for a more successful career (De Filippo et al. 2009), credibility of the host organization, access to good equipment, possibility of commercialization of their scientific products, more interesting research topics, comfortable working conditions, and higher living standards (Ciumasu 2010).

Socio-economic reasons

The pursuit of higher income is a frequent cause of scientific mobility, with scientists choosing to relocate to find ways to reduce costs (Ackers 2008). With this motivation, researchers tend to migrate to a chosen country for permanent residence, where their mobility ends (Baruffaldi and Landoni 2012).

Economic factors as a driving force of mobility are inherent in scientists from developing countries (Ciumasu 2010), as well as from some European countries with signs of the economic crisis, e.g., Spain or Italy. Also, economic factors are more likely to explain the mobility of young scientists who do not have a family and are not related to the care of children and parents, and are less applicable to the explanation of the motivation of scientists moving with families.

Higher degree of scientific mobility is typical of countries similar in language and history. Often, we are talking about a state with a strong economy and its former colony, while the distance does not play a significant role (Gargiulo and Carletti 2014) (cf. also conclusions about the importance of the country's language in the work (Moed et al. 2013)). This applies equally to countries with a common border, such as Switzerland and Austria.

One of the driving forces of mobility can be instability, and mobility itself becomes largely associated with the personal initiative of scientists and with risk (Ackers 2005; Baruffaldi and Landoni 2016). In this case, we have to talk about forced mobility of scientists, which can be caused by the following reasons:

  1. (a)

    completion of training, employment contract, and the need to find a new job (Ackers 2008; Morano-Foadi 2005). A similar situation is observed, for example, in Germany, where academic mentors are interested in saving more capable and proven post-graduate students in their organization, while less successful researchers with a recently obtained degree are forced to make up the bulk of mobile researchers, not being able to stay in the institution (Bäker 2015);

  2. (b)

    brain overflowFootnote 6 due to the reduction of science funding, for example, in the countries of the influence zone of the former USSR, which also creates a situation of brain wasteFootnote 7 (Ackers 2005). Sometimes brain overflow phenomenon is registered in “mature economy” countries. For example, Mendoza et al. (Mendoza et al. 2020), revealed in their recent study that the academic labor market in Southern Europe is saturated; therefore, it forces scientists to move to other regions including less developed countries of the Global South. Based on the example of researchers from Italy and Spain, the authors concluded that these two countries lack good opportunities in the academic sector as compared to Mexican academia which is relatively open to foreign highly qualified arrivals, who widely use their social networks to consolidate themselves in a new scientific labor market (Mendoza et al. 2020);

  3. (c)

    the predominance of elderly people in science management personnel, because in this case, belonging to certain scientific groups and personal connections often become more decisive in the scientific career than the generally recognized indicators in the world community. This leads to the migration of young scientists who disagree with the current system of science management (Sivak and Yudkevich 2012). The same factor may prevent return mobility, in which mobile scientists wishing to return to their home country do not find such an opportunity. This situation, for example, is typical of the countries of the influence zone of the former USSR (Ackers 2005). Bureaucratic obstacles to career growth in the home country, cumbersome system of appointment to scientific positions, lack of a transparent system of financing research (Ackers 2005; Baruffaldi and Landoni 2012) are typical of, but not limited to, some developed countries, for example, Italy and Japan, in which the influx of foreign authoritative scientists is extremely low (Van Noorden 2012). In this case, more transparent and open systems begin to play a decisive role when scientists move (Pelizon 2002; Mendoza et al. 2020). At the same time, it was suggested that in such cases one should rather try to recognize the inefficiency of some systems of science management and correct them than make an unjustified bet on the development of scientists mobility, which in this case remains a half-hearted and artificial solution (Ackers 2008);

  4. (d)

    absence of the necessary conditions in the home country, in particular, infrastructure and equipment, for research and successful career development (Ackers 2005). This situation is typical, for example, of Italian scientists (Carrozza and Minucci 2014) and researchers from Russia (Shmatko and Volkova 2017);

  5. (e)

    system of scientist's work evaluation, in which mobility is a mandatory component. In general, there is an ineffectiveness of systems of state direct encouragement of researchers returning from abroad, because such an approach can stimulate the return of scientists with average abilities who, nevertheless, will find themselves in a more advantageous position in front of more qualified but not mobile scientists from their country (Baruffaldi and Landoni 2012).

Constraints to the development of scientific mobility

In the study of the motivations and incentives for scientific mobility, special attention should be paid to the constraints, while they can prevent both the initial movement of scientists, contributing to the inbreeding development, and the return of scientists to their home country (Bauder 2015; Musselin 2004).

The knowledge and experience of the mobile scientist may not be compatible with the rules and traditions of the new organization or unclaimed in it (equally this applies to mobile scientists who returned with new knowledge to their home country). Examples may include incompatibility of research topics or methods, knowledge of the science arrangement in the home country, etc., which leads to reduction in human capital (Bäker 2015). This is particularly evident in disciplines with a wide range of methodological guidelines, where a change of arrangement with different approaches to research may devalue the knowledge available to the scientist from the previous place of work and require significant adaptation to comply with the rules at the new place of work.

Mobile scientists may have their own assessment of certain scientific ideas and concepts, which does not coincide with their assessment in the new country, another terminology, which also necessitates the acquisition of additional knowledge in a new place (Barjak and Robinson 2008). To some extent, the presence of a co-author from the organization to which the mobile scientist is sent to work smooths out the noted obstacle, which reduces the risks of incompatibility of scientific experience (Bäker 2015). A lower risk of incompatibility is also inherent in scientists in disciplines with a high degree of standardization of research methods, in particular in the natural sciences (Jöns 2007; Morano-Foadi 2005; Musselin 2004). That is why, there is less mobility in the social sciences and humanities, as for research in these disciplines requires knowledge of local realities, history of the country, language proficiency, etc.

In connection with the above, it was noted (Ackers 2005) that scientists cannot be considered as a vessel filled with knowledge, which can be transported and used in a new place in the same ways: knowledge or technology acquired in one organization may not be applicable in other conditions (Harris 2004).

The loss of professional ties in the home country is a deterrent to return mobility (Ackers 2008; Morano-Foadi 2005). In addition, there is often a situation of suspicious and envious attitude of inbred scientists to returning mobile ones, which can stop the latter from returning to their home country (Ackers 2005; Ciumasu 2010).

The reasons that stop scientists from moving to another country are also cultural ties with their own country and intangible values that people use at home, a circle of friends, and family ties (Gaulé 2014). For these reasons, many mobile scientists refuse to associate mobility with migration, which implies social integration into a new society, preferring to talk about the temporary nature of their work abroad (Ackers 2005).

In addition, mobility may be prevented by difficulties in the reimbursement of foreign travel, especially for young scientists; the low significance of the fact of mobility for career growth in some countries; connectedness to housing and family; immigration laws, lack of transparent, standardized international rules of employment, duties in relation to the place of work in their own country, language barriers, age limits, concerns about the possible return, which may be difficulties with employment, difficulty in finding work for spouse, etc. (Ciumasu 2010). We should also mention the red tape conservative systems of science management in some countries. For example, in France, Germany, and the Netherlands, scientists are reluctant to leave their countries, and if they do, they return very quickly, because otherwise, they risk not to integrate into their native systems and not to build a career (Van Noorden 2012; Musselin 2004).

Impact of mobility on scientific productivity and consequent development of researchers, organizations, and countries

The impact of scientific mobility can be studied at the level of individual scientists, research collaborations, scientific and educational organizations, countries, regions, or scientific disciplines. At the same time, it is important to note that the question of what is the root cause and what is the consequence when considering mobility and related events in the career of a scientist, the productivity of organizations or countries (if we do not take into account those countries where mobility is an essential condition for a successful scientific career) remains open. The fixed advantages of mobile scientists can be explained by their initial talents, higher working capacity and productivity, which motivated them to mobility. Their subsequent high-performance indicators may be due to their personal advantages rather than the fact of mobility (Aksnes et al. 2013; Ciumasu 2010; De Filippo et al. 2009; Shmatko and Volkova 2017; Veugelers and Van Bouwel 2015).

Mobility impact on career growth and scientific productivity of scientists

Positive effects of scientific mobility

Since mobility involves changes in human (knowledge and skills of the scientist) and social capital (communication and collaboration), which have a major impact on the scientist career progress, the consequences of mobility will affect these two main categories differently. As a rule, mobility is expected to bring an increase in both human and social capital, although the result is often expected only in the long term (Bäker 2015). Human capital, i.e. familiarity with the subject, knowledge of literature in their discipline, knowledge of research methods, and methods of analysis, leads to a greater number of publications or improvement of their quality. Social capital, i.e. the scientists connections, their ability to quickly find out the necessary information from colleagues, leads to greater collaboration, an increase in the number of co-authors, and higher chances of publishing the research results.

Scientists who migrated abroad, as well as those who returned to their country after working abroad, are considered to be the main driving force in the development of science and technology (Meyer et al. 2001). They have broader international connections than scientists without international experience, and for science, there is an effect of greater openness of scientific systems and improvement of the research quality (Franzoni et al. 2012, 2015; Payumo et al. 2018). At the same time, mobile scientists, while working abroad, establish links not only with the researchers of the host country or organization but also with researchers from third countries and organizations with which they collaborated (De Filippo et al. 2009). Work abroad is also important in terms of acquiring or improving knowledge of foreign languages (Ivancheva and Gourova 2011), which is seen as a broader understanding of mobility, which also includes social, linguistic, cultural and intellectual components in addition to the basic—spatial (Meyer et al. 2001).

On average, mobile scientists work more often in international projects, have more foreign co-authors, are published in journals with higher impact factors, while these characteristics are more inherent in scientists who moved to a new country for permanent residence in comparison with those who returned home after foreign internships, and in the least—with inbred scientists (Ciumasu 2010; Scellato et al. 2012). Mobile scientists are more often published in international journals, while inbred scientists are mostly published in domestic journals (Horta 2013).

Jonkers and Tijssen found the dependence between the time a researcher had spent abroad and the number of papers he or she published in international collaboration (Jonkers and Tijssen 2008). The scientific productivity of mobile researchers in comparison with inbred ones is 15% higher on average (Horta 2013; Horta et al. 2010). The initial position of the mobile scientist is of high importance: the lower it is, the less likely the researcher is to find themselves in a higher-level organization, regardless of the number of their subsequent movements; whereas the starting position in a credible organization guarantees the scientist that their career will not end in an average-level institution (Gargiulo and Carletti 2014). It is noted that scientists from elite organizations move mainly to elite ones, while middle-level scientists prefer middle-level organizations (Deville et al. 2014).

The highly positive impact of mobility on the career growth of scientists and their scientific productivity is typical of many countries. In the United States, mobile scientists are significantly superior to the bibliometric indicators of the inbred ones, with a remarkable effect found: scientists who are mobile at the domestic level publish better articles, while internationally mobile scientists outnumber the previous group in terms of the number of publications (Payumo et al. 2018). Significant superiority in scientific productivity is demonstrated by Turkish mobile scientists in comparison with the inbred ones, whose h-index is 89% lower than that of mobile scientists; in addition, the career of mobile scientists from Turkey is on average 5 years longer than that of inbred scientists (Inanc and Tuncer 2011).

In general, mobile scientists who returned to their home countries show better results in their careers and productivity. For example, Argentine mobile scientists who have returned to their country have 43% more publications written in the international collaboration, as well as more publications in journals with high impact factors and as the first authors, in comparison with their non-mobile compatriots (Jonkers and Cruz-Castro 2013). Returning scientists make full use of the experience gained abroad, which is manifested in their publication "autonomy", in which the number of publications in high-rank journals does not depend on the presence of foreign co-authors (Jonkers and Cruz-Castro 2013). Returning to their home organizations, Spanish mobile scientists are moving faster up the career ladder, have a higher income and faster receive invitations to permanent positions in universities (Cruz-Castro and Sanz-Menéndez 2010), and also have statistically significant productivity advantages, expressed by the impact factor of journals, the average number of citations, a lower share of uncited papers, and a higher level of international collaboration (De Filippo et al. 2009).

Despite the predominance of positive effects of scientific mobility in some cases, it has negative consequences (Ackers 2008; Melin 2005).

Negative effects of scientific mobility

In the short term, mobility reduces social capital, as connections with former colleagues are often broken, and the establishment of scientific ties in a new place takes time (Ackers 2008; Bäker 2015; Groysberg and Lee 2009; Morano-Foadi 2005; Smyth and Mishra 2014). Thus, Argentine scientists who migrated publish only 20–30% of their works in collaboration with former compatriots, while most of the research results are published in collaboration with scientists from other countries (Jonkers and Cruz-Castro 2013).

First of all, mobile scientists lose weak links (for example, former colleagues), which bring the greatest effect on productivity (Granovetter 1973), while strong links (co-authors) remain valid (Bäker 2015). Therefore, the bigger (in terms of employee number) was the researcher organization, which they leave, the greater the social capital depreciation will be observed in their mobility. The example of Argentine science shows that even when returning home, mobile scientists in rare cases actively cooperate with fellow countrymen, and previous strong ties with them are equated by weak ties from foreign countries in which scientists temporarily worked (Jonkers and Cruz-Castro 2013). German mobile researchers with a large number of co-authors and from large organizations in the short term when changing jobs are also less published in comparison with colleagues who have not changed the organization. At the same time, mobile scientists were initially less productive, because they were forced to move, unable to compete with more successful colleagues in their organization (Bäker 2015).

The specific situation with regard to mobile scientists is observed in Scandinavian countries. Since they have a high degree of inbreeding, mobile scientists who have returned from abroad face rejection of their international scientific experience; thus, up to 20% of returned scientists assess the fact of their mobility negatively (Melin 2005). In this case, scientists who have never left the country find themselves in a better position than mobile scientists, and state investment in mobility in these countries can be considered inappropriate.

The increased requirements for mobility and internationalization force researchers to choose international topics on which grants can be obtained more quickly, the results of which are easier to publish in high-rank journals, and ignore no less important regional topics, which puts researchers in an unequal position (Ackers 2008; Bäker 2015).

With various models of scientific mobility in different disciplines, some of which are not open to internationalization, and the computerization of many scientific procedures and processes that no longer require scientists to travel or relocate (Aksnes et al. 2013; Bolli and Schläpfer 2015), it is important to understand that mobility should no longer be seen as a necessary attribute of the success of scientists careers (Ackers 2008), which is still observed in a number of countries. At the same time, as in most other cases of formal metrics, manipulation is also possible here, which often takes into account the fact of changing jobs, internships, etc., but does not pay attention to the quality of these trips. Thus, Portuguese specialists with a Ph.D. degree from abroad were evaluated significantly higher than those who defended theses in their home countries, although the latter often had higher qualifications (Ackers 2008).

Mobility impact on the development of scientific organization, university or country

Positive effects of scientific mobility

Mobility brings the exchange of scientific experience, methodological settings, non-standard methods of solving problems in connection with the communication of scientists with different education, world view, and learning history. Thus, it is believed that mobile researchers develop transnational identity capital and a sense of multi-belongings (Kim 2010). On the contrary, inbred scientists have fewer incentives to exchange scientific information outside the walls of their organization, less likely to seek or cannot accept other from established in their organization approaches to research, have virtually no collaborators from other organizations, which generally leads to reduced scientific productivity (Horta 2013).

Mobile scientists are more preferable for admission to scientific organizations and universities due to greater objectivity during the competition, emergence of competition and, as a consequence, participation in the competition of a larger number of qualified employees (Smyth and Mishra 2014). It is noteworthy that at the beginning of their career, scientists go to work in institutions less prestigious in comparison with the organization where they were educated, which is very beneficial to employers and can improve the performance of the organization (Smyth and Mishra 2014).

In terms of bibliometric indicators (for example, the number of citations or the Hirsch index), both for mobile scientists and for organizations, the greatest effect is brought by internal mobility (i.e., scientists change in their own country), while mobility at the international level may not have a significant impact on productivity growth. An interesting fact is that the number of organizations in which mobile scientists worked is irrelevant, but the change of at least one affiliation has significant consequences (Halevi et al. 2016). When considering the European Union countries as a single state entity, Veugelers and Van Bouwel come to the same conclusions (2015).

In determining the economic benefits for a country or region, several parameters need to be considered: for example, in which country the researcher received a Ph.D. degree, i.e. which country paid for the specialist training (Ackers 2005); how much time the mobile scientist spent abroad because the host country is important to return the investment in the researcher, etc. As a rule, the scientific mobility impact on the development of national economies is assessed positively. Thus, in Germany, the duration and frequency of foreign scientific trips are directly related to the participation of mobile scientists in the work of technology companies, which through scientists have access to foreign technologies (Edler et al. 2011). At the same time, German scientists from universities are more mobile in comparison with researchers from scientific organizations but are less connected with technology companies.

Linking scientists from different countries benefits not only the host country but also the donor country (Scellato et al. 2012). Mobility is particularly important for the development of science and the economies of developing countries with low incomes provided that scientists who have gained experience abroad return (Gibson and McKenzie 2014). The example of Pacific island states shows the significant role of returning scientists in the dissemination of knowledge in their home country, the subsequent maintenance of international relations with other countries, as well as in the greater scientific productivity of mobile scientists, expressed in the number of international co-authors and more frequent visits to international conferences (Gibson and McKenzie 2014).

Mobile chemists who returned from the United States to their home countries maintain high rates of productivity, which has a significant impact on the development of research in these countries (Gaulé 2011). The significant role of the most successful mobile scientists who returned home is emphasized in the work (Trippl 2013), where the example of a large sample in various disciplines focuses on knowledge dissemination, establishment of scientific relations, as well as the contribution of mobile researchers to the industrial sector of their home countries.

Negative effects of scientific mobility

Under certain conditions, the mobility impact on the organizations development is negatively assessed, and inbreeding is considered to be more preferable, since trained personnel in the organization do not spend time on mastering the already known realities, unlike mobile scientists, but are directly engaged in research (Smyth and Mishra 2014). To some extent, this is consistent with the observation that inbreeding is justified in high-ranking organizations, but undesirable in medium-level institutions (Sivak and Yudkevich 2012).

The example of scientists from Austria, Germany, and Switzerland shows that mobility increases the productivity of only well-established scientists, but does not give anything to unproductive employees, and therefore the costs of promoting mobility are not fully justified (Bolli and Schläpfer 2015).

The effectiveness of state incentives programs for scientists mobility casts doubt on the alleged impact of the researchers return. Despite the repeatedly high rate of productivity of scientists mobile after returning home, the proportion of returned scientists is often very low.

The question of the ethical side of mobility, for example, in the medical sciences, seems to be significant. For example, the scientific migration of medical personnel and scientists from African countries, combined with their working conditions in developed countries, has led to significant shortages in African countries, making it difficult to combat many infectious diseases in the region (Scott et al. 2004).

Since 2017, a new cutting-edge trend in scientific mobility studies was detected assessing an impact of academician air travels on environmental sustainability since air travel has been recognized as an essential source of greenhouse gas emissions contributing to climate change. For example, the studies (Glover et al. 2017, 2018) concluded that the ambitions of academic institutions to reduce carbon emissions from air travel are discordant with broader policies and strategic orientations around international mobility. Another study conducted in New Zealand also reflects on traditional academic practice to be mobile and contemporary urgent need to decarbonize transport in order to solve the new problem of “climate hypocrisy” of high-carbon academic work-related travel (Hopkins et al. 2019). Some possible solutions include the development of virtual or synchronous types of mobility which are believed to be a good substitution for actual mobility (Higham et al. 2019).

Neutral assessments of the scientific mobility impact on researchers, organizations or countries

While some data point to the positive aspects of scientific mobility and others to its negative consequences, in some cases, there is no direct and proven link between the fact of mobility and scientists productivity, their career growth, dissemination of scientific knowledge, and the development of scientific organizations or universities.

From the point of view of career growth, it was revealed that in a number of countries, internationally known research teams are headed by inbred scientists. First of all, it is typical of Europe and the United States. Thus, in the field of economics, in the United States up to 86% of scientists have never been mobile (Van Bouwel 2010), in Spain, when taking a scientist to a permanent position, their publication activity has more weight than the fact of mobility, and in the United Kingdom, mobility has never been considered a prerequisite for career advancement (Morano-Foadi 2005).

A number of examples proves the lack of connection between mobility and indicators of scientific productivity. Thus, for a wide range of indicators (number of publications and citations, Hirsch and Egg indices), there were no differences in the productivity of mobile and non-mobile researchers from Australia (Smyth and Mishra 2014) or Canada (Wynes et al. 2019). The analysis of the number of Argentine mobile and inbred scientists publications also showed no statistically significant differences, although mobile scientists are more likely to be published in higher-rank journals (Jonkers and Cruz-Castro 2013), which, however, may be due to their better command of the English language obtained while working abroad, rather than the higher quality of research (Jonkers and Tijssen 2008). There is no direct relationship between the mobility and scientific productivity of scientists from Germany, Austria, and Switzerland (Bolli and Schläpfer 2015), which may be due to the increased opportunities for remote exchange of information among scientists. There is no link between mobility and productivity in Spain (Cañibano et al. 2008), where at the same time, there is a link between mobility and career growth, as well as the dependence between the fact of mobility and higher quality research as compared to the quality of papers of inbred scientists. Neutral or negative scientific mobility is traditionally assessed in Sweden (Melin 2005) and Norway (Aksnes et al. 2013) where the inbreeding degree is high.

We should also point out the lack of connection between the indicators of scientific productivity and mobility among highly respected scientists. The sample of the most authoritative physicists, including Nobel laureates, analyzed by Hunter et al. is an indicative example: although the authors demonstrated a high degree of mobility among the studied group (half the instances), they also demonstrate a lack of superiority in productivity (expressed by the number of citations and the Hirsch index) of mobile scientists over the non-mobile ones (Hunter et al. 2009). Similar conclusions are demonstrated by Trippl (2013). The analysis of a wide international sample of established mathematicians shows that since mobility is mainly observed between pairs of countries (for example, the USA—Canada) and is uniform: both in the scientists number and their authority, there is no mobility impact on the scientists careers, their performance indicators or scientific achievements of countries are not observed (although the fact of mobility may be useful for novice mathematicians) (Dubois et al. 2014).

Conclusions

Modern scientific mobility has a long history since from 1940-th, during which there were several paradigm shifts (brain drain/brain gain, brain exchange, brain networking), caused by the political, social, economic, and technological reasons.

In recent years, this phenomenon has become particularly important in the development of science and technology, in the career of scientists and in the dissemination of scientific knowledge, which is confirmed, among other things, by the increased interest in the study of mobility both in the scientific community and the research governing bodies. The main reasons for the mobility growth is the very international specificity of the researchers work, which distinguishes them from other professions, increased transport opportunities, and increased importance of interdisciplinary research, stimulating scientists to be mobile. Modern mobility due to the development of information and communication technologies takes such forms as brain networking and synchronous mobility.

Since 2007, the bibliometric analysis shows the sustainable growth of papers concerning scientific mobility issues. The most popular topics are factors, inducing scientific mobility (38%), and impact of scientific mobility (38%), whereas there are not as many publications on flows of scientific mobility (15%) and development of approaches to study it (5%). The first large cluster of papers investigates reasons or factors inducing mobility including different motivations of researchers to move, gender and geographical factors, as well as research policy in a certain region. Oppositely, another large cluster of papers studies the impact of scientific mobility on a variety of items including scholarly output, career trajectories, dissemination of knowledge, research collaborations, etc. Citation analysis revealed that papers from both large topics have been cited with the increased intensity, especially the most recent studies, highlighting the active development of research interest to these issues. Development of approaches to study scientific mobility seems to be cutting edge topic which has begun to be studied in the 2010s with citedness has been increased with gathering force. The most used methods include analysis of CVs, different kinds of surveys and questioning approaches, and scientometric techniques. Besides, nowadays a new trend in investigating scientific mobility has been established covering problems of reducing carbon emissions caused by intensive academic air travels.

We believe that scientific mobility still could be considered as an emerging area of research having a number of problems to be explored:

  • Although the personal motivation of mobile researchers has been well studied, the impact of political, economic, and social changes in individual countries and regions on the movement of scientists will continue to be relevant topics.

  • What is the root cause and what is the consequence: the scientific mobility brings the success or the initial talents, higher working capacity and productivity motivate the researcher to search for opportunities in new locations.

  • How does the scientific mobility improve the knowledge and technology transfer between developed and developing countries, how does it affects national science&technology sector and research policies.

  • What is the impact of new technologies that are greatly improved the communications of scientists over the world and, to some extent, impede the development of academic mobility.

  • Constantly increasing the internationalization of research, mobility support programs, and the introduction of research-performance based policies in some countries create the prerequisites for the development of synchronous mobility and this phenomenon has been little studied up to now.

  • The development of methods to study scientific mobility probably will be based on the involvement of new data sources, which contain the information about social, economic, and politic events, affecting the research infrastructure and environment.

In most cases, the researchers mobility has a positive impact on the scientific organizations development, the growth of their scientific productivity, and career success of researchers. However, scientists cannot be considered as a vessel filled with knowledge, which can be transported and used in a new place in the same ways: knowledge or technology acquired in one organization may not be applicable in other conditions. In some cases, there are certain shortcomings, which, nevertheless, are analyzed, can be systematized and with the right decisions can be overcome.