AbstractDixidae (Diptera). All records of this family from the territory of Croatia are summarized, including previously unpublished data. Collections contained six species of Dixa Meigen – D.dilatata Strobl, D.maculata Meigen, D.nebulosa Meigen, D.nubilipennis Curtis, D.puberula Loew, and D.submaculata Edwards, with Dixadilatata reported from Croatia for the first time. Information relating to the ecoregions in which species were found and specific species traits are provided. Compared to neighbouring countries, the Croatian species assemblage is most similar to the fauna of Italy and least similar to that of Serbia and Montenegro.Invertebrate surveys in Croatia conducted between 2005 and 2018 included 39 sampling sites yielding bycatch samples of  Dixidae, or meniscus midges, are one of the smallest families of Diptera in Europe, with only two genera, Dixa Meigen and Dixella Dyar and Shannon, and 32 species recorded  and the Pannonian lowland (ER11) (d (ER11) , and forSpecimen records. This paper is based on unpublished data from our own research and published data gleaned from the literature. Each record was georeferenced using ArcGIS software. The literature used for identifications included Limnofauna Europaea ; new records . All the sites and their numbers are listed in Table New records. • 1 larva; Stream Sartuk, NP Plitvice (22); 10 Sep. 2009. •1♂; Roški Slap, Krka River, NP Krka (37); 29 Mar. 2011; M. Ivković leg.Remarks. This species is newly recorded from Croatia.Literature references. • tufa barrier Novakovića Brod, NP Plitvice (Plitvice  (24) • tPlitvice  (25) • tPlitvice  (27) • uPlitvice  (29) • uPlitvice  (30).New record. • 1 larva; Dubočanka, Papuk Mountain (14); 9 Sep. 2009.Literature references. • River Korana in Korana village, NP Plitvice (Plitvice  (21) • SPlitvice  (23) • tPlitvice  (24) • tPlitvice  (25) • tPlitvice  (27) • uPlitvice  (30) • RPlitvice  (37) • SPlitvice  (38).New records. • 1 larva; Bošćak Stream (1); 15 Apr. 2010• 1 larva; Bistrec Stream (3); 13 Jul. 2010 • 33 larvae; same site; 16 Sep. 2010 • 1 larva; same site; 18 May 2016 • 48 larvae; Kotoribski kanal (4); 18 May 2016 • 2 larvae; Plitvica, Upper Reach (5): 25 May 2009 • 10 larvae; same site; 13 Jul. 2010 • 13 larvae; Djedovica by Rupnica, Papuk Mountain (9); 9 Sep. 2009 • 1 larva; River Duboka rijeka, Papuk Mountain (12); 9 Sep. 2009 • 1♀; same site, 18.ix.2012, M. Ivković leg. • 1♀; Dubočanka, Papuk Mountain (14); 18 Sep. 2012; M. Ivković leg. • 1 larva; River Riječina, upper reach (15); 23 Sep. 2009 • 1 larva; Velika Belica (16); 24 Nov. 2009 • 1 larva; Headwater of Dobra River (17); 24 Sep. 2009 • 8♂ and 3♀; Mrežnički Brig, Mrežnica River (19); 10 Sep. 2011; M. Ivković leg. • 6 larvae; River Dretulja, Plaški (20); 9 Oct. 2009 • 3 larvae; Lake Kozjak, NP Plitvice (26); 18 Jul. 2018 • 15 larvae; same site; 16 Sep. 2016 • 4 larvae; River Kosovčica (33); 12 Jun. 2012 • 2 larvae; River Krka above the mouth of River Kosovčica (35); 19 Sep. 2012 • 2 larvae; River Krka below the mouth of River Kosovčica (36); 20 Sep. 2012 • 1♂; Roški Slap, Krka River, NP Krka (37); 29 Mar. 2011; M. Ivković leg. • 2♂; same site; 28 Apr. 2011; M. Ivković leg. • 1♂ and 1♀; Čikotina Lađa, River Cetina (39); 2005; M. Ivković leg.Literature references. • River Korana in Korana village, NP Plitvice (Plitvice  (21) • RPlitvice  (37).New record. • 1♀; Kosovčica Spring (32); 18 Nov. 2010; M. Ivković leg.Literature references. • River Korana in Korana village, NP Plitvice (Plitvice  (21) • SPlitvice  (23) • tPlitvice  (24) • tPlitvice  (25) • tPlitvice  (27) • mPlitvice  (28) • uPlitvice  (29) • uPlitvice  (30) • sPlitvice  (31) • RPlitvice  (37).New records. • 2♂ and 1♀; Spring Šumi, Zagorje (6); 15 Jul. 2014; M. Ivković leg. • 1♂; same site; 9 Oct. 2014; M. Ivković leg. • 1 larva; Kraljevec, Medvednica Mountain (8); 21 Jun. 2006 • 1♀; Brzaja, before N. Zvečeva, Papuk Mountain (10); 14 Jun. 2012; M. Ivković leg. • 1♀; Stream Kovačica, Papuk Mountain (11); 14 Jun. 2012; M. Ivković leg. • 3♂ and 5♀; Dubočanka, Papuk Mountain (14); 13 Jun. 2012; M. Ivković leg. • 1 larva; River Bukovačka Dobra (18); 18 Jun. 2006 • 1♂ and 1♀; Stream Plitvica, NP Plitvice (23); 28 Jun. 2007; M. Ivković leg. • 1♂; tufa barrier Novakovića Brod, NP Plitvice (24); 29 May 2007; M. Ivković leg. • 2♂ and 1♀, same site, 28 Jun. 2007; M. Ivković leg. • 1♀; tufa barrier Kozjak-Milanovac, NP Plitvice (25); 28 Jul. 2007; M. Ivković leg. • 2♂; tufa barrier Labudovac, NP Plitvice (27); 29 May 2007; M. Ivković leg. • 1♀; Roški Slap, Krka River, NP Krka (37); 17 Sep. 2010; M. Ivković leg. • 1♂; same site; 16 Dec. 2010; M. Ivković leg. • 3♀; same site; 29 Mar. 2011; M. Ivković leg. • 84♂ and 43♀; same site; 28 Apr. 2011; M. Ivković leg. • 3♂ and 6♀; same site; 29 May 2011; M. Ivković leg. • 1♂; same site; 13 Oct. 2011; M. Ivković leg.Literature references. • tufa barrier Novakovića Brod, NP Plitvice (Plitvice  (24) • tPlitvice  (25) • mPlitvice  (28) • uPlitvice  (29) • uPlitvice  (30) • sPlitvice  (31).New records. • 2 larvae; River Reka, upper reach (7); 8 Nov. 2009 • 2 larvae; Kraljevec, Medvednica Mountain (8); 21 Jun. 2006 • 1 larva; River Orašnica (34); 16 Jul. 2009 • 1 larva; River Krka above the mouth of River Kosovčica (35); 19 Sep. 2012.Dixa (Table Dixanebulosa is found at the greatest number of sites (25) while Dixadilatata was the rarest, found only at two sites. All six species occur in the Dinaric western Balkan (Ecoregion 5), while four species occur in the Pannonian lowland (Ecoregion 11). All recorded Dixa species are widely distributed in Europe . Available seasonal phenological data (Table Dixapuberula and Dixasubmaculata Edwards) are multivoltine and present all year round. Dixamaculata and D.nebulosa occurred from spring through autumn. Dixanubilipennis was only collected during summer.In total six species of xa Table  are recoxa Table , Table 1of sites 5 while Dn Europe  are now of sites 5 while DDixa, while Serbia and Montenegro each have only a single recorded species, Dixanebulosa (Fig. Dixa fauna of Croatia is most similar to that of Italy followed by Hungary, whereas it is least similar to that of Serbia and Montenegro (Table Italy and Hungry have seven and five, respectively, recorded species of osa Fig. . The Sørro Table . These rFauna Europaea (D.maculata, D.nebulosa, D.nubulipennis, D.puberula, and D.submaculata. Herein, we report Dixadilatata as new to the dixid fauna of Croatia.Comparing our list of Croatian species with published records in the Europaea  revealedDixa yet to be recorded, and, because of the high endemicity of the Dinaric area (Diptera (Dixa may yet be found. In the future, collecting should be focused not only on lotic habitats but also on lentic habitats so that Dixella species can also be studied.All the recorded species have a wide European distribution and none is restricted to Croatia or to the Balkan Region. There may be a few more species of ric area  and espe(Diptera , it is p


This review aimed to discuss the correlates of the double burden of malnutrition through the socio-ecological model (SEM); (2) Methods: The PubMed database was systematically searched for peer-reviewed articles related to the double burden of malnutrition. Information on correlates of the double burden of malnutrition was extracted for analysis and discussion in alignment with the levels of the socio-ecological model.; (3) Results and Discussion: The correlates of the double burden of malnutrition identified from previous literature were: Race/genetics; maternal short stature; breastfeeding status; low maternal education; family size; household food security; household dietary diversity; and rural and urban settings. In the absence of evidence linking factors in a certain level of the SEM and the double burden of malnutrition, we employed correlates of overweight status and obesity to complete this narrative. Potential intervention strategies were proposed in alignment with the targets and settings identified, based on the socio-ecological approach; (4) Conclusions: The double burden of malnutrition is a public health phenomenon associated with a variety of socio-ecological determinants. An integrated approach is needed to address the root causes of malnutrition in all its forms, and at all life stages. The tre0 kg/m2) . Moreovese BMI > 0 kg/m2 [Obesity does not only affect developed countries; developing countries also suffer from obesity at an increasing pace . Data frIn developing nations, nutrient deficiencies manifesting as under-nutrition  persist, while the problem of overweight people and obesity has increased rapidly. Reporting on studies in six developing countries, the Food and Agriculture Organization (FAO) of the United Nations  referredExisting studies have defined the double burden of malnutrition at the individual, household, and population or country level . At the Most studies in the peer-reviewed literature describe the double burden of malnutrition at the population or country level, where a portion of the population suffers from undernutrition while another part of the population faces the problem of over-nutrition. At the national level, the double burden of malnutrition has been identified in developing countries such as in South Africa , Brazil As seen in The increasing prevalence of double burden of malnutrition across studies in the same country highlights the emergence of this problem . Data frIn 2005, a Guatemalan study revealed that the prevalence among child and mother pairs consisting of stunted children and overweight mothers was 16% . This nuDue to the apparent complexity of the double burden of malnutrition, we sought to describe and frame the problem in a logical, comprehensible manner that would enable policy makers to take necessary action. One approach widely used to describe such a complex phenomenon is the socio-ecological model (SEM). The socio-ecological approach to public health originated from the concept of the ecology of human development introduced by Bronfenbrenner in the 1970s . He arguOur literature review will offer a new insight into correlates of the double burden of malnutrition through the use of the socio-ecological model. This is a good starting point, because it identifies significant correlates and characteristics of the target population most in need of intervention. With its multiple levels and interrelationships, we believe the socio-ecological model is best for capturing the complexity of the double burden of malnutrition that is hampering populations in developing countries. The SEM’s underlying premises arguably are suitable for examining the phenomenon of double burden of malnutrition and interrelations among correlates, or determinants, on multiple levels. Hence, this review aims to summarize present knowledge about correlates of the double burden of malnutrition based on the socio-ecological model (SEM).In this literature review, we did not limit ourselves to specific levels and measures of the double burden of malnutrition, but placed equal emphasis on correlational evidence of this phenomenon. Relevant studies were systematically identified using a structured search within the PubMed database. Initial keywords searched were “double burden of malnutrition,” “dual burden of malnutrition,” “stunted child or overweight mother,” and acronyms related to the double burden of malnutrition such as DBM, SCOWT, or SCOM. We did not impose date restrictions, but limited our search to articles published in English. Reference lists from identified articles were examined (hand searches) for additional relevant studies missed by electronic database indexing. In terms of the type of the study, we did impose restrictions for study inclusion criteria in the analysis: The minimum level of evidence was a cross-sectional study; for a study to be relevant and, therefore, included, we required reporting of risk factors or protective factors for the double burden of malnutrition. Articles were excluded if the study was not conducted in developing countries. We conducted a systematic review of all articles published between January 2000 and January 2016. As of 19 January 2016, the aforementioned keywords turned up 1806 articles; however, only 15 of those articles contained correlates of the double burden of malnutrition identified in this review. The records were screened at the abstract level. Then, in July 2019, we updated the literature review with additional 7 relevant articles published after January 2016. As seen in Evidence shows that racial differences are associated with different rates of the double burden of malnutrition. Studies among Latin Americans revealed that being from the indigenous population was associated with higher risk. The prevalence of coexistence of maternal central adiposity and child stunting (MCA) in a Mexican population was higher among indigenous families . A studyMaternal health status and lifestyle, including both under- and over-nutrition arguably play a key role in programming metabolic risk in the offspring. In the late 1980s, Barker postulated that maternal nutritional condition during pregnancy can “program” the fetus for the development of chronic disease later in life . The fetThe double burden of malnutrition may provide support for the Barker hypothesis. Embryonic and fetal growth starts with proliferation, organization, and differentiation of the embryonic cells, followed by continued growth and functional maturation of the different fetal organs and tissues . This prBreastfeeding behavior has been found to protect against the double burden of malnutrition. In Indonesia, for a child who was breastfed, the odds of having MCDB was lower (OR = 0.84) compared to a child who was not breastfed (95% CI = 0.81–0.87) . The prop < 0.0001) [p = 0.01) and stunting (p = 0.019) [Ample evidence shows that short maternal stature is associated with child stunting, but evidence associating it with double burden of malnutrition was limited. A study in Brazil revealed that children of mothers who have a height less than 145cm had lower height-for-age Z-score (HAZ) than children of mothers more than 160 cm tall = 0.019) . In anot= 0.019) . Althoug= 0.019) ,60,61,62 . In ano= 0.019) .p < 0.05) [Similar to other correlates of double burden of malnutrition on the interpersonal level, maternal education was extensively studied as a predictor of child stunting, but was rarely studied as a predictor of double burden of malnutrition. Low maternal education has been linked with child stunting . Further < 0.05) . AlthougOne correlate of the double burden of malnutrition identified in the interpersonal level was family size. A study in an Argentinian population revealed that households with SCOWT tended to have more people living in the house . Large fWhile food insecurity was largely associated with child stunting ,17, evidp < 0.001), height-for-age Z-score (p < 0.005) [At the interpersonal level, a correlate of the double burden of malnutrition was partly represented by household dietary diversity. Some studies have shown that dietary diversity score (DDS) is positively related to weight-for-age Z-score (< 0.005)  and that< 0.005) . A study< 0.005) . It is a< 0.005) . In cont< 0.005) .Among the diverse food groups, foods containing high growth-promoting nutrients are essential to prevention of the double burden of malnutrition. A cross-sectional study in an Indonesian population showed that when consumption of the “high-animal products” was in the highest quartile, the risk of maternal-child double burden decreased  relative to those in the lowest quartile . The higThere is a dearth of evidence associating double burden of malnutrition with a shift in the workplace environment, with limited opportunity for physical activity. Changes in the environmental settings and type of work were reported to be a significant factor in the increasing rate of overweight condition and obesity . The amoIn the socio-ecological model, both rural  and urbaContrary to the popular belief regarding an “obesogenic” environment being largely embedded within urban settings, evidence from Latin American countries suggests that double burden of malnutrition was more prevalent in rural settings. A study about the double burden of malnutrition in Columbia showed that the prevalence of child stunting was highest in rural areas . SimilarThe double burden of malnutrition is believed to affect populations undergoing economic improvement, as opposed to low-income populations. The association between the double burden of malnutrition measured as SCOWT and per capita GDP supports the hypothesis that economic development increased the likelihood of SCOWT . AnalysiTo the best of our knowledge, no studies have specifically addressed food policy as correlates of the double burden of malnutrition. With the open-market policy and globalization, some argue that the power of transnational industries will affect the pace of nutrition transition in countries with flourishing economic development. Furthermore, as countries undergo the nutrition transition, the problem of double burden of malnutrition is likely to increase. The increases in obesity for the last 3 to 4 decades in almost all countries seem to be driven mainly by changes in food composition and availability  through The problem with an influx of relatively affordable energy-dense foods has been negated in several countries through food taxation policy. Edible oil-pricing policies were changed a number of times in China between 1991 and 2000 to influence dietary composition toward less fat . Other fPopkin has argued that the double burden of malnutrition in one household is related to urbanization . As urbaUsing the socio-ecological model, we suggest several targets and settings for an intervention aimed at the double burden of malnutrition . First, At the individual level, we argue that the mother plays a key role in preventing the double burden of malnutrition for herself and her family. Hence, empowering women to take care of the household in the direction that supports healthy food choice and availability is seen as critical ,77. EvidProviding intensive 12-week nutrition education in obese/overweight mothers with stunted children was successful for engaging mothers in physical activity and also improving children’s fruit, vegetable and animal protein consumption in Indonesia ,79,90. EAt the interpersonal level, inequalities in food distribution within the household should be minimized and healthier food for all should be promoted. A study in Indonesia revealed that residing in an urban location increased intra-household nutritional inequality . SimilarAt the organizational level, modernization has led the workplace to be more sedentary than the previous decades . Some stAt the community level, changes in the built environment are inevitable due to economic development and mechanization in both rural and urban areas. The double burden of malnutrition was reported in both of these areas, partly due to the increase of obesogenic environment . In ruraThe indigenous community requires special consideration because of the peculiar pattern of correlates of double burden of malnutrition. Interestingly, indigenous populations in rural Latin America such as Mexico  and GuatAt the policy level, several countries have implemented a taxation policy for energy-dense foods such as vegetable oil and soft drinks. This policy should be maintained and expanded to other unhealthy foods to reinforce community-level interventions to address healthy eating. For example, the Chinese policy to increase the price of edible oils might trigger a shift in dietary composition from fat towards proteins and complex carbohydrates .To prevent a further influx of urbanization, rural areas should be developed equally with, if not more than, urban cities. Countries undergoing urbanization in Africa, such as Kenya  and EgypEconomic development experienced in some middle-income countries provides a good opportunity for food security, but food security assessed as the availability of food in quantity alone might not be adequate to prevent the double burden of malnutrition. Unlike households facing only the problem of child stunting, households undergoing the double burden of malnutrition seem to have the capacity to access food, but have a problem choosing healthy foods that are lacking within the household. Food security in these households might promote the double burden of malnutrition when a household is spending money on less nutritious food. Consumption of energy-dense foods lacking in growth-promoting nutrients does not prevent child stunting but instead may lead to excess weight gain, overweight status and obesity. Therefore, providing mothers in charge of household food spending with the knowledge, skills-set, motivation, and self-efficacy of healthful eating can be influential in preventing the double burden of malnutrition. An intervention study targeting low-income, overweight and obese mothers to improve food choices, fat-consumption habits, and physical activity in their 1- to 3-year-old children, has shown promise .In this literature review we aimed to describe correlates of the double burden of malnutrition using the socio-ecological model. Correlates are factors associated with the double burden of malnutrition, but not necessarily determinants that imply causation . The majBecause the double burden of malnutrition is a complex phenomenon, the socio-ecological model was successful in depicting the relationships among the correlates of the double burden of malnutrition across multiple levels. Currently, the evidence regarding correlates of the double burden of malnutrition is dominated by research at the individual and interpersonal levels. Much of the evidence for organizational, community, and policy levels is based on studies pertaining to overweight and obesity. Hence, some have argued that statistically, double burden of malnutrition such as SCOWT pairs are not independent from the components of maternal overweight status and childhood stunting but depend heavily on the prevalence of overweight mothers . Others Even though some have suggested that the double burden of malnutrition in the form of stunted child and overweight mother pairs (SCOWT) is merely a statistical artifact , the heaThis narrative review is intended to describe correlates of the double burden of malnutrition in the context of the socio-ecological model. Once there is sufficient evidence to describe correlates on all levels of the SEM through a systematic review or meta-analysis, a more objective picture of the double burden of malnutrition will emerge. Limitations for this narrative review include the restriction of article inclusion in the English language and dependence on the coverage of the PubMed database. Some relevant studies and grey literature might not be captured using this search strategy, and that could affect the current narrative. Although evidence was limited for the double burden of malnutrition at the organizational, community, and policy levels of the SEM, this review explained the impact of those levels adequately using correlates of overweight status and obesity. Considering that overweight status and obesity are part of the puzzle in the double burden of malnutrition, we do not expect the effect of the correlates to be very different. We realize that by understanding the double burden of malnutrition through the socio-ecological model, our efforts to tackle the double burden of malnutrition cannot be spatial. Furthermore, we offer some potential intervention strategies based on the SEM that might be useful for future interventions.The double burden of malnutrition is a public health phenomenon associated with an array of socio-ecological determinants. Implementation of an integrative model such as the SEM offers a potential solution for combating the complex problem of the double burden of malnutrition. Correlates at each level should be addressed holistically and efforts can target individuals, households, organizations, communities, and governments. Addressing malnutrition in all its forms requires an integrated approach to address the root causes of malnutrition at all stages of human development.


Recent transformative changes in science education require new learning opportunities for teachers—opportunities that include rich images of classroom enactment of the reform vision. One fruitful way for doing that is to use video clips of instruction.Teachers do not, however, learn how to improve their instructional practice from simply watching and reflecting on classroom videos. The videos need to be carefully selected and embedded in professional development in ways that—through facilitator-led, participant-centered discussion—can help teachers to notice and reason about important aspects of instruction and learning that occur in the video. Consistent with the recent efforts to identify planning and facilitation approaches that guide effective professional development (PD) programs, in this paper, we adapted the Five Practices Framework for orchestrating productive classroom discussions to describe how PD facilitators plan for and enact professional learning tasks to help science teachers learn within a video-based PD program. These practices include anticipating, sequencing, monitoring, selecting, connecting and two additional practices that set the stage for the five practices .Our analyses of the video-based discussions in the PD provide insights into how the facilitators engaged teachers in video-based conversations by using the practices of monitoring, selecting, and connecting. The monitoring moves, such as clarifying, countering, and redirecting, were used by the facilitator in nearly all the PD sessions. Similarly, selecting moves were used and were consistent with the goals of the PD. Finally, analysis of facilitators’ and participants’ connecting comments indicated their increased capacity to make connections to the bigger ideas of teaching science by maintaining the cognitive demand on students’ thinking.This paper provides elaborated descriptions of the five practices for planning and facilitating video-based PD and the ways in which they were enacted in a video-based PD program in science. In so doing, it proposes five practices as a guiding framework to support teachers’ learning from videos. Overall, the study’s results endorse the promise of a goal-driven, theory-informed design that foregrounds careful attention to teachers’ thinking in ways that support their understanding of complex classroom interactions.The online version of this article (doi:10.1186/s40594-017-0086-z) contains supplementary material, which is available to authorized users. The Framework for K-12 Science Education NRC,  and the As with other transformative reforms, teachers will need access to carefully designed professional development (PD) Wilson,  to help videos focus teachers’ learning on real classrooms and capture teaching in all of its complexity while, at the same time, affording space and time for reflection  on which we focus as we describe and use the Five Practices Framework. Although the Five Practices Framework provides us a lens to examine the design and enactment of any video-based PD program, here, we illustrate its use—in very concrete and tangible ways—with a particular PD program, TSCD. In the following sections, we unpack each practice, first by conceptually describing it, then by elaborating the role that it played in the design and enactment of the TSCD-PD. The second section introduces practices that are related to The framework, first used at the classroom level in mathematics  analysis of science instructional tasks as presented in written materials and 2) discussion of a video case that illustrated the classroom enactment of a high-level task, most typically one of the tasks from the Design Unit that was just analyzed. discussiPrevious studies of TSCD-PD have found positive impacts on teachers’ learning to notice as well as impacts on their instructional practices. More specifically, analysis of interviews before and after TSCD-PD, during which teachers were asked to respond to novel video clips presenting the enactment of cognitively demanding biology tasks, indicated an increase in teachers’ tendency to notice important features of classroom interactions. Teachers began to see teaching as constituted in the interaction of the teacher, students, and task (as opposed to a view of teaching as a solo act) . The design of TSCD-PD is also grounded in a view of learning that takes into account the contexts within which people interact as well as their access to resources such as ambitious curriculum materials Greeno, . This pecognitive demand, which is defined as the level of thinking required of students to complete a particular activity  at a high level of cognitive demand. This was followed by a video in which that same task—same classroom, same lesson—was enacted. In this case, when students actually went about working on the task, their thinking was very shallow and focused on the scientific terminology at a superficial level. In the third TSCD-PD session, participants, once again, analyzed a video showing a high-level set up, but of a different science task. Then, they viewed and discussed two different video clips, both of which represented high-level student thinking as students worked on this cognitively demanding task in the same classroom.The design of the PD tasks in the fourth and fifth TSCD-PD sessions was again guided by research; this time, it was undergirded by a line of research on learning from contrasting cases , such as the nature of teacher questioning. All of these factors were listed on the chart paper; in other words, they were during the PD sessions. In what follows, we will provide a detailed description of these three facilitation practices. Moreover, we will also provide an analysis of the actual video-based discussions that unfolded over the TSCD-PD sessions in which videos were used. It will provide insights into how the facilitators engaged teachers in the video-based conversations by using the practices of monitoring, selecting, and connecting.While the first two practices  of the Five Practices Framework occur during the planning phase for video-based PD, the remaining three practices  are related to facilitating productive video-based discussions For our empirical analysis, we used transcripts of video records of six TSCD-PD sessions. Each session was about 3 h, approximately 2 h of which consisted of discussion around the videos. The first author was the facilitator of all the PD sessions. The second author mostly played a participant observer role and occasionally supported the facilitation of the sessions by interjecting comments or questions into the discussions. Thus, her comments were also coded as “facilitator moves” in our analysis. A mathematics teacher and two other researchers, who were part of the larger project, also attended some of the sessions and from time to time made comments. These two researchers’ comments were not coded as facilitator moves.monitoring and selecting practices. More specifically, we grouped van Es’s codes of clarifying, countering, redirecting, linking participant ideas, distributing participation, and validating participant ideas under monitoring and highlighting, lifting up, and pressing under selecting  whether the facilitator and/or the participant(s) made the connection and (2) whether the participants’ connecting comments were best characterized as (a) surfacing more clear reasons/factors associated with maintenance or decline in cognitive demand by comparing and contrasting two video clips or (b) labeling by giving the factor a name that they generated and adding them to the list of factors associated with maintenance and decline, or trying to use the labels that they had added to the list of factors.None of the facilitator moves identified in the van Es framework was tightly related to the Five Practices Framework  how the class as a whole is doing and (b) which pieces of student work might be worth selecting for sharing with the whole class. We define To examine the extent to which monitoring actually happened in the TSCD-PD, we analyzed each facilitator move in the transcripts of the TSCD-PD sessions. As shown in Table clarifying which involved restating and revoicing to ensure common understanding of an idea. Also noticeable was the increase in validating participants’ ideas in the last two PD sessions. We suspect that this increase was spurred by that fact that participants were analyzing their own and each other’s video clips in these last two sessions and therefore might have needed more facilitator validation in order to feel comfortable sharing their ideas about their colleagues’ videos. van Es et al.  by selecting certain participant contributions to highlight and particular pieces of video clips to draw participants’ attention to. Just as a teacher selects student work by its potential to bring out important ideas related (or “on the way”) to the learning goal, the PD facilitator can elevate certain things and not others as a way of scaffolding the learning of the group as a whole toward the identified goals for teachers’ learning.Selecting pieces of student work to highlight is a critical practice for classroom teachers. If selected well, the pieces of student work will provide fodder for classroom discussion that moves the class as a whole toward the learning goal of the lesson. “Selecting,” done well, allows the teacher to both build on student thinking and lead learners to the canonical understanding that she wants them to leave the lesson with. Similarly, in PD, the To examine the extent to which this practice was actually adopted by the TSCD-PD facilitators, we examined the facilitator moves that were coded as highlighting, lifting up, or pressing under the van Es framework. These moves allow facilitators to choose certain ideas to discuss with the participants. Unlike classrooms in which actual  pieces of student work are available for selection, TSCD-PD sessions did not produce physical pieces of participants’ work. Instead, we consider participants’ comments (as the tangible products of their thought processes) as the “items” that are available for “selection.” For example, the facilitator can choose to focus on particular comments that the participants make while gently disregarding others. Similarly, the facilitator can purposefully choose to bring participants’ attention to certain ideas illustrated in the video clip.Like with the monitoring moves, our analysis provided evidence that selecting moves were used in nearly all the TSCD-PD sessions, but in comparion to monitoring moves, there were relatively lower frequency of selecting moves  questioning; I just want to go back to this heated debate part. So I think it starts—let’s start from line 70…As shown in Fig. As illustrated in this excerpt, the facilitator invited participants to focus not only on what students were saying but also on what the teacher did in relation to what students were saying .Linda: Oh. She probably increased the cognitive demand.Susan: There’s no guidance whatsoever.John: Right.Barbara: I said, the teacher did not give much direction, was my first comment.PD participants were asked to first write their reactions during private think time before the discussion began.Carol: Well, she guided them. She just didn’t guide them through the worksheet.Facilitator: So first, Ms. [Linda] Williams, say more about what you mean, that she increased the cognitive demand.As expected, facilitators also elevated participants’ ideas about cognitive demand. For example, in session 3, participants were discussing whether the cognitive demand of the task was maintained during its implementation, which was shown in the video:pressed participants to say more about their ideas related to cognitive demand throughout the PD sessions. Pressing is used to “prompt participants to explain their reasoning and/or elaborate on their ideas” . The following excerpt illustrates how the facilitator prompted participants to say more about their categorization of the level and kind of student thinking in the video based on the categories of the TAGS:Carol: I said low/high. I gave the first one a 2 [cognitive demand of tasks involving scripts]Facilitator: Which 2?In the above example, the facilitator took up Ms. William’s comment about cognitive demand and made it the object of the discussion by asking Ms. William to expand on what she said. Facilitators also Carol said she categorized the level and kind of student thinking in the video into level 2 based on the TAGS. However, level 2 of the TAGS consists of three categories depending on whether or not students are positioned to engage in scientific practices. Thus, to invite participants to think about the cognitive demand level in more detail, the facilitator asked Carol which level 2 category of the TAGS she was referring to.Nancy: I thought Ms. [Linda] Williams asked them nice questions.Facilitator: Yeah, yeah. This is why I want to look at her questions, because –Nancy: Well, I wrote them all down.Facilitator: —if you can—I mean, in this classroom, I think we’re all in agreement that it was all about like “Why?” “What does it mean?” “Tell me what two bands mean.”Carol: Literally, she just kept saying, “What does it mean?”Facilitator: But something was not working. I just want to talk about it. So she was like pushing them and—Nancy: Well, I wrote she pushed them in a few different spots with their own line of thinking.Facilitator: So let’s look at some of the questions that she was asking ____ –As shown in Fig. In this classroom video excerpt, Ms. William was repeatedly asking the same questions instead of tailoring her questions to how individual students were thinking. After hearing Nancy’s comment on Ms. William’s questioning, the facilitator invited participants to think harder about her questions, specifically in relation to what students were saying and how they were thinking about the task. In short, the facilitator lifted up Nancy’s comments on Ms. William’s questions and invited participants to analyze Ms. William’s questions in more detail because there was something to learn there about the factor related to questioning.All in all, our detailed coding of the facilitators’ highlighting, lifting up, and pressing moves indicates that facilitators were selecting ideas for further discussion to advance participants’ understanding toward the goals of the TSCD-PD. Specifically, facilitators tried to focus attention on participant comments about teaching-in-interaction with the students and the task, making sense of the cognitive demand in the classroom videos and identifying factors associated with maintenance and decline. Pressing for student thinking was also prevalent across the PD sessions, which is not surprising given that participants made decisions about the level and kind of student thinking by closely making sense of students’ ideas. Therefore, in addition to focusing on teaching-in-interaction, participants,not surprisingly, needed to discuss students’ sensemaking. This finding is consistent with the recent studies, which emphasize supporting teachers’ learning to make sense of students’ thinking  had just took the observation. That’s how I handled it (referring to when she taught the same lesson), so (tell the students) “just look and Carol: Oh, no, I had them do both [observations and interpretations of the data].Susan: Both at the same time?Carol: Yeah.Susan: Okay.Researcher: Which I think worked better. At least at that level.Linda: Well, they all seemed to want to start with a rule, and then explain it.Carol: I pretty much just told them, whatever you tell me, you have to be able to prove it.Linda: Right.Carol: So with that, they had to do both (they had to make observations of the data and interpret those observations).Facilitator: So can we add this to our list of maintenance factors? Asking for evidence for students’ claims or arguments or explanations? Do you think that it helped to maintain cognitive demand?Linda: I—well, I said—I said always keep them engaged in the scientific practice. Is that the same thought (the same factor)? Like to maintain a lesson, you have to keep them focused on the practices as well?Figure As illustrated in this excerpt, participants were discussing an instructional practice that Carol had adopted—requesting that students provide evidence for their claims—which they thought was influential in students’ making sense of the data. The facilitator suggested adding this instructional practice to the list of factors that they were generating on chart paper. Then, the discussion continued with Linda’s comment about whether one of the existing factors in the list  already included this idea of asking students for evidence for their claims. So, they were negotiating what factor to add to the list and how to best represent it.sensing teaching factors that might be playing an important role in what and how students were thinking, to surfacing specific instances of teaching practices that impacted student thinking, and to labeling them and trying to use the labeled factors in their analysis of their own videos.Our analysis also revealed a change over time in participants’ comments related to the factors of maintenance and decline across the TSCD-PD sessions. The nature of their comments differed qualitatively from session to session, following the trajectory of sense instructional factors associated with maintenance and decline. For example, in session 2, one of the PD participants said:Participant: Yeah, that’s what I wrote. Her (the teacher in the video) questions are all statements. She did everything so they technically could just sit back and chill.Facilitator: Ah, okay, so you are saying that students can just sit back and then not do anything—ah, she could—.Participant: Because of how she presented it, she didn’t put anything—she did all the work. She didn’t put anything on them.In sessions 2 and 3, participants began to “sense” that teachers could shape the level of student thinking. Their comments were unsophisticated involving general—even vague—terms. Remember, the participants have not yet been introduced to the idea that the cognitive demand of high-level tasks could be maintained or declined or to the instructional factors. That is why these comments were not coded as “connection to factors.” Nevertheless, we were able to identify comments which reflected the participants’ beginning to As this excerpt illustrates, the PD participant recognized how the questions/statements that the teacher in the video asked influenced the students’ thought processes. She described that the teacher did all the thinking work for the students. Similarly, in session 3, Carol said, “So like if you ask them the question and almost give them the answer, you can take the thinking away from the kids and think for them. That’s sort of what she (the teacher in the video) was doing.” Again, Carol explained, using her own words, how the teacher in the video lowered the demand on students’ thinking and reasoning.The nature of participants’ comments related to factors began to change in session 4. This was not surprising because, as we discussed earlier, in the beginning of session 4, participants were introduced to the idea that cognitive demand can decline during the implementation of a high-level task. After this, participants began viewing the videos through this new lens.surface specific instructional factors with an explicit reference to the idea of why cognitive demand might have been maintained or declined. In this session, one video illustrated a high-level task that was proceduralized by the teacher; in the second video (which featured the implementation of the same high-level task), the teacher focused on helping students understand the underlying biological idea behind the modeling task about genetics. Recognizing the differences, Linda said:…I have two thoughts right now, that the first teacher (in the video) kind of turned this totally into a Punnett square because there were a couple examples of this. The very first group did fertilization and didn’t have alleles in their egg and sperm. She (the teacher) didn’t make them pull them apart. She made them add the alleles.… it went against that biological concept of the alleles don’t come after or don’t combine. So she didn’t do the meiosis part. Second piece of evidence was once she started doing “this” and “these” with all those groups, she just kept saying, “How many combinations did you get? How many combinations did you get? How many combinations did you get?” Or, “How many combinations can you get?” And they were like, “Oh, let’s do it. Okay, hurry up.” And I even saw that one kid go, “Come on, let’s roll with it,” and he just started sticking stuff and they started combining. It was all about the combinations for her, how many combinations—In particular, while analyzing the contrasting video cases in session 4, their “connecting comments” began to Only because I felt like the teacher was doing all of the cognitive work, and just kind of pulling like words, instead of really saying, well, “What are you trying to tell me? What do you mean by that?” They were asking questions, she was answering it. It was that back and forth. And then in the second video I said it was a high level, and level 4, only because I think the small group work really helped. I think if it was just the classwork, maybe she wouldn’t have been able to do that. I think adding that small group work really brought it up, because then students were actually looking at data, analyzing data, making observations, comparing data between different results from different crosses. They were struggling with the information, so I thought there was a high cognitive demand, because, you know, they were really trying—all of them really started to notice, well, all of these PCRs and all of these western blots are the same. Why don’t they all look the same? So they’re really struggling, trying to figure that out. So I thought that that made it high level. And the teacher wasn’t just answering the questions.As illustrated in this excerpt, Linda surfaced how proceduralizing the task and focusing on the end result could influence the level and kind of student thinking. Similarly, in session 5, participants continued to surface instructional factors associated with maintaining or declining cognitive demand without naming them factors. For example, when contrasting the two videos, Barbara said:During her discussion of the contrast between the videos, Barbara was surfacing factors that could play a role in determining the level and kind of student thinking that occurs in response to a task. For example, she uncovered that in one video, the teacher was directly answering the questions that students asked, instead of asking follow-up questions to elicit students’ thinking. The nature of the intellectual work that the students engaged in was, then, different in these two classrooms.own classrooms. In the beginning of session 6, the facilitator engaged participants in a “summary activity” during which she introduced the idea of factors to the participants as they were summarizing what they had done in the prior sessions with the contrasting video cases. Then, the facilitator said:So when we talked about the differences, we actually talked about the factors that cause maintenance or decline of the task, actually. But we did not call them factors, but you started to call them factors about what causes maintenance or decline. So, let’s call them factors associated with maintenance or decline…Finally, in the last two sessions, participants analyzed videos from their Susan: I think the method of questioning, if that makes sense.Facilitator: So say moreSusan: If I were going to do that task where you give them the flowers, which is what that video was, right? So one way to get them to realize the different offspring would be like, okay, so let’s look at the first one. It’s red and it’s white. What do you notice about the offspring? They’d be like, oh, it’s red. Okay. How is that different than all the rest? That would be a decline, because you’re really direct—like this is point blank the easy answer.During this summary activity, participants began to list factors associated with maintenance and decline, factors that were brought up (mostly) during the discussion of the contrasting video cases. Initially, the participants shared things like classroom management, student absenteeism, and class and/or group size as factors associated with the decline in cognitive demand. The facilitator added these factors to the list but then gently invited them to think about factors that are more under their control. The discussion then started to move toward developing a list of instructional factors, such as asking open-ended questions and eliciting student thinking. For example, Susan suggested that teacher-questioning was a factor associated with maintenance and decline. She said:I think that you were asking questions for them to clarify, and allowing them to work through the problem. So that one heated-debate group, you allowed them to work through it. And then also that the students were developing the rules on their own. Like even you say, so you’re saying, and then you go into a repeat back of what they’re saying to clarify. What does that mean on here? So you’re kind of like pushing them to explain it. And then even like (line) 137, the student says, now you just match them up, and you say, what? What are you matching? And you’re pushing them to like clarify it that way.After generating this list of factors, the participants started to discuss the video clips from their own classrooms. During their discussions, they often referred to the instructional factors listed on the chart board and they sometimes added new ones to the list. For example, the following excerpt illustrates Susan’s attempt to use the factors of maintenance as they were analyzing Nancy’s video in session 6:As illustrated in this excerpt, Susan was sharing her observation of the video by connecting teacher’s action’s to a broader instructional factor associated with the maintenance of cognitive demand. One of the maintenance factors listed on the chart paper was “Questions: Clarification questions, open-ended, making thinking visible for students.” Susan was clearly trying to use this language to explain how the teacher was making students “work through” the task by asking clarification questions.All in all, our analysis of facilitators’ and participants’ connecting comments suggested that TSCD video-based PD fostered participants’ capacity to make connections to the bigger ideas of teaching science by maintaining the cognitive demand on students’ thinking.The new vision for the next generation of science teaching and learning will require increased capacity on the part of teachers. One of their biggest challenges will be to learn to enact new, high-demand tasks in ways that engage students with the scientific concepts while, at the same time, engaging them in the science practices. As with other transformative reforms, science teachers will need to participate in carefully designed professional development to help them learn how to successfully support their students’ learning using complex tasks.Professional development that is centered around viewing and discussing classroom videos is an increasingly recommended approach for supporting teachers’ capacity to enact the vision of NGSS. Like any professional development, however, video-based PD is not self-enacting. It will succeed or fail based on how PD providers plan for and facilitate experiences that are built around videos.Despite being called “a new cadre of prominent players on the educational scene” , the broad-based alignment between preparing for and enacting a successful lesson and designing and facilitating a PD session (both are teaching and learning situations around complex tasks) allowed us to make necessary adaptations fairly easily. In short, we found that using the framework to guide our inquiry was possible. But what has it enabled us to see that otherwise we may not have and what, if anything, has it obscured?The practice of setting goals turned out to be a surprisingly powerful lens through which to view the design and enactment of video-based PD. The initial detailed specification of goals for the TSCD-PD provided a host of benefits downstream. For the facilitators, the goals and subgoals provided guidance for the design of each session. For the researchers, the goals and subgoals became a way to monitor if discussions were moving in a productive direction or if they had become a “free for all.”combined use of goals and the “selecting practice” during the actual discussions. Using both to interpret facilitator moves revealed facilitator choices—made mid-stream during discussions—that otherwise would have remained invisible. By illuminating not only the fact that the facilitator “pressed” or “lifted up” certain participant comments but also coded what the essence of those comments were, we witnessed deliberate choices on the part of the facilitator to pay attention to teachers’ thinking and to move their thinking toward the goals/subgoals of TSCD-PD (and not to pursue other topics). Attending to teachers’ thinking is consistent with other researchers’ recognition of the need for facilitators to learn how to notice teacher thinking  did not (indeed we could not) “label” the three phases of sensing, surfacing, and labeling until we began to reflect on the experiences and the data. It was only then that we realized how the sessions combined elements of participants’ grappling to make sense of videos with solidifying their understandings. Treating teacher learning as a progression has recently been emphasized by others as well. Jackson et al.  examinedsequenced: Grappling with challenging ideas, followed by a consolidation that builds on the emerging understandings rather than being espoused or proclaimed from the start. The way the sequencing practices were adopted by the TSCD-PD designers/facilitators provides a concrete illustration of how teachers’ learning experiences can be sequenced within the PD sessions and more importantly across the PD sessions by approaching teacher learning as a progression.We think that the sensing, surfacing, and labeling pathway can be used by others to both design PD and to evaluate teachers’ learning progressions in PD experiences. It would be especially useful to apply to the study of how participants might grow and develop over the course of an extended, multi-session professional development experience. The design allowed for large stretches of participant-generated understandings gained through grappling with complex features in the video clips. However, there were also times for “telling,” as when the facilitator expounded on the “journey of a task” or factors associated with maintenance and decline. Both forms of learning can be valuable, but especially when they occur in the order in which they were and execute a sequence of PD sessions around the medium of video. Considered in tandem with previous studies on TSCD-PD, we also see our findings as endorsing the promise of goal-driven, theory-informed design that forefronts careful attention to teachers’ thinking to support their understanding of complex classroom interactions and ambitious instructional practices. Future work will involve implementing TSCD-PD in additional sites with different facilitators Additional file 2:Categories for coding the substance of participant ideas selected by the TSCD-PD facilitators. (DOCX 111 kb)


Modelling fluid flow in an unsaturated porous medium is a complex problem with many practical applications. There is enough experimental and theoretical evidence that the standard continuum mechanics based modelling approach is unable to capture many important features of porous media flow. In this paper, a two-dimensional semi-continuum model is presented that combines ideas from continuum mechanics with invasion percolation models. The medium is divided into blocks of finite size that retain the nature of a porous medium. Each block is characterized by its porosity, permeability, and a retention curve. The saturation and pressure of the fluids are assumed to be uniform throughout each block. It is demonstrated that the resulting semi-continuum model is able to reproduce (1) gravity induced preferential flow with a spatially rich system of rivulets (fingers) characterized by saturation overshoot, (2) diffusion-like flow with a monotonic saturation profile, (3) the transition between the two. The model helps to explain the formation of the preferential pathways and their persistence and structure (the core and fringe of the fingers), the effect of the initial saturation of the matrix, and the saturation overshoot phenomenon. In oil recovery applications, two immiscible and incompressible fluids—water and oil—move in a complex space of pores in a reservoir rock. In vadose zone hydrology, the two fluids are water (incompressible and wetting) and air (compressible and non-wetting). Many other applications of porous media flow have appeared, such as carbon sequestration4, the transport of radionuclides in the soil5, filtration6, hydrogen storage7, geothermal engineering8, and applications in biological systems and biotechnology9. This paper concentrates on the flow of water through soil which is not fully saturated. The lack of understanding of vadose zone hydrology is one of the main bottlenecks in our understanding of the hydrological cycle10.The flow of liquids through porous media is a long standing, well-researched, and yet still not fully understood problem. There are two broad areas that draw heavily on understanding porous media flow—oil recoveryProblems concerning fluid flow are notoriously difficult because of the non-linearity caused by inertial forces . In the porous media setting, the flow velocity is usually so small that inertial forces can be neglected. Still, the problem is difficult because the pressure in the wetting fluid at each point is determined by the interplay between hydrostatic forces caused by gravity and capillary forces caused by the presence of the menisci of air–water interfaces, which are in turn determined by the geometry of the porous matrix. Since the geometry of the matrix is so complex that it cannot be fully resolved in any reasonable model, some simplification or approximation is needed.11. The mathematical tools of continuum mechanics  were standard and ready to be used for the description of porous media flow. Continuum mechanics uses the concept of the reference volume element to transition from naturally discontinuous pore-level quantities to continuous and differentiable macroscopic fields . Various forms of mass conservation equations for these fields are then derived in the form of partial differential equations, the most famous of which is the Richards’ equation (RE)12.Traditionally, porous media flow was modeled in the continuum mechanics framework3. The most notorious discrepancy between theory and observation has been what is called the finger flow regime, in which an initially dry porous medium is exposed to a uniform and constant influx of water at the upper boundary. This phenomenon has been studied extensively since the early 1970s14. While the RE predicts a stable waterfront that moves as a travelling wave downward through the porous matrix, experiments often show the evolution of a spatially rich system of rivulets (fingers) that conduct water downwards through preferential pathways, leaving a substantial part of the matrix almost dry19. The tips of the fingers are usually almost fully saturated while the tail leaves an under-saturated trace. This phenomenon is called the saturation overshoot. The fingers are stable in the sense that subsequent infiltration proceeds through these pre-wetted preferential paths15. It has been proved that the RE is fundamentally incompatible with finger flow because it does not admit saturation overshoot22. There is enough experimental evidence of the dependence of the finger velocity, width, and overshoot magnitude on the initial saturation and flux magnitude27. Several extensions of the RE have been proposed37; however, none is able to reproduce all these observed dependencies of the finger like regime2.Over the years, there has been a growing body of experimental evidence of observed unsaturated porous media flow regimes that were not easy to describe or explain by the standard continuum mechanics based approach39. In this framework, the porous matrix is modelled by a discrete grid of pores which are either empty or full, and the local discrete rules of pore filling and emptying are executed on such a grid. Various flavours of this approach have been introduced under the names of percolation, invasion percolation, modified invasion percolation, etc.45 Although some features of unsaturated porous media flow may be captured very well by these models , the discrete nature of the models makes it hard to recover the saturation overshoot behaviour. Moreover, discrete models usually do not capture time in a physically meaningful way. The local percolation rules usually get the order of the pore-filling (or draining) events right, however, the physical times of the events cannot be recovered. Zhao et al.46 reported an unprecedented comparison of 14 state-of-the-art pore-scale models to reproduce recent experimental observations of multiphase fluid flow in porous media.Since the 1970s, a different modelling approach has been evolving, which is based on percolation theory and cellular automata47 tried to combine the virtues of both the continuum and discrete models. The authors proposed an approach called Macro Modified Invasion Percolation in which the porous matrix is divided into macroscopic  blocks that retain the characteristics of a porous medium. Each block is fully characterized by its wetting pressure (i.e. the pressure needed for water to invade and percolate the block and make it conductive) and its draining pressure (i.e. the pressure needed for air to displace water from the block). The authors use the model successfully to simulate three different settings—finger flow49, the buoyancy-driven migration of gas in a water saturated sand column50, and water flow through a rough-walled fracture51.The seminal work of Glass et al.52 proposed a semi-continuum model (the term was coined by DiCarlo53), which treats space in a discrete manner but keeps time continuous. It was demonstrated that a one-dimensional version of this semi-continuum model is able to successfully reproduce qualitatively and quantitatively all the features of one dimensional saturation overshoot behaviour reported in the literature.Inspired by this success, Kmec et al.52. The model is again based only on well-established physics, measurable parameters, and material characteristics. We show that the model is able to reproduce both the finger-like regime  and the diffusion-like regime , and the transition between the two. In the finger-like regime, the model reproduces the persistence of the fingers and captures their spatial heterogeneity well. Further, the model helps to explain the inner structure of the finger—the mobile core and immobile fringe—that is observed in experiments. The well-known two-dimensional experiments of Glass et al.56 and Rezanezhad et al.57 are reproduced by the model. The proposed model is not a numerical scheme to solve the RE and does not reduce to the RE even in the limit of vanishing block size.In this paper, we present a two-dimensional version of the model which is a straightforward extension of the 1D case52 proposed a one-dimensional version of a semi-continuum model of unsaturated porous media flow. The purpose of the model in 1D was to replicate experiments in a narrow sand-filled tube while keeping the model as simple as possible. Here we extend the model to two spatial dimensions because in 2D there are many more features of the finger flow that can be tested. A 2D model aims to capture experiments in a vertical Hele-Shaw cell filled with sand used for experiments e.g. by DiCarlo25. The distance between the two parallel plates is small and thus the dependence of the quantities of interest on this coordinate can be neglected; hence the notion of 2D porous media flow.Kmec et al.The porous medium is modelled as a regular rectangular grid of see the “” sectioni, j]. The model simulates the motion of the wetting fluid inside the 2D porous medium by tracking the following three quantities:t. Saturation is assumed to be uniform throughout each block but varying continuously in time;the saturation t. Pressure is assumed to be uniform throughout each block but varying continuously in time;the pressure t. The fluxes are assumed to be continuous in time.the fluxes The evolution of these three quantities is modeled by the following three rules.Each block is denoted by its row and column indices  denotes the pressure in the wetting fluid given by the retention curve. The function k(S) [-] stands for the relative permeability, i.e. the ratio of the effective permeability at a particular saturation to the intrinsic permeability. The relative permeability is usually modelled by a power law. Here we adopt the form derived in65:m corresponding to the main wetting branch. Let us denote the effective permeability of the porous medium Once the pressure in each block is updated, new values of the fluxes among the blocks are calculated. The flux is modeled by the standard Darcy-Buckingham lawentclass1pt{minimaThe flux update is the only step where we slightly depart from the standard implementation of the Darcy-Buckingham law. We proposed the following discrete implementation66, where the authors show that the geometric mean is appropriate by means of numerical experiments in random pore networks.Thus, the lateral fluxes , and the dependence of the fingers on the initial saturation. Unless otherwise stated, the parameters used for the simulations are given in Table dx was inspired by the Macro Modified Invasion Percolation model developed by Glass et al.50.In this section, we demonstrate the capability of the model to reproduce the experiments by Glass et al.33; moreover, the authors introduce a perturbation directly into the wetting front at the beginning of the simulation.The porous medium is assumed to be homogeneous, i.e. there are no preferential pathways “hard-wired” into the porous matrix structure. This, however, does not mean that it is sensible to assume that the characteristics of all the blocks are the same. Such a model would resemble an artificial medium (e.g. uniformly packed glass beads) rather than a realistic porous matrix. Thus, we introduce a narrow and spatially correlated distribution of the intrinsic permeability of the blocks. This is the only parameter that is assumed to have a distribution; otherwise the blocks are identical. The distribution satisfies mentclass2pt{minim68, and thus we set 32 or Gomez et al.33, who initiate fingers by a perturbation of the wetting front at the beginning of the simulation. The fingers are fully developed after approximately 10 minutes and then they proceed downward until they reach the bottom boundary. The saturation in the fingers exhibits the typical overshoot pattern—the bottom part of the finger is close to full saturation while the finger tail is much drier. The length of the oversaturated zone is approximately 17 cm, which matches well with the experiments15. One may observe the long persistence of the fingers (12 hours of flow is simulated), which was experimentally observed e.g. in57. Moreover, Glass et al.55 and DiCarlo et al.18 reported that after hours or days of steady infiltration, the chamber was fully wet; however, most of the flow was confined to the original finger cores and the saturation was much lower around the fingers. This is exactly what can be seen in the last snapshot in Fig. First, we wish to demonstrate the instability of the wetting front—the formation of macroscopic fingers—and their persistence in time. In experiments, this fingering regime is observed for low initial saturation of the matrixentclass1pt{minimaentclass1pt{minima54 and Rezanezhad et al.57. Using a dye tracer, the authors showed that the flow is dominant in the centre of the fingers (the finger core) and water stagnates at the periphery (the finger fringe). Therefore, each finger is separated into a mobile core and an immobile fringe. Figure The persistence of fingers was explained e.g. by Glass et al.57. Figure 57 where the authors claim that the pressure at 55.Understanding the stability of such a flow structure is crucial and it can be explained by tracking the pressure-saturation states of the blocks on the retention curve during the passage of the fingersee Fig. , point \58, we modified the wetting branch by means of a cubic spline. The left panel of Fig. We suggest that the model presented here may help to explain the lateral expansion of the fingers. In the previous paragraph, we explained that our choice of the retention curve led to fingers that do not expand laterally. However, a modification of the retention curve shape allows for lateral expansion. Let us assume a retention curve with a larger gradient in the left part (i.e. steeper dependence of pressure on saturation in a dry medium). Since it is difficult to obtain such a retention curve by the van Genuchten model57 and explains the slow lateral expansion of the fingers in Supplementary Video 2.Let us repeat the simulation shown in Fig. lity Eq. . Here, w69. Most interestingly, as the initial saturation increases from dry to fully saturated, the flow pattern changes qualitatively from the fingering regime  to a diffusion-like wave water front travelling uniformly (without any overshoot). Moreover, the transition from the fingering regime to the diffusion regime is not monotonic. With increasing initial saturation, the fingers first become faster and narrower, but then they become slower and wider again before disappearing completely into the diffusion-like regime. The model presented here correctly captures both the qualitative and quantitative aspects of this wonderful transition. We again wish to stress that the model does not introduce any artificial or non-measurable parameters to do so.Let us now examine the effect of the initial saturation Figure 57 provide us with an opportunity to test the model in the situation when a layered porous medium is subject to a constant influx of water across the top boundary. Rezanezhad et al.57 use a Hele-Shaw cell  has smaller grains on average, and therefore its retention curve should be steeper compared to the homogeneous layers. The saturated hydraulic conductivity of the heterogeneous layer was approximately three times lower than that of the homogeneous layers. For details, see Rezanezhad et al.In the experiment, the top entclass1pt{minima57 showed that stronger capillary forces in the heterogeneous layer  were sufficient to disturb the finger flow. However, the fingering pattern re-appeared immediately in the bottom layer . We reproduce this behaviour in Fig. 57. If we introduced stronger horizontal spatial correlation of the intrinsic permeability in the middle layer , the flow pattern would be disturbed even more. Here, we only wanted to show that this effect can be reproduced by a small change in the retention curve.Rezanezhad et al.49 are moderately successful in reproducing the finger-like regime; however, the diffusion-like behaviour is beyond their capacity because there is no way to recover continuous saturation levels and physically meaningful time. At the other end, the Richards’ equation is known to reproduce the diffusion-like behaviour but the fingering regime is beyond its power as a result of impossibility of its producing the saturation overshoot22. Other models capture some features of the flow in the diffusion like regime or in the fingering regime, but there is usually a price—new parameters that are impossible to measure35, and/or artificial boundary conditions70 and/or disagreement with the experiments in other flow regimes except for the one that the model was tuned to71. The model presented here captures both the qualitative and quantitative aspects of unsaturated porous media flow both in the fingering regime and in the diffusion regime.The difficulty of modelling unsaturated porous media flow can be best understood by studying the effect of the initial saturation of the matrix on the flow pattern. As the initial saturation increases, the flow pattern changes qualitatively from the fingering regime to a diffusion-like regime. During this transition, the saturation overshoot gradually disappears and the finger width depends non-monotonically on the initial saturation (see the Results section). Macro Modified Invasion Percolation modelsdx. If we let To support this rather bold claim, it is crucial to understand the role of the block size It is well known that forward time discretization see Eq.  may caus57, which is well reproduced by the semi-continuum model. A close look at the simulations reveals two different scenarios of finger conjunction: the fingers either merge  or they converge and flow side by side without merging. In the first case, the saturation at the finger tip is high enough to break through the immobile fringes. Fingers also merge if the hydraulic conductance below the finger tip is low enough to force lateral expansion of the finger. On the other hand, sometimes two fingers converge without merging. This happened e.g. to the second and the third fingers from the left in Fig. Experiments show that fingers can merge or bifurcate57). Thus, by decreasing the length of the scanning curves (i.e. decreasing the “gap” between the two main branches), the length of the over-saturation zone of the finger also decreases. This is consistent with our simulations, see Supplementary Fig. The hysteresis of the retention curve plays an important role in the finger profile build-up. It is known that all points where saturation overshoot occurs are located on a scanning curve  and its characteristics, especially the saturation overshoot phenomenon. Invasion percolation models and their modifications, on the other hand, capture some features of finger flow but usually describe saturation as a binary variable thus missing a large part of the physical reality. The proposed model describes pressure and saturation as fields that are continuous in time but piecewise constant in space. This compromise between continuous and discrete modelling is able to reproduce (1) gravity-induced preferential flow with a spatially rich system of rivulets (fingers) characterized by saturation overshoot, (2) diffusion-like flow with a monotonic saturation profile, (3) the transition between the two. The model helps to explain the formation of the preferential pathways, their persistence and structure (the core and fringe of the fingers), the effect of the initial saturation of the matrix, and the saturation overshoot phenomenon. There remains an open question of the limit of the model as Supplementary Information.Supplementary Video 1.Supplementary Video 2.Supplementary Video 3.Supplementary Video 4.Supplementary Video 5.Supplementary Video 6.Supplementary Video 7.Supplementary Video 8.Supplementary Video 9.Supplementary Video 10.


During the COVID-19 pandemic, growth in citizen engagement with social media platforms has enabled public health departments to accelerate and improve health information dissemination, developing transparency and trust between governments and citizens. In light of these benefits, it is imperative to learn the antecedents and underlying mechanisms for this to maintain and enhance engagement.The aim of this study is to determine the factors and influencing mechanisms related to citizen engagement with the TikTok account of the National Health Commission of China during the COVID-19 pandemic.Using a web crawler, 355 short videos were collected from the Healthy China account on TikTok (with more than 3 million followers throughout China), covering the period from January 21, 2020, to April 25, 2020. The title and video length, as well as the number of likes, shares, and comments were collected for each video. After classifying them using content analysis, a series of negative binomial regression analyses were completed.P<.001) and comments . Title length was positively related to the number of shares , likes , and comments . Dialogic loop negatively predicted the number of shares . In comparison to appreciative information, information about the government’s handling of the situation  and guidelines information  were positively correlated with the number of shares, while the latest news was negatively related to the number of likes received . More importantly, the relationship between predictors and citizen engagement was moderated by the emotional valence of video titles. Longer videos with positive titles received a higher number of likes  and comments . Furthermore, for short videos related to government handling of the pandemic  and guidance for stakeholders , positive titles received a greater number of shares. Videos related to the latest news  received more likes if the video title displayed higher levels of positive emotion.Among the 355 videos, 154 (43.4%) related to guidance for clinicians, patients, and ordinary citizens, followed by information concerning the government’s handling of the pandemic , the latest news about COVID-19 , and appreciation toward frontline emergency services . Video length, titles, dialogic loop, and content type all influenced the level of citizen engagement. Specifically, video length was negatively associated with the number of likes (incidence rate ratio [IRR]=0.19, During the COVID-19 pandemic, videos were frequently published on government social media platforms. Video length, title, dialogic loop, and content type significantly influenced the level of citizen engagement. These relationships were moderated by the emotional valence of the video’s title. Our findings have implications for maintaining and enhancing citizen engagement via government social media. Citizen engagement on social media during times of public health crises, such as that experienced during the COVID-19 pandemic, provides governments with a valuable tool for communicating with and understanding the concerns and priorities of their citizens . With ciAlthough some studies have examined the relationship between government agencies’ use of social media and citizen engagement during public health crises, there are several obvious gaps that deserve further investigation. First, existing studies have paid extensive attention to more traditional social media, including Sina Weibo ,8, TwittThis study aims to address the above gaps by exploring the factors that drove citizen engagement through the TikTok account of the National Health Commission of China (NHCC) during the COVID-19 pandemic, in the context of China. Chinese governments, across different levels, have now started to realize the potential of TikTok for public participation, leveraging the platform for routine administration tasks. According to the latest report by the China Internet Network Information Center (CNNIC), the number of verified government TikTok accounts is 25,313, implying wide employment in the Chinese public sector . In thisBased on the characteristics of TikTok videos, our study built a moderated model that unraveled the moderating role of emotional valence among the differentiated effects of video length, title length, dialogic loop, and content type on the three dimensions of citizen engagement, namely the number of shares, likes, and comments .Video length refers to the duration of a video. Although several studies have examined the length of popular videos, few have investigated the impact of video length on citizen engagement on TikTok. For example, Zhu et al  analyzedTherefore, hypothesis 1 is as follows: video length negatively affects the three dimensions of citizen engagement via the official TikTok account of the NHCC, as measured by the number of likes, shares, and comments.Title length refers to the total number of words summarizing the video’s content in the title of an uploaded video. During times of crisis, citizens are usually motived by utility, craving information that relieves anxiety and eases panic . Longer Therefore, hypothesis 2 is as follows: title length positively affects the three dimensions of citizen engagement via the official TikTok account of the NHCC, as measured by the number of likes, shares, and comments.Dialogic loop emphasizes the importance of providing an interactive feedback loop, facilitating mutual communication between organizations and citizens . OrganizTherefore, hypothesis 3 is as follows: dialogic loop positively affects the three dimensions of citizen engagement via the official TikTok account of the NHCC, as measured by the number of likes, shares, and comments.Extant studies into health communication have identified that different content types have varying effects on citizens’ social media engagement behaviors. According to the Use and Gratification Theory, the degree to which media content gratifies individuals’ differential needs directly influences their media selection and usage behavior . AnalyziTherefore, hypothesis 4 is as follows: content type has significant differential effects on the three dimensions of citizen engagement via the official TikTok account of the NHCC, as measured by the number of likes, shares, and comments.Emotional valence refers to the positive and negative feelings triggered during an individual’s consumption of information ,18. EmotTherefore, hypothesis 5 is as follows: emotional valence will moderate the effects of video length, title length, dialogic loop, and content type on the three dimensions of citizen engagement via the official TikTok account of the NHCC, as measured by the number of likes, shares, and comments.For this study, we collected data from the official TikTok account of the NHCC, “Healthy China.” The official account was created on May 4, 2018, to help more widely disseminate health-related information. By May 12, 2020, the account had posted 576 short videos, had 3 million followers, and had received more than 8 million likes. Since the outbreak of COVID-19 in December 2019, the NHCC has actively uploaded relevant short videos. We used a web crawler tool to capture all videos uploaded to the official account from January 21, 2020, to April 25, 2020. In total, 364 videos were obtained. After manual checking, 355 were found to be related to the COVID-19 crisis. In addition, data about the video’s length, title text, number of likes, number of shares, and number of comments were collected.Citizen engagement through the official TikTok account of the NHCC includes three dimensions: sharing, liking, and commenting behaviors . We captVideo length is the duration of the video. The length of all 355 videos was captured from the “Healthy China” account using a web crawler.Title length relates to the number of words included in a video’s title. This study first collected the complete texts of 355 video titles using web crawlers, and then automatically counted the number of words in each text using Microsoft Excel (Microsoft Corp).Dialogic loop is measured by two indicators: posing and answering questions . If a quContent type includes 4 categories, namely the following: the latest news about the COVID-19 crisis, the government’s handling of the pandemic, appreciation for frontline emergency services, and guidance for stakeholders ), while guidance and government handling information received the least  and comments  received. The IRR value shows that a one-unit increase in video length leads to a decrease in the number of likes and comments by a factor of 0.19 and 0.39, respectively. However, the relationship between video length and number of shares is not significant. Thus, hypothesis 1 was partially supported.P=.01), likes , and comments . A one-unit increase in title length can result in a 2325% increase in the number of shares, a 750% increase in the number of likes, and a 685% increase in the number of comments. Thus, hypothesis 2 was supported.Hypothesis 2 proposed that a longer video title increases the level of citizen engagement. According to P=.03). This means that dialogic loop decreases willingness to share by about 44%. In addition, Models 2 and 3 show that dialogic loop is not associated with the number of likes and comments received. Thus, hypothesis 3 was not supported.Hypothesis 3 proposed that videos with multiple dialogic features were more likely to attract citizen engagement. Model 1 in P<.001) and guidelines information  were positively correlated with the number of shares. The IRR values mean that, compared to appreciative information, handling information would result in a 416% increase in the number of shares, while guideline information would lead to a 631% increase. Videos about the latest news were found to be negatively related to the number of likes , which means that posts about the latest news would result in a 54% decrease in the number of likes received, compared to posts about appreciative information. Interestingly, the number of comments did not vary significantly across different types of video content. Thus, hypothesis 4 was partially supported.Hypothesis 4 proposed that the degree of citizen engagement was influenced by the content shown in the videos. Since content type is a categorical variable, we treated appreciative posts as the reference group. Model 1 in P=.04) and comments . As P=.04) and government handling  information, the more positive emotion a video’s title had, the higher the number of shares the video received, in comparison to appreciative news. Videos related to the latest news  received more likes when their titles had higher levels of positive emotion. Interestingly, the title’s emotional valence has a weak effect or no effect on the relationship between content and other types of engagement behavior. Overall, emotion plays a moderate role in the relationship between video length, content type, and citizen engagement, but patterns vary across different types of engagement.We investigated the conditional impacts of the predictors by entering emotional valence and interaction variables into the negative binomial regression model. As seen in This pioneering study is the first to attempt to reveal how to promote citizen engagement with official government TikTok accounts during the COVID-19 crisis. To reveal the specific mechanisms of engagement, we proposed a moderated model, which investigated the moderating role of emotional valence on the effects of video length, title length, dialogic loop, and content type on the three dimensions of citizen engagement with the official TikTok account of the NHCC.First, we found that shorter videos and videos with longer titles generate greater engagement in general. On the one hand, video length negatively and significantly influenced the number of likes and comments received. This conclusion confirms the findings of Zhu et al , who fouSecond, this study found that content related to the government’s handling and guidance for stakeholders promotes citizens’ reposting behavior, while information related to the latest news about the crisis reduces the number of likes received. This further expands on the conclusion of Chen et al , who fouInterestingly, this study discovered that higher levels of dialogic loop significantly reduce the number of shares received. This conflicts with existing studies that examine how dialogic loops affect citizen engagement ,25,37. IMost importantly, this study confirmed that emotional valence can moderate the impact of video length and content type on citizen engagement, although the moderating effects vary in the three dimensions of citizen engagement. For longer videos, the more negative emotion the video’s title displays, the lower the number of likes that the video would receive. This pattern is almost the same for the number of comments. This means that longer videos with positive titles receive higher numbers of likes and comments. For short videos related to the government’s handling of the pandemic and guidance for stakeholders, positive titles received more shares. Videos about the latest news received more likes if the title had a higher level of positive emotion. This demonstrates the important role of the emotional valence of video titles in promoting citizen engagement through government TikTok accounts. This can be explained by The Social Sharing of Emotion Theory (SSET), which was proposed by Rimé and colleagues in the 1990s. The SSET posits that emotion is a critical motivator for information sharing and social interaction. In our daily life, emotional events can happen anywhere and at any time, and those who experience emotional events are likely to talk about them and the feelings experienced . ThroughThis research makes the following contributions. First, we not only empirically examined how governments have used new video-based social media platforms for public engagement in the context of a public health crisis, but also built a model with emotional valence as a moderator to explain the underlying mechanism of how video length, title length, dialogic loop, and content type affects public engagement with government TikTok accounts. Second, we reveal that although shorter videos are likely to attract more likes and comments, for longer videos, the emotional valence of the title is of critical importance. For long videos, the more positive the title, the more likes and comments it receives, and vice versa. Third, our study found that emotional valence displayed in the title plays a critical role in the impact of content type on public engagement. For videos focused on guidance and the government’s handling of the crisis, the more positive the emotion displayed in the video title, the higher the number of shares it received. In addition, videos related to the latest news received more likes when the title had higher levels of positive emotion. Fourth, our study found that dialogic loop is likely to reduce certain types of public engagement.This study has several practical implications. First, TikTok has become an indispensable channel for government-citizen communication, and governments should actively embrace this new method of communication. Second, for government entities producing videos for TikTok, shorter video length is preferred. If the video length is relatively long, it is better to have a title with positive emotion rather than negative emotion. Third, after the public health crisis, governments are advised to publish more information about their handling of the crisis, provide further guidance for stakeholders, and upload videos with positive emotion in the title to facilitate delivery.This study has several limitations. First, we focused on the official TikTok account of the NHCC. Whether the results of this research are equally applicable to local health departments is worthy of investigation. Second, it is worth exploring if the conclusions are similar in Western countries. There are notable differences between TikTok and YouTube ; althougIt is evident that fostering engagement through video sharing on TikTok provides public health departments with the ability to promote citizen engagement and accelerate the dissemination of health information. Nonetheless, how to sustain this positive effect is still unclear. Through analysis of 355 COVID-19–related TikTok videos scraped from the official NHCC account, this study addresses this knowledge gap by considering emotional valence as a moderator that determines the effect that video length, title length, dialogic loop, and content type have on the three dimensions of citizen engagement. In general, shorter videos and longer video titles elicit greater citizen engagement. Citizens prefer to view content about the government’s handling of the pandemic and guidance for stakeholders, and actively repost these TikTok videos. We confirmed the important role of emotional valence as a moderator and discovered the specific moderating mechanisms. Longer videos with positive titles received higher numbers of likes and comments. For short videos related to government handling and guidance for stakeholders, positive titles received more shares. Videos related to the latest news received more likes when the title had a higher level of positive emotion. Public health departments should create shorter videos with longer titles, with content focused on the government’s handling of the crisis and guidance for stakeholders. Moreover, in the future, video producers should consider the emotional valence of titles and align it with the content type and video length.