Universidad de Magallanes
Not a member yet
1947 research outputs found
Sort by
Corrigendum to “Forest Hydrology in Chile; paste, present, and future" (vol 616, 128681, 2023)
No full textThe authors regret to ask for a change an author affiliation. Specifically, author Alejandra Stehr affiliation should be change it to: Departamento Ingeniería Civil, Facultad de Ingeniería, Universidad de Concepción, Concepción, Chile. The correction has been shown above. The authors would like to apologise for any inconvenience caused
Commons of the South: Ecologies of Interdependence in Local Territories of Chile
No full textIn a context of global social-ecological crises, a growing number of researchers, policymakers, activists and politicians have given importance to the "commons". This is mainly because the commons are associated with a logic of regulation and collective organization over the use and conservation of those goods considered essential for both human and ecosystem co-existence. This article seeks to draw attention to the commons from the standpoint of an ecology of interdependence and understand their modes of co-existence in the Global South. We analyze four case studies along with the tensions and junctures faced by the communities and the goods that sustain their continuity over time in southern Chile, a territory where extractivism and resource exploitation have increased over the last decades. The case studies use a combination of qualitative methodologies, including document analysis, literature review, ethnographies, participant observation, interviews and other means of participatory action research with community actors. Integrative analysis and discussion of the results reveal the fluidity and dynamism of the commons of southern Chile in contexts where there is pressure for their institutionalization and/or privatization, as well as various forms of resistance on the part of the territories for their protection and revitalization
Neotropical ornithology: Reckoning with historical assumptions, removing systemic barriers, and reimagining the future
No full textLay Summary center dot Research conducted by ornithologists living and working in Latin America and the Caribbean has been historically and systemically excluded from global scientific paradigms, ultimately holding back ornithology as a discipline. center dot To avoid replicating systems of exclusion in ornithology, authors, editors, reviewers, journals, scientific societies, and research institutions need to interrupt long-held assumptions, improve research practices, and change policies around funding and publication. center dot To advance Neotropical ornithology and conserve birds across the Americas, institutions should invest directly in basic field biology research, reward collective leadership, and strengthen funding and professional development opportunities for people affected by current research policies. A major barrier to advancing ornithology is the systemic exclusion of professionals from the Global South. A recent special feature, Advances in Neotropical Ornithology, and a shortfalls analysis therein, unintentionally followed a long-standing pattern of highlighting individuals, knowledge, and views from the Global North, while largely omitting the perspectives of people based within the Neotropics. Here, we review current strengths and opportunities in the practice of Neotropical ornithology. Further, we discuss problems with assessing the state of Neotropical ornithology through a northern lens, including discovery narratives, incomplete (and biased) understanding of history and advances, and the promotion of agendas that, while currently popular in the north, may not fit the needs and realities of Neotropical research. We argue that future advances in Neotropical ornithology will critically depend on identifying and addressing the systemic barriers that hold back ornithologists who live and work in the Neotropics: unreliable and limited funding, exclusion from international research leadership, restricted dissemination of knowledge (e.g., through language hegemony and citation bias), and logistical barriers. Moving forward, we must examine and acknowledge the colonial roots of our discipline, and explicitly promote anti-colonial agendas for research, training, and conservation. We invite our colleagues within and beyond the Neotropics to join us in creating new models of governance that establish research priorities with vigorous participation of ornithologists and communities within the Neotropical region. To include a diversity of perspectives, we must systemically address discrimination and bias rooted in the socioeconomic class system, anti-Blackness, anti-Brownness, anti-Indigeneity, misogyny, homophobia, tokenism, and ableism. Instead of seeking individual excellence and rewarding top-down leadership, institutions in the North and South can promote collective leadership. In adopting these approaches, we, ornithologists, will join a community of researchers across academia building new paradigms that can reconcile our relationships and transform science. Spanish and Portuguese translations are available in the
HABILIDADES COMUNICATIVAS Y LA PRÁCTICA PEDAGÓGICA EN ESTUDIANTES DE LA CARRERA DE PEDAGOGÍA DE LA UNIVERSIDAD DE MAGALLANES
No full textThe current investigation aimed to determine the communication skills and the pedagogical practice of students of the pedagogy career at the University of Magallanes, Chile. Likewise, it was circumscribed under the gaze of the quantitative approach in the basic typology with a non-experimental design, with a population of 75 students of the pedagogy career studying the pedagogical practice subject and with the management of an unintentional probabilistic sample for a total of 75 subjects. For the collection of information, the survey and a questionnaire with a Likert scale were used. It was validated by the opinion of specialists knowledgeable about the subject in communication skills and pedagogical practice and for reliability through Cronbach's Alpha. The study showed that students consider that teachers expand critical thinking, which is why they inquire that the student learn what is taught and can put it into practice as well as the coexistence of a collaborative work based on the activities that must be developed in the subject of pedagogical practice
A polar insect's tale: Observations on the life cycle of Parochlus steinenii, the only winged midge native to Antarctica
No full textAntarctica and the sub-Antarctic islands include some of the world's most extreme and pristine terrestrial habitats. While they are characterized by low biodiversity and terrestrial communities that are comprised of small, often microscopic, noncharismatic species, they have become a focus of studies of adaptation and biological function in the face of multiple extreme environmental stresses (Convey & Biersma, 2023). Furthermore, they are highly sensitive to climate change and are considered natural laboratories to study and understand its impacts on biota (Contador et al., 2015; Convey & Peck, 2019). In the second half of the 20th century, the maritime Antarctic experienced considerable warming (Turner et al., 2014), causing deglaciation and the development of new ice-free areas and freshwater habitats, both along the coast and inland (Nędzarek & Pociecha, 2010), a process that is expected to continue (Lee et al., 2017). While the regional warming trends paused in the early 21st century (Turner et al., 2016), they are predicted to resume through the rest of the century (Bracegirdle et al., 2020), and a recent botanical study from Signy Island (South Orkney Islands) suggests this may already be happening (Cannone et al., 2022). Maritime Antarctic lakes can experience extremely rapid physical ecosystem change, even magnifying the very rapid (in global terms) regional air temperature increases (of up to 2°C in mean annual air temperature) (Quayle et al., 2002, 2003). The lakes, streams and terrestrial habitats that make up Antarctica's land-based ecosystems are generally oligotrophic, small, and isolated. Many of their small invertebrates, lichens and microbes are found nowhere else on Earth (Convey et al., 2020; Convey & Biersma, 2023; Vincent & Laybourn-Parry, 2008). Other than the scavenging snowy sheathbill (Chionis albus), closely associated with marine vertebrate aggregations, the Antarctic terrestrial fauna consists only of small invertebrates, with just two native species of holometabolous insects, Parochlus steinenii Gercke, 1889 and Belgica antarctica Jacobs, 1900 (Diptera: Chironomidae), and two established nonnative species, Eretmoptera murphyi Schäffer, 1914 (Chironomidae) and Trichocera maculipennis Meigen, 1818 (Trichoceridae) (Convey & Block, 1996; Kozeretska et al., 2021; Potocka & Krzemińska, 2018; Volonterio et al., 2013). Of these, the terrestrial B. antarctica is strictly endemic to coastal regions of the western Antarctic Peninsula and the South Shetland Islands. In contrast, P. steinenii is not found on the Antarctic Peninsula, but occurs throughout the South Shetland Islands in the maritime Antarctic, sub-Antarctic South Georgia and the sub-Antarctic Magellanic ecoregion of southern South America (Contador et al., 2020; Gañan et al., 2021). Its larvae and pupae are aquatic, inhabiting lakes and streams, while the winged adults are terrestrial (Figure 1). As parts of Antarctica undergo some of the most rapid changes worldwide in air temperature, glacial cover, and lake seasonality, polar flies face extreme changes in their environments. Insect life histories are influenced by changing temperatures, from physiology through development and voltinism (number of generations per year) to population dynamics and range (Contador et al., 2014). Climate change has significantly influenced the phenological patterns, distribution, and physiological adaptations of multiple species in different parts of the planet. Those distributed in alpine, subpolar, and polar regions are particularly affected (Walther et al., 2002). Studies of the life history, phenology, and stress tolerances of insects inhabiting aquatic ecosystems in these regions are critical for a better understanding of the ecological consequences of recent and ongoing climate change. Antarctica's native and often endemic terrestrial invertebrate species appear particularly flexible in terms of their life history and ecophysiological strategies (Convey, 1996; Convey & Block, 1996). For example, recent studies have shown that P. steinenii has a wide thermal tolerance, ranging from −5 to +31°C (Contador et al., 2020; Pertierra et al., 2021), which could be an evolutionary consequence of the considerable magnitude of both short- and long-term variation in microenvironmental conditions within their habitats. However, while B. antarctica has been extensively studied as a model organism for a better understanding of the adaptations to extreme environments (Kozeretska et al., 2021), there has been much less research focused on P. steinenii, although studies of its phylogeny, physiology, and distribution patterns have increased in recent years (Allegrucci et al., 2006; Contador et al., 2020; Gañan et al., 2021; Pertierra et al., 2021). These species are of particular interest in terms of their ability to adapt and respond to changing environmental conditions, potentially being sentinel species of the ecosystem consequences of human-induced global environmental change (Kozeretska et al., 2021). In this context, we characterized the habitat preferences, life cycle, and phenology of P. steinenii, the winged Antarctic midge, to better understand how climate change may affect the phenological patterns of this species through time and space. We studied the habitat preferences and the life history of P. steinenii in Lake Kitiesh, Fildes Peninsula, King George Island (62° S, Maritime Antarctica; Figure 1D) over the austral summer seasons from 2014 to 2019, during short (several weeks) field expeditions organized by the Chilean Antarctic Institute (INACH); longer duration, including year-round, field sampling is not possible at this location due to logistic limitations, as is commonly the case in Antarctic field research. This lake hosts an abundant population of P. steinenii and is easily accessible from Professor Julio Escudero Station (INACH, Chile), allowing for continuous site monitoring during the expeditions and the deployment of year-round environmental monitoring equipment. Ice-free areas on King George Island include many temporary shallow meltwater ponds and permanent lakes (typically smaller than 100 m2), which are generally ice covered for the majority of the year (Kim et al., 2020). Surrounding ice-free terrestrial habitats in their catchments are characterized by rich herb–moss communities including the Antarctic hairgrass Deschampsia antarctica and a diverse moss and lichen community. Antarctic populations of P. steinenii are restricted to permanent deeper lakes, which are ice covered for 9–10 months each year, and are surrounded by ice-free areas (Contador et al., 2020; Hahn & Reinhardt, 2006). To characterize the terrestrial habitat in which adults are found, we established five line transects around the perimeter of Lake Kitiesh (Figure 1D). Two transects were located parallel to the main inflow and outflow streams, while the other three were oriented approximately in N, NE and S directions, in each case perpendicular to the lake and starting at the lake edge. Along each transect, we quantified adult densities using 50 × 50 cm quadrats (subdivided into 10 × 10 cm grids) at 0, 2, 4, and 6 m from the lake shore. Adults of P. steinenii were not observed beyond 6 m from the lake edge. Numbers of adult flies in each 10 × 10 cm grid were recorded, and a digital photograph of each entire quadrat was taken to allow assessment of habitat preferences (Canon PowerShot D20). We recorded rock, snow, mud, moss, and water proportions within each quadrat. We assessed differences in P. steinenii adult density around the lake shore using permutational multivariate analysis of variance (PERMANOVA), based on a Bray–Curtis similarity matrix. We also investigated the relationship between P. steinenii density (individuals/m2) and habitat type (rock, snow, mud, moss, and water) using distance-based linear models (DistLM). Both analyses were run in PRIMER-E v7 with Permanova+add-on (Anderson, 2005). The data obtained indicated that P. steinenii adults aggregated at the lake edge, where they reproduce during the austral summer, the females laying batches of eggs at the bases of rocks and stones at the shoreline (Hahn & Reinhardt, 2006). Densities were significantly different at 0, 2, 4, and 6 m distance from the lake shore (p = 0.001, 999 unique permutations, PERMANOVA), being greatest at the shoreline, where they averaged 200 individuals/m2 and reached a maximum of 500 individuals/m2. Density decreased significantly as little as 2 m from the shoreline (mean 35 individuals/m2), and further to 17 individuals/m2 at 4 and 6 m from the shoreline. To visualize densities and habitat preferences, a nonmetric multidimensional scaling analysis (nMDS) was performed, and the habitats assessed were overlaid in the nMDS as vectors (Pearson correlations) (Figure 2C). This indicated that adult flies preferred large rocks adjacent to the shoreline, particularly those oriented to protect them from exposure to wind and snow. Adults were also associated with moss patches, mainly at 2 and 4 m from the shoreline, and were rarely associated with mud (DistLM, R2 = 0.44). To assess the thermal characteristics of the aquatic environment in which P. steinenii develops from egg to adult, we anchored one temperature data logger (HOBO U22 Water Temp Pro V2) at a depth of 50 cm in Lake Kitiesh, corresponding to the depth at which high densities of larvae are commonly found during the austral summer. Minimum, maximum, and average daily water temperature (°C) were recorded from January 2014 to January 2019. Using these data, we calculated growing degree days (GDD), using the pollen package in R (Nowosad, 2019; R Core Team., 2021), which calculates GDDs available for development as the accumulated product of time and temperature above 0°C (noting that lake water temperatures are not likely to exceed the upper developmental temperature of P. steinenii, although this has not been formally assessed and that the larvae do not survive freezing) using daily maximum and minimum temperature data (Baskerville & Emin, 1969; Nufio & Buckley, 2019). To describe the life cycle of P. steinenii, we collected reproductive adults (n = 200) from rocks along the lake shore. Small rearing chambers (10 containers of 250 ml) were set up under controlled temperature conditions (4°C) in the laboratory of Professor Escudero Station as described by Harada et al. (2014). Each rearing chamber contained lake sediment, rocks, and water from the midge's habitat. Groups of ~20 reproductive adults were placed in each container, where mating occurred followed by oviposition on the surface of the rocks. The egg masses were then transported in the rearing chambers to the Wankara Laboratory (Universidad de Magallanes) in Puerto Williams, Navarino Island, Chile. At the Wankara Laboratory, the chambers were maintained in an incubator with a 16 h light and 8 h dark cycle (LD = 16 h:8 h) at ~4°C (range achieved 4–4.5°C), monitored by a temperature logger (Hobo U22 Water Temp Pro V2) recording from the first day of observation until the hatching of the adults. Weekly observations of larval development were made until they reached the adult stage. Larval instar was assigned based on size, initially by eye and then followed by detailed measurements of head width and length (mm) using a microscope with a built-in camera (Leica DM750), calibrated for each image. Head capsule length (mm) was measured from the anterior margin of the frons to the posterior margin of the head's sclerites, while the width (mm) was measured as the distance across the eyes on the head capsule. This enabled larval development to be followed through four distinct developmental instars (L1, L2, L3, L4) (see Appendix S1). Growing degree days (GDDs, thermal units) needed to complete a cycle from egg to adult were then calculated. We obtained the GDDs required for each developmental stage and compared these with the GDD accumulation curve obtained from the water temperature recorded at 50 cm depth in Lake Kitiesh between 2014 and 2019. In the laboratory, after oviposition, a total of 53 eggs hatched close together after 109 GDDs and the L1 required 326 ± 55 (n = 40) GGDs to reach the next molt, with L2, L3, and L4 requiring ~65 ± 11 (n = 38), 77 ± 8 (n = 34) and 192 ± 31 (n = 32) GDDs, respectively. The pupal stage required 166 ± 38 (n = 29) GDDs, meaning that the overall development from oviposition to adult emergence required 1056 ± 41 (n = 12) GDDs (Figure 2A). Similarly, in a simple preliminary laboratory trial in a varying temperature environment (6–12°C) overall development took ~1210 GDDs. Using the temperature data obtained from the natural lake habitat at 50 cm depth, the accumulation of ~1200 GDDs took 4 years. We therefore hypothesize that P. steinenii requires a multiyear life in this habitat at present. Furthermore, GDDs accumulated rapidly during only a short period in the austral summer (December–April) (Figure 2A) during which, we assumed, most biological activity (i.e., larval growth, pupation, adult hatching) would occur. However, we recognize that the larvae may move between different microhabitats in the lake benthos and thereby experience conditions that differ from those at the 50-cm depth where we obtained our lake temperature data. For instance, as oviposition takes place on rocks at the lake edge, hatching L1 will enter very shallow and likely warmer water before moving to greater depths. Hahn and Reinhardt (2006) noted that, in the very shallow water at the lake edge, larvae may complete the first two instars before experiencing their first winter. However, before winter they need to move to deeper parts of the lake in order to survive (Rauschert, 2008), and where they avoid ice formation which is fatal (Contador et al., 2020; Shimada et al., 1991). The extent to which larvae show coordinated or timed movements to and from deeper or shallower water is yet to be investigated. Thus, the balance between time spent at deeper and colder, and shallower and warmer, depths has the potential to both accelerate or decelerate development relative to the 4 years estimated here, and requires further research. However, the fact that all developmental stages were active together in Lake Kitiesh during the austral summers of our study is consistent with the presence of multiple overlapping generations. We found that P. steinenii can be extremely abundant at the local scale. However, at the same time, it is very restricted in terms of its preferred microhabitat distribution. The adult stage is only found along the edges of Antarctic lakes, using rocks and mosses to protect it from harsh environmental conditions, and often most obvious when forming swarms on the ground (Figure 2B,C). While it is capable of flight, for instance being attracted to lit windows of research stations, in our field observations we did not note that adults were flying, rather they were mainly walking and present in large aggregations at ground level. During more windy conditions, we noted that adults sometimes were transported to areas further than 6 m from the lake shore, but such events occurred infrequently. Even though this fly is winged, such observations have suggested that aerial dispersal is a rare occurrence, which is consistent with the complete lack of records of vagrant individuals from the neighboring northern Antarctic Peninsula, which is only 90 km away and to where prevailing westerly winds might be expected to carry it. Additionally, paleolimnological evidence suggests that the species has not previously occurred in the northeast Antarctic Peninsula (Gibson & Bayly, 2007). Such a lack of aerial dispersal may also indicate that the populations of different lakes and islands in the South Shetland Islands may be more isolated in an evolutionary context than might be expected from their apparent physical proximity. However, while Allegrucci et al. (2006) gave a preliminary estimate that South Shetland Islands populations of the species have been isolated from those in South Georgia and southern South America for ~2 million years or more, ongoing molecular phylogeographic studies have yet to examine the differentiation between populations at finer spatial scales. Given these constraints, we asked three key questions as a basis for future research: (1) How could climate change affect the species' phenological patterns? (2) What is the potential of P. steinenii to be able to move and disperse beyond its current distribution in the maritime Antarctic? and (3) What could the impacts of climate change be on this species, given its highly restricted and specialized microhabitat characteristics? Phenological patterns are changing worldwide due to global environmental change. Many cold environment insect species have long life cycles, resulting from very slow growth, repeated or prolonged periods of dormancy, or very long-lived adults (Danks, 1992). Among the invertebrate fauna, insects are strongly affected by thermal variation, as the thermal environment directly affects their growth rates and maturation, and their ability to survive when temperatures exceed their tolerance range. Accumulating evidence suggests that climate change affects the phenology, population sizes, distribution ranges, development, and activity of insects at all trophic levels, resulting in temporal decoupling that may in turn lead to population crashes or extinctions (Nufio & Buckley, 2019; Parmesan, 2006, 2007). In particular, Arctic Chironomidae often have life cycles extending over several seasons (Hodkinson et al., 1996) and adult emergence is highly synchronous, often triggered by rising temperatures (Butler, 1980). For P. steinenii we observed a synchronous pattern of emergence, extending through the austral summer (Figure 2A). Synchronous emergence appears to be an important adaptation to the harsh environmental conditions in Antarctic Chironomidae, as it is in Arctic insects. In this context, the physiological mechanisms for synchronization must be particularly effective, as cohorts may develop over several years allowing the opportunity to diverge in growth and development (Butler, 1980). The possession of an obligate diapause, particularly in the pupal stage, presents one mechanism by which emergence synchrony may be restored. However, the presence of diapause does not appear to have been specifically investigated in this species. Our own preliminary laboratory observations in a simple and thermally variable culture experiment did not suggest the presence of obligate developmental arrest in any life stage, but we did not attempt any temperature manipulation to mimic the presence of, for instance, a seasonal cooling cue activating a diapause phase. One of the many species' traits that has been used to link climate change to phenological shifts is the thermal requirement for development, which can be measured using GDD (Cayton et al., 2015). Integrating GDD data into models aimed at forecasting the impact of current climate change provides a powerful tool for assessing its effects on insect phenology, as it can account for both regional and temporal variations in temperature (e.g., Hughes et al., 2013). We established the first long-term study to improve our understanding of the ecology and life history of P. steinenii. It is already known that freshwater ecosystems in the maritime Antarctic may be strongly affected by climate change (Quayle et al., 2003). Therefore, the voltinism patterns and habitat suitability of P. steinenii could also be severely impacted. Further studies are now required to explore how phenological patterns and voltinism could be affected under different climate change scenarios, using GDDs to predict changes across space and time in the maritime Antarctic. Dispersal is another major life history trait and is particularly important in changing and extreme environments (Lakovic et al., 2017; Waters et al., 2020). We observed that P. steinenii has a very restricted microhabitat distribution, with the apparently rare occurrence of aerial dispersal events. These observations are especially important because migration toward more suitable regions is a common response to climate change (Arenas et al., 2012). Hence, the lack of dispersal capacity in this flying insect may increase its sensitivity to landscape/environmental variation, manifested by a reduced gene flow between even local populations, potentially driving speciation, and increasing susceptibility to extinction. Placed in the context of more general awareness of Antarctic terrestrial diversity as well as the need for its protection, it is notable that most visitors to Antarctica are generally attracted by its charismatic marine fauna (penguins, seals, whales), spectacular scenery, and the all-too-familiar hostility of its environments; they express amazement that the continent's values include terrestrial biodiversity. There is virtually no awareness that Antarctica hosts insects or other terrestrial fauna, such as P. steinenii, or that these provide potentially key sentinels of the consequences of human-induced environmental change. To contribute to the compatibility of the conservation of the populations of this unique Antarctic dipteran in the face of greater intensity of long-term research, we designed nonextractive methods and prioritized ethical considerations in our study. We adapted the biocultural ethics approach to design methods that minimize collection through periods of field observation of behavior and population density (Contador, Rendoll, et al., 2022). Ecosystems and their component biota globally face multiple threats today and, therefore, it is essential to broaden the spectrum of ethical consideration beyond the hi
Surface Solar Extremes in the Most Irradiated Region on Earth, Altiplano
No full textSatellites have consistently pointed to the Altiplano of the Atacama Desert as the place on Earth where the world's highest surface irradiance occurs. This region, near the Tropic of Capricorn, is characterized by its high elevation, prevalent cloudless conditions, and relatively low concentrations of ozone, aerosols, and precipitable water. Aimed at studying the variability of the surface solar irradiance and detecting atmospheric composition changes in the Altiplano, an atmospheric observatory was set up in 2016 at the northwestern border of the Chajnantor Plateau (5,148 m MSL, 22.95°S, 67.78°W, Chile). Here, we report on the first 5 years of measurements at this observatory that establish the Altiplano as the region that receives the highest-known locations. We found that the global horizontal shortwave (SW) irradiance on the plateau is on average 308 W m-2 (equivalent to an annual irradiation of 2.7 MWh m-2 yr-1, the highest worldwide). We also found that forward scattering by broken clouds often leads to intense bursts of SW irradiance; a record of 2,177 W m-2 was measured, equivalent to the extraterrestrial SW irradiance expected at approximately 0.79 astronomical units (AU) from the Sun. These cloud-driven surface solar extremes occur on the Chajnantor Plateau at a frequency, intensity, and duration not previously seen anywhere in the world, making the site an ideal location for studying the response of photovoltaic (PV) power plants to periods of enhanced SW variability
The extreme southern origins of globality: Circumnavigation, habitability, and geopolitics (sept, 10.1017/S1740022822000225, 2022)
No full textAn abstract is not available for this content so a preview has been provided. Please use the Get access link above for information on how to access this content
The center cannot hold: A Bayesian chronology for the collapse of Tiwanaku
No full textThe timing of Tiwanaku's collapse remains contested. Here we present a generational-scale chronology of Tiwanaku using Bayesian models of 102 radiocarbon dates, including 45 unpublished dates. This chronology tracks four community practices: residing short- vs. long-term, constructing monuments, discarding decorated ceramics, and leaving human burials. Tiwanaku was founded around AD 100 and around AD 600, it became the region's principal destination for migrants. It grew into one of the Andes' first cities and became famous for its decorated ceramics, carved monoliths, and large monuments. Our Bayesian models show that monument building ended similar to AD 720 (the median of the ending boundary). Around similar to AD 910, burials in tombs ceased as violent deaths began, which we document for the first time in this paper. Ritualized murders are limited to the century leading up to similar to AD 1020. Our clearest proxy for social networks breaking down is a precise estimate for the end of permanent residence, similar to AD 1010 (970-1050, 95%). This major inflection point was followed by visitors who used the same ceramics until similar to AD 1040. Temporary camps lasted until roughly similar to AD 1050. These four events suggest a rapid, city-wide collapse at similar to AD 1010-1050, lasting just similar to 20 years (0-70 years, 95%). These results suggest a cascading breakdown of community practices and social networks that were physically anchored at Tiwanaku, though visitors continued to leave informal burials for centuries. This generation-scale chronology suggests that collapse 1) took place well before reduced precipitation, hence this was not a drought-induced societal change and 2) a few resilient communities sustained some traditions at other sites, hence the chronology for the site of Tiwanaku cannot be transposed to all sites with similar material culture
Late Pleistocene to Middle Holocene lithic industries from Southernmost Patagonia. Discussing technical variability, continuity and innovations
No full textThe study of early lithic assemblages from South America's Southern Cone used to be strongly focused on projectile points, including the famed fishtail type, often using a typological approach. The last three decades have seen a growing diversifica-tion of theoretical and methodological approaches to lithic studies, as well as new analytical techniques, used to study issues including lithic production systems, technical variability, tool manufacturing and management, raw material economy and circulation, among others. Recent studies on lithic industries are exemplified by discussing Southernmost Patagonia's first human occupations, dated ⠂13,000 cal BP, and Middle Holocene early marine explorations, dated ⠂8000-7000 cal BP. An overview and compar-ison of Southernmost Patagonia's early hunter-gatherer lithic technologies is made.⠃C 2023 Published by Elsevier Masson SAS
A Predictive Current Control Strategy for a Medium-Voltage Open-End Winding Machine Drive
No full textThis paper presents a medium-voltage drive based on an open-end winding induction machine supplied by a multilevel power converter topology. The power converter consists of cascaded two-level three-phase voltage source inverters (VSI) connected to each side of the machine windings and each VSI is fed by an isolated DC supply. The topology has been previously reported in the literature as a sinusoidal pulse-width modulation operating in an open loop. In this work, a closed-loop model predictive control (MPC) strategy is proposed. MPC offers a much simpler method to control the power switches of the inverter compared to complex modulation strategies that are typically used in multilevel converters. Moreover, the advantage of reducing the common-mode voltage offered by the open-end winding configuration is fully exploited in this work. Simulation results are presented to validate the performance of the proposed topology and control method