The complex geographical scenario of Mexico allowed the cultural diversification and development of multiple cultures such as Tolteca, Teotihuacan, Mexica, and Maya, among others. Despite this rich cultural heritage, radiometric dating of Mexican cultural samples with radiocarbon (14C) began only in the 1980s and with accelerator mass spectrometry (AMS) in 2013. Analysis of 14C with AMS is the most widely used technique to date archaeological objects and cultural heritage. Since 2013, the Accelerator Mass Spectrometry Laboratory (LEMA) facility of the Institute of Physics at UNAM (IF-UNAM) has supported archaeological research in Mexico, but also investigation in other areas such as geology, physics, chemistry, and environmental sciences through the analysis of 14C, 10Be, 26Al, 129I, and Pu. The absolute dating with 14C continues to be the core of LEMA’s work, where different geographical scenarios of the country and climatic conditions present very diverse analytical challenges. This work presents a basic description of the AMS system of the LEMA laboratory and describes some applications that are currently being developed.

Pelagic seabird populations have declined strongly worldwide. In the North Atlantic there was a huge reduction in seabird populations following the European colonization of the Azores, Madeira and Canary archipelagos but information on seabird status and distribution for the subtropical region of Cabo Verde is scarce, unavailable or dispersed in grey literature. We compiled and compared the historical and current distribution of all seabird species breeding in the Cabo Verde archipelago, updated their relative abundance, investigated their inland habitat preferences, and reviewed their threats. Currently, the breeding seabird community in Cabo Verde is composed of Bulwer’s Petrel Bulweria bulwerii, White-faced Storm-petrel Pelagodroma marina aedesorum, Cape Verde Shearwater Calonectris edwardsii, Cape Verde Storm-petrel Hydrobates jabejabe, Cape Verde Petrel Pterodroma feae, Boyd's Shearwater Puffinus lherminieri boydi, Brown Booby Sula leucogaster, and Red-billed Tropicbird Phaethon aethereus. One breeding species is currently extinct, the Magnificent Frigatebird Fregata magnificens. The relative abundance of Cape Verde Shearwater, Boyd’s Shearwater, Cape Verde Petrel, and Cape Verde Storm-petrel was determined from counts of their nocturnal calls in Santo Antão, São Vicente, Santa Luzia, Branco, Raso and São Nicolau. Cape Verde Petrel occurred only on mountainous islands (Santo Antão, São Nicolau, Santiago, and Fogo) from mid-to high elevations. Larger species such as the Cape Verde Shearwater and Boyd’s Shearwater exhibited a wider distribution in the archipelago, occurring close to the coastline but at lower densities on populated islands. Small procellariforms such as the Cape Verde Storm-petrel occurred at high densities only on rat-free islets and in steep areas of main islands where introduced cats and rats are unlikely to occur. The main threats to seabird populations in Cabo Verde range from predation by introduced predators, habitat alteration or destruction, and some residual human persecution.

Agroforestry systems can play an important role in mitigating the effects of climate change given their capacity to increase tree diversity and to store more carbon than conventional farming. This study aims at assessing carbon stocks and the use of shade trees in different coffee growing systems in the Northeast Peruvian Amazon. Carbon stocks in trees were estimated by field-based measurements and allometric equations. Carbon stocks in dead wood, litter and soil (upper 60 cm) were determined using field sampling and laboratory analysis. The diversity analysis drew on the Shannon–Weiner diversity index, and focus groups were used to obtain information about the local use of shade trees. The total carbon stock in the polyculture-shaded coffee system was 189 t C/ha, while the Inga-shaded and unshaded systems totalled 146 and 113 t C/ha, respectively. The soil compartment contributed the largest carbon stock in the coffee growing systems and contained 67, 82 and 96% of the total carbon stock in the polyculture-shaded, Inga-shaded and unshaded coffee systems, respectively. The Shannon–Weiner index and tree species richness values were highest for the polyculture-shaded coffee system, with a total of 18 tree species identified as important sources of fodder, food, wood, firewood and medicine. Therefore, coffee agroforestry systems play a significant role in carbon storage, while promoting conservation of useful trees in agricultural landscapes in the Peruvian Amazon.

This work examines the impact of the inverse chirp z-transform (ICZT) for frequency-to-time-domain conversion during image reconstruction of a pre-clinical radar-based breast microwave imaging system operating over 1–8 GHz. Two anthropomorphic breast phantoms were scanned with this system, and the delay-multiply-and-sum beamformer was used to reconstruct images of the phantoms, after using either the ICZT or the inverse discrete Fourier transform (IDFT) for frequency-to-time domain conversion. The contrast, localization error, and presence of artifacts in the reconstructions were compared. The use of the IDFT resulted in prominent ring artifacts that were not present when using the ICZT, and the use of the ICZT resulted in higher contrast between the tumor and clutter responses. In one of the phantoms, the tumor response was only visible in reconstructions that used the ICZT. The use of the ICZT evaluated with a time-step size of 11 ps resulted in the reduction of prominent artifacts present when using the IDFT and the successful identification of the tumor response in the reconstructed images.

San Miguel de Allende, a city of 171,857 located in the state of Guanajuato, Mexico, most often appears in media outlets in laudatory publicity, advertising this urban space as perfect for voluntary “lifestyle” immigration and tourism both foreign and national. This article addresses the social tensions, fissures, and paradoxes that emerge from specific auralities of San Miguel's temporary residents. Their romanticized reception of traditional Indigenous danza performances contrasts sharply with the perceived noise of hip-hop in the town's historic center. As more and more residents hailing from outside San Miguel search for their own versions of “small town Mexico,” the racialized experiences of young sanmiguelenses are invisibilized in the overwhelmingly positive reception of Indigenous danzas. The championing of mestizaje as the sole visage for Mexican modernity leaves a convenient space for transnational racism located at the nexus of racialized economic privilege and colonial imagination. In this purportedly post-racial ideological context, how can the analysis of settler-colonizer aurality uncover the racialized structures that undergird the nation-state's management of cultural tourism?

Xenarthra is an endemic South American lineage of mammals, probably the sister clade of the other placental mammals. The oldest records of Xenarthra are from the latest Paleocene, although its current diversity is much lower than that recorded in some intervals of the Cenozoic Era. A new Neogene Xenarthra (Pilosa and Cingulata) assemblage from two localities of the Argentine Eastern Puna (Calahoyo and Casira) is described. The newly recorded taxa—Cingulata, Dasypodidae, Eutatini: Stenotatus sp. indet. and Eutatini indet., Euphractini: Macrochorobates scalabrinii (Moreno and Mercerat, 1891), and Tardigrada, Mylodontinae: cf. Simomylodon sp. indet. and Simomylodon cf. S. uccasamamensis Saint-André et al., 2010—and those already published from Calahoyo—Cingulata: Macrochorobates chapadmalensis (Ameghino, 1908), Eosclerocalyptus sp. indet., and Tardigrada, Megatheriidae: Pyramiodontherium bergi (Moreno and Mercerat, 1891)—suggest a middle–late Miocene age for the fossil-bearing levels. In Calahoyo, the presence of Stenotatus sp. indet., in addition to some rodents currently under study in the lower levels, suggest a closer similarity with the palaeofauna of Cerdas (southern Bolivia), probably involving the last part of the Miocene Climatic Optimum. The Xenarthra recorded in the middle and upper levels of Calahoyo and Casira suggest a late Miocene–Pliocene age. A comparative analysis between Calahoyo and Casira highlights the absence of Cingulata in the latter and a high diversity in the former. This situation probably indicates different paleoenvironmental conditions. Finally, we present the first certain record of the genus Simomylodon Saint-André et al., 2010 in Argentina, which includes the oldest record of dermal ossicles for sloths in South America.

Different nanostructures such as: CuOH nanorods, CuO nanosheets and Cu2O nanograins were obtained by anodization approach at room temperature during times from 10 to 40 minutes. By scanning electron microscopy technique, it was found that Cu2O nanograins were formed at 10 minutes, CuO nanosheets vertically oriented on nanograins were observed at 20 and 30 minutes, and from 20 minutes CuOH nanorods with low vertical orientation on nanosheets were formed, coexisting the three types of nanostructures at the same system. In samples without thermal treatment were observed that Raman spectra of nanograins have a typical signal at 218 cm-1 associated to Cu2O, Raman spectra of nanosheets have signals at 287 and 630 cm-1 associated to CuO and Raman spectra of nanorods, it was observed that Raman spectrum is dominated by an intense signal associated to CuOH located around 488cm-1. In addition, after 3 hours of thermal treatment at 300 °C, the morphology was conserved, and the hydrogen-related compound decreased. Raman spectra of nanorods only presented a signal at 287 cm-1 associated to CuO whereas in nanosheets three peaks at 150, 218, 304 cm-1 associated to the Cu2O were observed.

Collagen associated with bone samples is frequently used for radiocarbon (14C) dating of bones recovered from archaeological sites. However, submersion and exposure to moisture favors the degradation of collagen, which leads to difficulty in reliably dating bones from tropical, humid, or previously submerged archaeological sites. In this paper, we characterized the preservation state of a series of bones, through parameters such as %C, %N, C/N ratio, and collagen recovery. We performed 14C analyses of three collagen fractions obtained through the pretreatment steps (total, ultrafiltered, and insoluble collagen) in order to link the preservation state and the reproducibility of 14C values obtained from the three fractions. Collagen ultrafiltration resulted in a decrease of C/N ratio, although collagen yield was reduced. When two or three collagen fractions were obtained, ages were reproducible and consistent with expected values, according to archaeological or hydrogeological criteria. The pretreatment steps were monitored by infrared spectroscopy in order to analyze the collagen fractions at the molecular level. The presence of collagen in the total and insoluble fractions was confirmed. Since many of the Mexican samples had poor ultrafiltered collagen yield (<3%) or nonexistent yield, our results show that if additional contextual information is carefully considered, the remnant collagen in the total and insoluble fraction can be dated, especially from sites where no other datable fraction exists.

The Nevado de Toluca is a stratovolcano located in the southwest of the Toluca Valley in central Mexico. At a height of around 4200 m there are two crater lakes: El Sol and La Luna. Since Precolumbian times, people in the surrounding valleys carried out rituals and deposited offerings into the lakes. After the Spanish conquest, these rituals were kept alive clandestinely. Currently, reminiscent of Mesoamerican rituals subsist. Due to the long duration of the ritual at the Nevado de Toluca, it is important to date the materials recovered in the underwater and terrestrial archaeological explorations. This article proposes a chronology of Prehispanic ritual activities performed in the Nevado de Toluca based on the characterization and radiocarbon (14C) dating performed to materials from the volcano’s lakes.

A new species of toxodontid notoungulate, Xotodon maimarensis n. sp., is described from the Maimará Formation (late Miocene–early Pliocene), Jujuy Province, northwestern Argentina. This is the first record of a toxodontid from the Eastern Cordillera. The specimen is housed at the Museo de Geología, Mineralogía y Paleontología, Instituto de Geología y Minería de la Universidad Nacional de Jujuy. It consists of an incomplete mandible preserving the right mandibular ramus with part of the dental series, partially preserved symphysis with all the incisors, and a small portion of the left ramus without teeth. The following characters distinguish it as a new taxon: symphysis long and narrow with slight divergence of its lateral borders; strong procumbence of lower incisors and deeply implanted i3; chin angle lower than in X. major and X. cristatus and bulging labial keel limiting strong lateral concavities. Comparative analysis in the context of the recently revised Neogene Toxodontidae indicates that the Maimará specimen shares mandibular features and dental characters with Xotodon and Mixotoxodon, differing from the latter by the more upraised symphysis. The phylogenetic position of Xotodon maimarensis n. sp. supports the taxonomic interpretation of the studied specimen as a new species of Xotodon. This new Toxodontidae increases the knowledge of the diversity and radiation of this group of notoungulates in northwest Argentina.