Seismic shear-wave velocity as a function of depth for generic rock sites has been estimated from borehole data and studies of crustal velocities, and these velocities have been used to compute frequency-dependent amplifications for zero attenuation for use in simulations of strong ground motion. We define a generic rock site as one whose velocity at shallow depths equals the average of those from the rock sites sampled by the borehole data. Most of the boreholes are in populated areas; for that reason, the rock sites sampled are of particular engineering significance. We consider two generic rock sites: rock, corresponding to the bulk of the borehole data, and very hard rock, such as is found in glaciated regions in large areas of eastern North America or in portions of western North America. The amplifications on rock sites can be in excess of 3.5 at high frequencies, in contrast to the amplifications of less than 1.2 on very hard rock sites. The consideration of unattenuated amplification alone is computationally convenient, but what matters for ground-motion estimation is the combined effect of amplification and attenuation. For reasonable values of the attenuation parameter κ0, the combined effect of attenuation and amplification for rock sites peaks between about 2 and 5 Hz with a maximum level of less than 1.8. The combined effect is about a factor of 1.5 at 1 Hz and is less than unity for frequencies in the range of 10 to 20 Hz (depending on κ0). Using these amplifications, we find provisional values of about Δσ = 70 bars and κ0 = 0.035 sec for rock sites in western North America by fitting our empirically determined response spectra for an M 6.5 event to simulated values. The borehole data yield shear velocities (V30) of 618 and 306 m/sec for “rock” and “soil” sites, respectively, when averaged over the upper 30 m. From this, we recommend that V30 equals 620 and 310 m/sec for applications requiring the average velocity for rock and soil sites in western North America. By combining the amplifications for rock sites and the site factors obtained from our analysis of strong-motion data, we derive amplifications for sites with V30 = 520 m/sec (NEHRP class C, corresponding to a mix of rock and soil sites) and V30 = 310 and 255 m/sec (average soil and NEHRP class D sites, respectively). For the average soil site, the combined effect of amplification and attenuation exceeds a factor of 2.0 for frequencies between 0.4 and about 4 Hz, with a peak site effect of 2.4; the peak of the NEHRP class D site effect is 2.7.
Significance North American and European countries built many large dams until 1975, after which both started to abandon a significant part of their installed hydropower because of the negative social and environmental impacts. However, there has been a recent trend of new large hydropower dams being built in developing countries, particularly in megabiodiversity river basins, such as the Amazon, the Congo, and the Mekong. The socioeconomic and environmental damages in these river systems are even greater than the early costs in North America and Europe. This paper discusses how the hydropower sector needs to not only focus on energy production but also, include the negative social and environmental externalities caused by dams and recognize the unsustainability of current common practices. Hydropower has been the leading source of renewable energy across the world, accounting for up to 71% of this supply as of 2016. This capacity was built up in North America and Europe between 1920 and 1970 when thousands of dams were built. Big dams stopped being built in developed nations, because the best sites for dams were already developed and environmental and social concerns made the costs unacceptable. Nowadays, more dams are being removed in North America and Europe than are being built. The hydropower industry moved to building dams in the developing world and since the 1970s, began to build even larger hydropower dams along the Mekong River Basin, the Amazon River Basin, and the Congo River Basin. The same problems are being repeated: disrupting river ecology, deforestation, losing aquatic and terrestrial biodiversity, releasing substantial greenhouse gases, displacing thousands of people, and altering people’s livelihoods plus affecting the food systems, water quality, and agriculture near them. This paper studies the proliferation of large dams in developing countries and the importance of incorporating climate change into considerations of whether to build a dam along with some of the governance and compensation challenges. We also examine the overestimation of benefits and underestimation of costs along with changes that are needed to address the legitimate social and environmental concerns of people living in areas where dams are planned. Finally, we propose innovative solutions that can move hydropower toward sustainable practices together with solar, wind, and other renewable sources.
Significance Amazonia is not only the world’s most diverse rainforest but is also the region in tropical America that has contributed most to its total biodiversity. We show this by estimating and comparing the evolutionary history of a large number of animal and plant species. We find that there has been extensive interchange of evolutionary lineages among different regions and biomes, over the course of tens of millions of years. Amazonia stands out as the primary source of diversity, which can be mainly explained by the total amount of time Amazonian lineages have occupied the region. The exceedingly rich and heterogeneous diversity of the American tropics could only be achieved by high rates of dispersal events across the continent. The American tropics (the Neotropics) are the most species-rich realm on Earth, and for centuries, scientists have attempted to understand the origins and evolution of their biodiversity. It is now clear that different regions and taxonomic groups have responded differently to geological and climatic changes. However, we still lack a basic understanding of how Neotropical biodiversity was assembled over evolutionary timescales. Here we infer the timing and origin of the living biota in all major Neotropical regions by performing a cross-taxonomic biogeographic analysis based on 4,450 species from six major clades across the tree of life (angiosperms, birds, ferns, frogs, mammals, and squamates), and integrate >1.3 million species occurrences with large-scale phylogenies. We report an unprecedented level of biotic interchange among all Neotropical regions, totaling 4,525 dispersal events. About half of these events involved transitions between major environmental types, with a predominant directionality from forested to open biomes. For all taxonomic groups surveyed here, Amazonia is the primary source of Neotropical diversity, providing >2,800 lineages to other regions. Most of these dispersal events were to Mesoamerica (∼1,500 lineages), followed by dispersals into open regions of northern South America and the Cerrado and Chaco biomes. Biotic interchange has taken place for >60 million years and generally increased toward the present. The total amount of time lineages spend in a region appears to be the strongest predictor of migration events. These results demonstrate the complex origin of tropical ecosystems and the key role of biotic interchange for the assembly of regional biotas.
We show AlN/GaN high electron mobility transistors with in situ SiN for passivation and regrown n ^+ GaN ohmic contacts using a selective etching process that is more suitable for device scaling. The regrown ohmic contacts have a clean and sharp edge definition with a contact resistance of 0.25 Ω·mm. The interfacial resistance between the regrown n ^+ GaN and the 2DEG at AlN/GaN interface is 0.058 Ω·mm, close to the theoretical quantum conductance limit. The fabricated devices with a gate length of 0.7 μm exhibit a maximum current density of 1.57 A mm ^−1 and on-resistance of 1.85 Ω·mm at a gate bias of 1 V.
Severine Matheus, Charlotte Balière, Veronique Hourdel
et al.
Background:
Tropical infectious diseases pose a significant burden on global public health, exacerbated by the emergence of new pathogens. French Guiana (FG), a French overseas department in northeastern South America, presents favorable conditions for the emergence of zoonotic pathogens due to its tropical climate and diverse ecosystems. Over the past two decades, various emerging zoonotic pathogens have been detected in patients with severe infections, though, many other severe human infectious diseases remain undocumented.
Aim:
This prospective pilot study aims to identify infectious pathogens responsible for severe infections in French Guiana using routine diagnostic tests and metagenomic approach.
Methods:
This study was conducted from July 2013 to December 2015. It included consenting patients of all ages and sexes admitted to the ICU for severe infections in FG. Biological samples were collected based on clinical presentation (plasma, serum, nasopharyngeal swab, broncho-alveolar liquid, cerebrospinal fluid). All samples were collected in duplicate for routine microbiological tests and potential metagenomic sequencing when initial investigations proved negative.
Results:
During the study period, 10.9% (89/813) of ICU admissions were due to community-acquired sepsis. Of these, 22/89 (24.7%) were enrolled. Routine diagnosis tests identified a causal pathogen in 54.5% (12/22) of cases, including arboviruses, influenza virus, Trypanosoma cruzi, Coxiella burnetti, enterovirus, Histoplasma sp, and Leptospira sp. Five of the 22 patients had an unfavorable outcome. Genomic sequence analyses allowed identification of the first human case of Leptospira santarosai in the region.
Conclusion:
This pilot study underscores the array of pathogens causing severe infections in French Guiana. It emphasizes the need to investigate sepsis of unknown origin in a region susceptible to pathogen emergence or reemergence. [J Microbiol Infect Dis 2024; 14(4.000): 178-185]