PDF superior Life at the dry edge: Microorganisms of the Atacama Desert

Life at the dry edge: Microorganisms of the Atacama Desert

Life at the dry edge: Microorganisms of the Atacama Desert

On the other hand, the underside of translucent stones has been demonstrated to offer an environment protected from the intense radiation typical of deserts. Sequencing 16S rRNA from samples ob- tained from hypolithic biofilms under quartzes showed the pres- ence of members of the gamma, alpha, and beta-Proteobacteria, Actinobacteria, Gemmatimonadetes, Chloroflexi and Cyanobacte- ria, Chroococcidiopsis being the dominant among the latter [33]. This finding is not unexpected, since this genus of unicellular Cya- nobacteria has been described in many dry environments. More- over, it is known that photoautotrophic bacteria play a leading role in desert microbial consortia, since they are responsible for carbon and nitrogen input to the community. Interestingly, it was found that each quartz stone from the same area supported a number of exclusive 16S rRNA gene-defined genotypes, creating effective ‘‘islands of biodiversity’’ in this harsh environment. Most likely this is due to the fact that rocks that are apparently identical differ in light influx, nutrient supply and water availability beneath them.
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7 Lee mas

Discovery and microbial content of the driest site of the hyperarid Atacama Desert, Chile

Discovery and microbial content of the driest site of the hyperarid Atacama Desert, Chile

The Atacama Desert is the driest and oldest desert on Earth. Eleven years ago, the Yungay region was established as the driest site of this hyperarid desert and also close to the dry limit for life on Earth. Since then, much has been published about the extraordi- nary characteristics of this site and its pertinence as a Mars analogue model. However, as a result of a more systematic search in the Atacama here, we describe a new site, María Elena South (MES), which is much drier than Yungay. The mean atmospheric relative humidity (RH) at MES was 17.3%, with the RH of its soils remaining at a constant 14% at the depth of 1 m, a value that matches the lowest RH measure- ments taken by the Mars Science Laboratory at Gale Crater. Remarkably, we found a number of viable bac- terial species in the soil profile at MES using a com- bination of molecular dependent and independent methods, unveiling the presence of life in the driest place on the Atacama Desert reported to date.
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7 Lee mas

Desde el Pacífico a la Foresta Tropical: Redes de Interacción Social en el Desierto de Atacama Durante el Pleistoceno FinalFrom the Pacific to the Tropical Forests: Networks of Social Interaction in the Atacama Desert, Late in the Pleistocene

Desde el Pacífico a la Foresta Tropical: Redes de Interacción Social en el Desierto de Atacama Durante el Pleistoceno FinalFrom the Pacific to the Tropical Forests: Networks of Social Interaction in the Atacama Desert, Late in the Pleistocene

The social groups that initially inhabited the hyper arid core of the Atacama Desert of northern Chile during the late Pleistocene integrated a wide range of local, regional and supra regional goods and ideas for their social reproduction as suggested by the archaeological evidence contained in several open camps in Pampa del Tamarugal (PdT). Local resources for maintaining their every-day life, included stone raw material, wood, plant and animal fibers, game, and fresh water acquired within a radius of ∼ 30 km (ca. 1-2 days journey). At a regional scale, some goods were introduced from the Pacific coast (60-80 km to the west, ca. 3-4 days journey), including elongated rounded cobbles used as hammer stones in lithic production, and shells, especially from non-edible species of mollusks. From the Andes (ranging 80-150 km to the east, ca. 5-8 days of journey), they obtained camelid fiber, obsidian and a high-quality chalcedony, in addition to sharing knowledge on projectile point designs (Patapatane and Tuina type forms). Pieces of wood of a tropical forest tree species (Ceiba spp.) from the east Andean lowlands (600 km away, ca. 30 days of journey) were also brought to the PdT. While local goods were procured by the circulation of people within the PdT, the small number of foreign items would have been acquired through some sort of exchange networks that integrated dispersed local communities throughout several ecosystems. These networks may have been a key factor behind the success exhibited by these early hunter- gatherers in the hyper arid ecosystems of the Atacama Desert at the end of the Pleistocene.
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22 Lee mas

RISE AND DECLINE OF CHINCHORRO SACRED LANDSCAPES ALONG THE HYPERARID COAST OF THE ATACAMA DESERT

RISE AND DECLINE OF CHINCHORRO SACRED LANDSCAPES ALONG THE HYPERARID COAST OF THE ATACAMA DESERT

The study of complex funerary ritual development among hunters and gatherers societies should take into account how people made up for the continuity of their social system without the support of centralized organizations. This research integrates cultural and natural factors to explore how the Chinchorro carried on with their way of life isolated at geographically restricted perennial river mouths with fresh water along the Atacama Desert in the Pacific coast of South America. Within these rather crowded settlings, they created and maintained a social system catalyzed by a complex funerary tradition, embodied by a unique funerary ideological discourse that resulted in the creation of a sacred landscape or “spiritscape”. We argue that the extreme hyperaridity of the coastal Atacama Desert (21º - 17.30º S), and the extraordinary biomass production of the marine littoral constituted a fundamental milieu for the maintenance of their long-term social system. The Chinchorro belief system lasted for several millennia (8,000-4,000 BP), but new ways of life and burial practices followed major changes in the coastal ecosystem they relied on, which would have influenced how the “old tradition” was manifested over time. Conversely, we sustain that these natural “constraints” faced by the Chinchorro along the coast of the Atacama Desert, were influential, in the course of their history or the way they socially organized themselves.
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18 Lee mas

Pollen limitation and reproductive assurance in the flora of the coastal Atacama Desert

Pollen limitation and reproductive assurance in the flora of the coastal Atacama Desert

Comparative analyses by phylogenetically independent contrasts (Felsenstein 1985; Purvis and Rambaut 1995) were performed to examine the relationships between autofertility and life form, between PL and autofertility, and between PL and flower size. A phylogenetic tree of the species in the data set was assembled using the phylogeny of angiosperms at the subfamily level, from the Angiosperm Phylogeny Group (Stevens 2001–). Except Solanaceae, all families in the data set are represented by one or two species, and hence, family information was sufficient to posit the majority of studied species. Solanaceous genera were positioned according to Olmstead and Palmer (1992). Branch lengths were set to unity. Phylogenetic independent contrasts for AFI, PL, and flower size were generated separately, using the PDAP mod- ule (Midford et al. 2003) of Mesquite (Maddison and Mad- dison 2007). AFI and PL were transformed by the arcoseno function. No correlation between the absolute values of the contrasts and their standard deviations were found. To test whether AFI differed between annuals and perennial species, the procedure designed for discrete predictor variables of Purvis and Rambaut (1995) was used. AFI contrasts were an- alyzed using a t-test on the mean of the contrasts. A mean significantly different from 0 indicated that AFI differed be- tween annuals and perennials. To test whether PL decreased with AFI and to test whether PL increased with flower size, Table 1
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9 Lee mas

Isolation of UVC Tolerant Bacteria from the Hyperarid Atacama Desert, Chile

Isolation of UVC Tolerant Bacteria from the Hyperarid Atacama Desert, Chile

However, little has been published on indigenous UV radiation-tolerant microbial populations of the Atacama Desert. An impressive silica-encased filamentous cyanobac- teria was recently found in El Tatio geothermal fields at the Andes Mountains in the Atacama. The silica matrices were suggested to provide cells with an efficient UV shield, without PAR attenuation [22]. In a different study conducted in the dry core (Yungay) of the Atacama Desert, nonnative microorganisms quickly died upon exposure to solar radia- tion at the soil surface [4, 9]. However, when protected by gypsum and mineral grain coverings, survival was extended up to 8 days, suggesting that UV-tolerant microorganisms may be able to survive below the soil surface of the Atacama. One well-known UV-tolerant microorganism which members have been found across the Atacama Desert is Chroococcidiopsis. These cyanobacterial species have been found in endolithic and hypolithic habitats [1, 26]. Besides this Cyanobacterium, there are no reports on the description and further enumeration of UV-tolerant micro- organisms sampled from this Desert. Here, we report on novel bacterial isolates (mainly from the Bacillus genus) collected from different sites of the Atacama. The UV tolerance of one of these isolates is about tenfold that of a wild-type Escherichia coli strain.
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11 Lee mas

Late Pleistocene human occupation of the hyperarid core in the Atacama Desert, northern Chile

Late Pleistocene human occupation of the hyperarid core in the Atacama Desert, northern Chile

Site QM12 is situated atop a small erosional remnant of the late Miocene alluvial fan surface de fi ned as Terrace 1 (T1) by Nester et al. (2007) (Fig. 3). This surface is devoid of vegetation, covered by a desert pavement, and blanketed by a well-developed sulfate soil composed of anhydrite and gypsum. It is situated above the late Pleistocene stream deposits (T2 surfaces) and therefore would have remained dry and afforded a view of the surrounding landscape during the late Pleistocene. The T1 surface probably lacked vege- tation during the occupation of QM12 as there is no evidence for sustained increases in precipitation during the late Pleistocene at this elevation (Nester et al., 2007; Gayo et al., 2012a). During the CAPE, increased stream discharge and widespread deposition of a sequence (T2, T2.5, T2.7) of fl uvial conglomerate terraces occurred in Quebrada Maní and in drainages to the north and south between 17.6 and 11.4 ka (Nester et al., 2007; Gayo et al., 2012a). The late Pleistocene channel (T2.5) of Quebrada Maní was broad ( w 1 km) at this locality and separated by isolated erosional remnants of the T1 terrace (Fig. 3). Leaf litter deposits consisting of Escallonia angusti- folia leaves are common and in many places are buried by hillslope colluvium from the T1 terrace fi lled with gypsum and anhydrite salts. Two samples of these leaf litter deposits yielded calibrated radiocarbon ages of 16.1 and 17.2 ka (Table 1) and indicate the presence of riparian woodlands in these channels. Therefore, the late Pleistocene fl uvial conglomerates pre-date the occupation of QM12. Late Pleistocene wetland deposits overlie the fl uvial con- glomerates to the north of the QM12. Initial radiocarbon dates of these deposits indicate that the uppermost paludal facies are w 17 ka in age and therefore also pre-date human occupation in this area (Workman, 2012).
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12 Lee mas

Extreme environments as potential drivers of convergent evolution by exaptation: The Atacama Desert Coastal Range case

Extreme environments as potential drivers of convergent evolution by exaptation: The Atacama Desert Coastal Range case

A particular trait may not be favored by natural selection, even if it confers increased functional capabilities. To provide a fit- ness advantage, the enhanced capabilities must actually lead to an increase in survival or reproductive success. For the examples shown here, this seems to be the case. One may also consider the time range that took for the first phototrophic species to colonize land. The evolution of the first land plants from land phototrophic species took about 750 million years. In turn, the Atacama has imposed its arid conditions on life for the past 150 million years. Thus, put in a very simplistic way, the collection of adaptations shown by the described Dunaliella, Cyanidium, and Chroococcidiopsis species at the Coastal Range of the Atacama are at the “one fifth milestone” (750/150 my) of the road taken by the ancestors of modern plants. As these three species seem to have crossed the threshold where they are able to live and reproduce on land, they may now be in the evolutionary transit to better adapt to this habitat. If these species are retracing the same path taken by plants, one could expect the next important stage to be the division of tasks in specialized groups of cells, in other words, the origins of mul- ticellularity. Intriguingly, the molecular evidence suggests that Chroococcidiopsis is the closest living relative of filamentous heterocyst-differentiating cyanobacteria (Fewer et al., 2002), with the extant species having reverted to unicellularity. Nonetheless, an important stage in the Chroococcidiopsis cycle is the tetrad stage (Azúa-Bustos et al., 2012) (Figure 6B). One could then test the hypothesis that there is a functional reason for the organization of cells in tetrads. Could this phenomenon repre- sent a potential and initial division of labor? Consistent with the importance of the close arrangement of seemingly simi- lar cells and the origin of multicellularity is a report in which the genome of the multicellular Volvox carteri was compared with the genome of its unicellular relative Chlamydomonas rein- hardtii (Prochnik et al., 2010). This study revealed that increases in complexity seem to be more associated with modifications of lineage-specific proteins than to large-scale development of protein-coding capacity.
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9 Lee mas

Hypolithic cyanobacteria supported Mainly by fog in the Coastal Range of the Atacama Desert

Hypolithic cyanobacteria supported Mainly by fog in the Coastal Range of the Atacama Desert

All together, the light, temperature and relative humidity data shown above allow us to postulate a model that could explain the development of a hypolithic community under quartz stones at this site. Since the fog coming from the Pacific Ocean usually advances inland during late evening and night, water condenses onto all surface types of the Coastal Range hills (Fig. 8). During the day, as the surface gets heated by the sun, water quickly evaporates back to the atmosphere, but with lower rates of evaporation from the slightly cooler quartz rocks. It has been previously shown that other types of rocky material, like gravel, reduce the amount of soil surface in direct contact with the atmosphere, shielding the underly- ing soil from wind and solar radiation, thus favoring moisture conservation [25, 26, 32]. In the Namib Desert, quartz desert pavement showed evidence of enhanced nocturnal cooling, thereby promoting dew formation [17]. This condensation process allows the colonization of quartz by the hypolithic microorganisms, which by producing water-retaining exopolysaccharides start a pos- itive feedback cycle allowing further and more sustained water retention and colonization.
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15 Lee mas

Emergence of social complexity among coastal hunter gatherers in the Atacama Desert of northern Chile

Emergence of social complexity among coastal hunter gatherers in the Atacama Desert of northern Chile

estimate is likely higher than 1% considering that people buried their dead within the living areas, meaning that Chinchorro cemeteries were not separated from domestic areas (3, 41). In Camarones 14, for instance, with the oldest evidence of AM, bodies were buried within the shell midden (41). Chinchorro cemeteries have horizontal rather than vertical stratigraphy (42); burials were usually shallow (less than 50–60 cm), and bodies were interred in close proximity to one another. This implies that (i ) corpses could have become exposed due to erosion, human removal while performing daily day activities, or both, and (ii) living group members would have seen existing mummies at least at burial time and possibly more often if the upper stratum was exposed for some time after placement, owing to long rituals (4). Further, our parameterized demographic model suggests that a typical living individual would have been exposed to tens of deaths during his or her life (roughly 50% of a group of a total size on the order of 50–150 individuals). All of these interrelated facts provide a strong case for Chinchorros experiencing an in- creased scale of previous deaths, the mummies of which would have accumulated over many generations, and the resultant emergence of complex mortuary practices as per our hypothesis (Fig. 2). Once the practice of AM began, it is possible that the location of mummies was marked, as has been observed in pre- pottery Neolithic societies of the Levant, where secondary bur- ials were associated with the removal of the skull, whose location was marked at the time of the initial burial (37).
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7 Lee mas

Phylogeography of two closely related species of nolana from the coastal atacama desert of chile: Post glacial population expansions in response to climate fluctuations

Phylogeography of two closely related species of nolana from the coastal atacama desert of chile: Post glacial population expansions in response to climate fluctuations

The conspicuous latitudinal gradient in both genetic dif- ferentiation and genetic diversity of Nolana – along the transition from hyper-arid to semi-arid – is also supported by genetic landscape analysis and barriers detected by Mon- monier’s algorithm, pointing to marked population differen- tiation at 25–27° S. Northern populations within this species complex also showed the highest number of haplo- types and greater haplotypic and nucleotide diversity, sug- gesting that they have been able to persist for long time. These data support the hypothesis that populations within this species complex remained in northern areas during the glaciations and wet Holocene episodes, when increased run- off or groundwater upwelling could have allowed the expan- sion of local populations of Nolana along creeks and moun- tain slopes, as suggested for lomas vegetation by D ıaz et al. (2012). Exposed seashore as a consequence of lower sea level also favoured population expansion in lowland areas (Faure et al., 2002; Sakaguchi et al., 2010). In fact, Monmo- nier analyses grouped coastal sites S3, S5 and the inland S4 – located in the head of a dry stream bed – together, reflecting past and present interconnections by alluvial fans in coastal Atacama. During Holocene and interglacial arid episodes, populations in the hyper-arid Atacama probably contracted, as a consequence of an overall trend of declin- ing rainfall and groundwater discharge, as well as rising sea Table 1 Genetic diversity of Nolana populations found at the southern margin of the Atacama Desert. Location, latitude, longitude, voucher number, climate, sample size (n) and measurements of genetic diversity for three populations of N. incana, 10 of
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13 Lee mas

Laboratory Manual

Laboratory Manual

pull the retina back from the underlying choroid layer. See the photograph on the right side below. Notice that the retina is only firmly attached to the choroid at one place. This region is the blind spot. Here the nerve fibres leave the retina and form the optic nerve which is directly behind the blind spot.

16 Lee mas

Camoufl-Ages: Body Assemblages at the Time of the Apocalypse

Camoufl-Ages: Body Assemblages at the Time of the Apocalypse

been done with drugs would soon be innate” (OC: 358). But the control over the generation of entire species is only an aspect of Crake’s ambitious projects, because another consistent aspect of lifestyle alteration is the administration of a powerful drug, the BlyssPluss, destined to become “a huge money-spinner” (OC: 348). This super-pill promises some attractive benefits, such as a durable youth, protection against sexually transmitted diseases, and, what most counts, an “unlimited supply of libido and sexual prowess” (OC: 346). This miraculous dietary supplement, however, conceals a serious side effect, which is not illustrated in the patient information leaflet: “The BlyssPluss would also act as a sure-fire one-time-does-it- all birth-control pill, for male and female alike, thus automatically lowering the population level” (OC: 347). The cost in terms of human lives of this attempt at sterilizing “people without them knowing” (OC: 347), will be very high, because it will lead to the break out of a pandemic which has the extreme consequence of mankind's decimation. In this desperate and desolated apocalyptical dimension, Snowman is “the ultimate outcast” (Rao, 2006:108) whose struggle for survival also involves the protection and salvation of Crake’s offspring, after his friend kills Oryx and is killed in turn by Jimmy. In his melancholic evocation of the past and his hazardous explorative expeditions, Jimmy shows an “increasingly suicidal despair” (Jennings, 2010: 16).
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15 Lee mas

On roof geometry for urban wind energy exploitation in high-rise buildings

On roof geometry for urban wind energy exploitation in high-rise buildings

The building sector represents 40% of the European Union’s (EU) total energy consumption. Reducing energy consumption in this area is therefore a priority under the “20-20-20” objectives on energy efficiency [7]. The Directive 2010/31/EU of the European Parliament and of the Council of 19 May 2010 on the energy performance of buildings [8] aims to contribute to this objective by proposing guiding principles for Member States regarding the energy performance of buildings. One of these guidelines concerns the minimum requirements for energy efficiency during the design of new buildings. New buildings shall comply with these requirements and undergo a feasibility study before construction starts, looking at the installation of renewable energy supply systems and other sustainable systems [8], such as wind energy exploitation devices. New software [9] is being developed nowadays for the evaluation of wind energy resources in the urban environment.
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27 Lee mas

Perennial stream discharge in the hyperarid Atacama Desert of northern Chile during the latest Pleistocene

Perennial stream discharge in the hyperarid Atacama Desert of northern Chile during the latest Pleistocene

T he hyperarid Atacama Desert drapes across the western flank of the Andes Mountains, at the western extreme of central South America, including much of northern Chile. The extreme lack of precipitation is a feature that has remained stable over millions of years because of major coupled atmo- spheric and tectonic feedbacks (1–5). But short-lived times of increased precipitation exist in paleohydrological records at elevations above 2,000 m, reflecting millennial-scale variations in global climate. In particular, two major periods of increased precipitation are known to have affected groundwater tables and plant species distributions during the late Quaternary (6–10). The impacts of these wet phases in the lower elevation desert, expressed as either increased precipitation or variations in surface runoff and local groundwater table, have largely re- mained unstudied, although attempts have been made to under- stand current climate and the hydrologic system feedbacks (11–13). Increased surface flow over this region during predom- inantly late Pleistocene humid intervals may have modified the landscape and contributed to groundwater recharge.
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6 Lee mas

Characterization of seed dormancy of Nolana (Solanaceae) in the coastal Atacama Desert of Chile

Characterization of seed dormancy of Nolana (Solanaceae) in the coastal Atacama Desert of Chile

Nolana species have been acknowledged to have high ornamental potential due to their succulent foliage and flowering characteristics (Freyre et al., 2005; Riedemann et al., 2006), but there are other reasons which make the study of this genus particularly interesting. It has a high degree of endemism and presence in habitats with extreme conditions of aridity and salinity, which gives it a high conservation value (Tu et al., 2008, Dillon et al., 2009); also, some species present compounds with fungicidal activity in fungi of agricultural importance (N. sedifolia, Vio-Michaelis et al., 2012). Additionally, the genus belongs to the Solanaceae family and to the Solanoideae sub-family (Olmstead et al., 2008), where tomato and pepper also belong. This makes it a possible source of genes of interest for the development of cultivars that are better adapted to conditions of aridity and/or salinity; these intergeneric hybridizations have been studied and produced in other families such as Brassicaceae (Kaneko and Woo Bang, 2014). However, Nolana species have been poorly studied and there is limited information regarding their ecology, reproductive biology and establishment strategies, knowledge that is essential for their conservation and potential use (but see Freyre et al., 2005; Douglas and Freyre, 2010; Jewell et al., 2012; Cabrera et al., 2015).
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128 Lee mas

Bioethics, bioweapons and the microbiologist

Bioethics, bioweapons and the microbiologist

gy is carried out through bioethics, considered the science of the sur- vival. In the microbiology, there are numerous discoveries related with pathogenic microorganisms, including those that can be used as weapons in a biological war or in an attack considered bioterrorism. The scientist involved in microbiology can participate with his knowledge in the development and improvement of bioweapons, however from the point of view of bioethics it is not acceptable that he works in an investigation related with these topics, because the de- fense research can evolve in offensive one. The war is an antisurvival activity, therefore it is not acceptable. In the same way, the biological weapons composed with virus, fungi or alive bacteria, or with toxins from them, neither they are morally accepted. After the terrorist at- tacks with anthrax in the United States in 2001, the world scientific community in the field of microbiology should show against the use of the microorganisms like bioweapons, at the time of promoting the idea that the responsible use for the microorganisms is a moral impe- rative for all microbiologists around the world, since the biological weapons are a threat for the human life.
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9 Lee mas

Unprecedented plant species loss after a decade in fragmented subtropical Chaco Serrano forests.

Unprecedented plant species loss after a decade in fragmented subtropical Chaco Serrano forests.

whether the amount of forest cover decreased or increased, respectively. In contrast, small for- est fragments showed a relatively constant proportion of species lost (~25%) regardless of either forest cover increased or decreased in their surroundings. These results suggest an over- all degradation in habitat quality within small forest remnants and in their surrounding buffer areas. In other words, there is such a low proportion of forest cover left surrounding these small forest fragments that the changes observed do not appear to have any impact on their connectivity. Notice that in the case of larger forest remnants (> 10.7ha), the circular buffer areas of 250m and 500m imply that at least part of the changes in forest cover (shrub and tree cover) is taking place within them. Hence, while the area of these forest fragments remained as in 2003, there was an impoverishment of high vegetation cover at local and regional levels across this time period. In this regard, there are two important anthropogenic drivers that may be affecting habitat quality within the studied forest remnants and in the surrounding buffer areas. Cattle production is generally in a relatively low-density but there are literally no single cattle-free forest remnants within the studied region [16, 35, 50, 51]. Grazing and trampling by domestic cattle can seriously affect the growth and recruitment of most plant species, as it has been observed in the studied region [50, 51]. Secondly, the Chaco Serrano presents the highest numbers of fire events, burned area, and fire frequency in central Argentina over the past 18 years [52], which are mainly caused by humans due to negligent ignitions for cattle pasture management [52, 53]. We argue that both of these anthropogenic drivers have probably had stronger influence in the forest cover of larger than smaller forest remnants due to their tradi- tional different land uses. While most of the smaller forest fragments studied currently remains embedded in highly modified agricultural matrices, the larger forest fragments are mostly sub- jected to cattle production, which in turn are also more frequently burnt [52, 53]. These differ- ent land uses may help explain the forest cover patterns changes observed across the studied forest remnants after a decade and therefore help to understand their similar species loss across the fragmentation-size gradient.
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16 Lee mas

Hydraulic behaviour of bentonite based mixtures in engineered barriers: The Backfill and Plug Test at the Äspö HRL (Sweden)

Hydraulic behaviour of bentonite based mixtures in engineered barriers: The Backfill and Plug Test at the Äspö HRL (Sweden)

In order to find out the influence of pore fluid on the micro and macrostructural levels, four MIP tests were performed in compacted specimens of a mixture of sodium bentonite (B) and sand (S) with B/S = 70/30 (by mass) used to study the total suction at two dry specific weights and two salt concentration on water used to saturate them (Mata et al. 2002). Soil specimens were wetted with salt and distilled water, after the specimens were compacted at 16.7 kN/m 3 and 13.7 kN/m 3 and finally, air-dried in a room where relative humidity was 47% at free shrinkage conditions. Dry specific weight was not controlled after the drying process. Soil structure was then studied by means of porosimetry tests at the corresponding water content at this relative humidity. Soil specimens were not freeze-dried after the drying process in this controlled relative humidity room. Therefore, water content at the microstructural level might be high enough to prevent mercury intrusion affecting the results at this structural level. From the results two main features were observed: no microstructure differences were observed and macrostructure differences were measured after the MIP tests. MIP test results are depicted in figures 3.20 and 3.21 at both dry specific weights. It is interesting to note that at both dry specific weights and independently on water salinity, the predominant pore size in the microstructure was the same for the four specimens (0.017 µm) and the incremental intruded pore volume was also the same (around 105 mL/kg). However, specimens hydrated and saturated with salt water presented higher incremental intruded pore volume than those saturated with distilled water. From these results could be concluded that salt water effects were significant on the macropores and not important on the micropores. In addition to that, changes in dry specific weight of the specimens only induced changes in the volume of mercury intruded at the macrostructure level. The results obtained by Acar & Olivieri (1989) were similar when MIP tests were performed in compacted kaolinite specimens at different energy levels (specimens were freeze-dried) and no changes in the smaller mode were observed.
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280 Lee mas

Nitrogen carbon graphite like semiconductor synthesized from uric acid

Nitrogen carbon graphite like semiconductor synthesized from uric acid

electronic band structure calculated using MOPAC, depicted in Fig.. direct band gap at the edge of the Brillouin zone.[r]

41 Lee mas

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