Atlantic Forcing of Persistent Drought in West Africa Shanahan, T.M; Overpeck, J.T; Anchukaitis, K.J ...
Science (American Association for the Advancement of Science),
04/2009, Letnik:
324, Številka:
5925
Journal Article
Recenzirano
Although persistent drought in West Africa is well documented from the instrumental record and has been primarily attributed to changing Atlantic sea surface temperatures, little is known about the ...length, severity, and origin of drought before the 20th century. We combined geomorphic, isotopic, and geochemical evidence from the sediments of Lake Bosumtwi, Ghana, to reconstruct natural variability in the African monsoon over the past three millennia. We find that intervals of severe drought lasting for periods ranging from decades to centuries are characteristic of the monsoon and are linked to natural variations in Atlantic temperatures. Thus the severe drought of recent decades is not anomalous in the context of the past three millennia, indicating that the monsoon is capable of longer and more severe future droughts.
The La Niña and El Niño phases of the El Niño-Southern Oscillation (ENSO) have major impacts on regional rainfall patterns around the globe, with substantial environmental, societal and economic ...implications. Long-term perspectives on ENSO behaviour, under changing background conditions, are essential to anticipating how ENSO phases may respond under future climate scenarios. Here, we derive a 7700-year, quantitative precipitation record using carbon isotope ratios from a single species of leaf preserved in lake sediments from subtropical eastern Australia. We find a generally wet (more La Niña-like) mid-Holocene that shifted towards drier and more variable climates after 3200 cal. yr BP, primarily driven by increasing frequency and strength of the El Niño phase. Climate model simulations implicate a progressive orbitally-driven weakening of the Pacific Walker Circulation as contributing to this change. At centennial scales, high rainfall characterised the Little Ice Age (~1450-1850 CE) in subtropical eastern Australia, contrasting with oceanic proxies that suggest El Niño-like conditions prevail during this period. Our data provide a new western Pacific perspective on Holocene ENSO variability and highlight the need to address ENSO reconstruction with a geographically diverse network of sites to characterise how both ENSO, and its impacts, vary in a changing climate.
We use deep HST/ACS observations to calculate the star formation history (SFH) of the Cetus dwarf spheroidal (dSph) galaxy. Our photometry reaches below the oldest main-sequence turnoffs, which ...allows us to estimate the age and duration of the main episode of star formation in Cetus. This is well approximated by a single episode that peaked roughly 12 {+-} 0.5 Gyr ago and lasted no longer than about 1.9 {+-} 0.5 Gyr (FWHM). Our solution also suggests that essentially no stars formed in Cetus during the past 8 Gyr. This makes Cetus' SFH comparable to that of the oldest Milky Way dSphs. Given the current isolation of Cetus in the outer fringes of the Local Group, the dominant old population implies that Cetus is a clear outlier in the morphology-Galactocentric distance relation that holds for the majority of the Milky Way dwarf satellites. Our results also show that Cetus continued forming stars until z{approx_equal} 1, long after the universe was reionized, and that there is no clear signature of the epoch of reionization in Cetus' SFH. We briefly discuss the implications of these results for dwarf galaxy evolution models. Finally, we present a comprehensive account of the data reduction and analysis strategy adopted for all galaxies targeted by the LCID (Local Cosmology from Isolated Dwarfs) project. We employ two different photometry codes (DAOPHOT/ALLFRAME and DOLPHOT), three different SFH reconstruction codes (IAC-pop/MinnIAC, MATCH, and COLE), and two stellar evolution libraries (BaSTI and Padova/Girardi), allowing for a detailed assessment of the modeling and observational uncertainties.
For several decades, breeding goals in dairy cattle focussed on increased milk production. However, many functional traits have negative genetic correlations with milk yield, and reductions in ...genetic merit for health and fitness have been observed. Herd management has been challenged to compensate for these effects and to balance fertility, udder health and metabolic diseases against increased production to maximize profit without compromising welfare. Functional traits, such as direct information on cow health, have also become more important because of growing concern about animal well-being and consumer demands for healthy and natural products. There are major concerns about the impact of drugs used in veterinary medicine on the spread of antibiotic-resistant strains of bacteria that can negatively impact human health. Sustainability and efficiency are also increasingly important because of the growing competition for high-quality, plant-based sources of energy and protein. Disruptions to global environments because of climate change may encourage yet more emphasis on these traits. To be successful, it is vital that there be a balance between the effort required for data recording and subsequent benefits. The motivation of farmers and other stakeholders involved in documentation and recording is essential to ensure good data quality. To keep labour costs reasonable, existing data sources should be used as much as possible. Examples include the use of milk composition data to provide additional information about the metabolic status or energy balance of the animals. Recent advances in the use of mid-infrared spectroscopy to measure milk have shown considerable promise, and may provide cost-effective alternative phenotypes for difficult or expensive-to-measure traits, such as feed efficiency. There are other valuable data sources in countries that have compulsory documentation of veterinary treatments and drug use. Additional sources of data outside of the farm include, for example, slaughter houses (meat composition and quality) and veterinary labs (specific pathogens, viral loads). At the farm level, many data are available from automated and semi-automated milking and management systems. Electronic devices measuring physiological status or activity parameters can be used to predict events such as oestrus, and also behavioural traits. Challenges concerning the predictive biology of indicator traits or standardization need to be solved. To develop effective selection programmes for new traits, the development of large databases is necessary so that high-reliability breeding values can be estimated. For expensive-to-record traits, extensive phenotyping in combination with genotyping of females is a possibility.
It is well-known that there is considerable variation in the effectiveness of evidence-based treatments for psychiatric disorders, and a continued need to improve the real-world effectiveness of ...these treatments. In the last 20+ years the examination of noninvasive brain stimulation techniques for psychiatric treatment has increased dramatically. However, in order to test these techniques for effective therapeutic use, it is critical to understand (a) (what are) the key neural circuits to engage for specific disorders or clusters of symptoms, and (b) (how) can these circuits be reached effectively using neurostimulation? Here we focus on the research toward the application of transcranial direct current stimulation (tDCS) for posttraumatic stress disorder (PTSD). tDCS is a portable and inexpensive technique that lends itself well to be combined with, and thus potentially augment, exposure-based treatment for PTSD. In this review, we discuss the behavioral model of threat and safety learning and memory as it relates to PTSD, the underlying neurobiology of PTSD, as well as the current understandings of tDCS action, including its limitations and opportunities. Through this lens, we summarize the research on the application of tDCS to modulated threat and safety learning and memory to date, and propose new directions for its future research.
The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic has made it clear that combating coronavirus outbreaks benefits from a combination of vaccines and therapeutics. A promising ...drug target common to all coronaviruses-including SARS-CoV, MERS-CoV, and SARS-CoV-2-is the papain-like protease (PLpro). PLpro cleaves part of the viral replicase polyproteins into non-structural protein subunits, which are essential to the viral replication cycle. Additionally, PLpro can cleave both ubiquitin and the ubiquitin-like protein ISG15 from host cell substrates as a mechanism to evade innate immune responses during infection. These roles make PLpro an attractive antiviral drug target. Here we demonstrate that ubiquitin variants (UbVs) can be selected from a phage-displayed library and used to specifically and potently block SARS-CoV-2 PLpro activity. A crystal structure of SARS-CoV-2 PLpro in complex with a representative UbV reveals a dimeric UbV bound to PLpro at a site distal to the catalytic site. Yet, the UbV inhibits the essential cleavage activities of the protease in vitro and in cells, and it reduces viral replication in cell culture by almost five orders of magnitude.
Although disrupted in schizophrenia 1 (DISC1) has been implicated in many psychiatric disorders, including schizophrenia, bipolar disorder, schizoaffective disorder and major depression, its ...biological role in these disorders is unclear. To better understand this gene and its role in psychiatric disease, we conducted transcriptional profiling and genome-wide association analysis in 1232 pedigreed Mexican-American individuals for whom we have neuroanatomic images, neurocognitive assessments and neuropsychiatric diagnoses. SOLAR was used to determine heritability, identify gene expression patterns and perform association analyses on 188 quantitative brain-related phenotypes. We found that the DISC1 transcript is highly heritable (h(2)=0.50; P=1.97 × 10(-22)), and that gene expression is strongly cis-regulated (cis-LOD=3.89) but is also influenced by trans-effects. We identified several DISC1 polymorphisms that were associated with cortical gray matter thickness within the parietal, temporal and frontal lobes. Associated regions affiliated with memory included the entorhinal cortex (rs821639, P=4.11 × 10(-5); rs2356606, P=4.71 × 10(-4)), cingulate cortex (rs16856322, P=2.88 × 10(-4)) and parahippocampal gyrus (rs821639, P=4.95 × 10(-4)); those affiliated with executive and other cognitive processing included the transverse temporal gyrus (rs9661837, P=5.21 × 10(-4); rs17773946, P=6.23 × 10(-4)), anterior cingulate cortex (rs2487453, P=4.79 × 10(-4); rs3738401, P=5.43 × 10(-4)) and medial orbitofrontal cortex (rs9661837; P=7.40 × 10(-4)). Cognitive measures of working memory (rs2793094, P=3.38 × 10(-4)), as well as lifetime history of depression (rs4658966, P=4.33 × 10(-4); rs12137417, P=4.93 × 10(-4)) and panic (rs12137417, P=7.41 × 10(-4)) were associated with DISC1 sequence variation. DISC1 has well-defined genetic regulation and clearly influences important phenotypes related to psychiatric disease.
The Dana-Farber Cancer Institute (DFCI) acute lymphoblastic leukemia (ALL) Consortium has been conducting multi-institutional clinical trials in childhood ALL since 1981. The treatment backbone has ...included 20-30 consecutive weeks of asparaginase during intensification and frequent vincristine/corticosteroid pulses during the continuation phase. Between 1985 and 2000, 1457 children aged 0-18 years were treated on four consecutive protocols: 85-01 (1985-1987), 87-01 (1987-1991), 91-01 (1991-1955) and 95-01 (1996-2000). The 10-year event-free survival (EFS)+/-s.e. by protocol was 77.9+/-2.8% (85-01), 74.2+/-2.3% (87-01), 80.8+/-2.1% (91-01) and 80.5+/-1.8% (95-01). Approximately 82% of patients treated in the 1980s and 88% treated in the 1990s were long-term survivors. Both EFS and overall survival (OS) rates were significantly higher for patients treated in the 1990s compared with the 1980s (P=0.05 and 0.01, respectively). On the two protocols conducted in the 1990s, EFS was 79-85% for T-cell ALL patients and 75-78% for adolescents (age 10-18 years). Results of randomized studies revealed that dexrazoxane prevented acute cardiac injury without adversely affecting EFS or OS in high-risk (HR) patients, and frequently dosed intrathecal chemotherapy was an effective substitute for cranial radiation in standard-risk (SR) patients. Current studies continue to focus on improving efficacy while minimizing acute and late toxicities.
Natural and social systems worldwide are impacted by climate modes such as the El Niño/Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO) and Atlantic Multidecadal Oscillation (AMO), ...making it imperative to understand their sensitivity to climate change. Paleoclimate studies extend the observational climate baseline, and speleothem records (δ18Ospel) are a common data source. However, relationships between δ18Ospel and climate modes are uncertain; climate models provide a way to test the strength and stability of these relationships. Here, we use the isotope‐enabled Community Earth System Model's Last Millennium Ensemble combined with a forward proxy model to delineate the global expression of modal variability in “pseudo‐stalagmite” (δ18Ospel) records worldwide. The modeled δ18Ospel spatially correlates with modal signatures. However, substantial changes in modal variance only modestly affect individual δ18Ospel variance. A network of δ18Ospel records, particularly one that straddles the Pacific, significantly improves the reconstructability of ENSO variance.
Plain Language Summary
Climate variability on interannual‐decadal timescales often takes the form of coherent patterns (“modes”), such as the El Niño/Southern Oscillation (ENSO) phenomenon of the tropical Pacific. These patterns strongly impact global climate, and how they will change as the world warms remains uncertain. Although instrumental climate records are relatively short, paleoclimate records reveal past changes in these modes, allowing us to document their ranges of natural variability. A common approach is to use records of oxygen isotopic variations preserved in, for example, cave formations. To interpret these data, we must understand how climate modes impact the local isotopic content of precipitation and account for how paleoclimate data record this signal. Here, we use a climate model that includes isotope physics in the hydrologic cycle to show that although the oxygen isotope record in cave formations is influenced by different climate modes, the magnitude of the signal at any individual site appears relatively small. However, in the model, combining cave records from multiple regions can reconstruct past changes in the strength of ENSO. Multidecadal modes are more challenging to reconstruct from modeled cave records, perhaps reflecting model biases toward too‐weak multidecadal variability and too‐strong ENSO.
Key Points
Coherent δ18O patterns are associated with the El Niño Southern Oscillation/Pacific Decadal Oscillation/Atlantic Multidecadal Oscillation
Changes in the strength of major climate modes lead to relatively small changes in the speleothem δ18O variability at individual sites
Using a well‐distributed network of speleothem δ18O greatly increases the fidelity of modal variance reconstructions
•The effect of feed concentration on RFC flotation performance was investigated.•Recovery was strongly linked to the gas and hydrophobic solids fluxes.•Estimates of the bubble surface coverage ranged ...from 6% to 18%.•Recovery decreased as bubble surface coverage increased.•Strong concentrate desliming was observed over a 16-fold increase in feed concentration.
This study examines the separation performance achieved using the Reflux Flotation Cell (RFC) when treating low economic value coal waste streams over a range of feed solids concentrations. Feed solids concentrations of 1.3, 2.4 and 5.7 wt% were examined using a fine coal suspension of nominally 50 wt% head ash, covering the typical range emerging from the overflow of a desliming hydrocyclone. This work was also extended to include much higher levels of ultrafine gangue through the addition of significant levels of silica, resulting in an extreme feed ash of 97 wt% head ash, the aim being to assess whether these levels of gangue minerals affect hydrophobic particle capture. For the actual plant feed, as the feed solids concentration was increased the flux of hydrophobic particles fed to the RFC increased in a fixed ratio to the flux of hydrophilic particles. These results showed a greater gas flux was required to maintain combustible recovery as the feed flux of hydrophobic particles increased. The relationship between bubble surface coverage and hydrophobic particle recovery was also investigated. Estimates of the average bubble surface coverages, ranging 6–18%, showed a decreasing trend between recovery and surface coverage. By establishing a strong positive liquid bias flux, ∼0.7 cm/s in magnitude, the product ash was maintained within a narrow band of 7.0–11.9 wt% ash across the series of experiments, demonstrating consistent and strong product desliming over the up to 16-fold increase in feed solids concentration.
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