6,281 research outputs found
Understanding Greenhouse Gases
Students will conduct hands-on experiments to see how greenhouse gases interact with the Earth’s atmosphere and how greenhouse gases affect temperature. This lesson introduces National Geographic’s Geo-Inquiry Process, where students will identify a Geo-inquiry question, collect data, and create a project around the answer to their question. Students will then present their findings to their peers and evaluate their Geo-Inquiry process
Co-infection of the four major Plasmodium species: effects on densities and gametocyte carriage
BACKGROUND: Co-infection of the four major species of human malaria parasite Plasmodium falciparum (Pf), P. vivax (Pv), P. malariae (Pm), and P. ovale sp. (Po) is regularly observed, but there is limited understanding of between-species interactions. In particular, little is known about the effects of multiple Plasmodium species co-infections on gametocyte production. METHODS: We developed molecular assays for detecting asexual and gametocyte stages of Pf, Pv, Pm, and Po. This is the first description of molecular diagnostics for Pm and Po gametocytes. These assays were implemented in a unique epidemiological setting in Papua New Guinea with sympatric transmission of all four Plasmodium species permitting a comprehensive investigation of species interactions. FINDINGS: The observed frequency of Pf-Pv co-infection for asexual parasites (14.7%) was higher than expected from individual prevalence rates (23.8%Pf x 47.4%Pv = 11.3%). The observed frequency of co-infection with Pf and Pv gametocytes (4.6%) was higher than expected from individual prevalence rates (13.1%Pf x 28.2%Pv = 3.7%). The excess risk of co-infection was 1.38 (95% confidence interval (CI): 1.09, 1.67) for all parasites and 1.37 (95% CI: 0.95, 1.79) for gametocytes. This excess co-infection risk was partially attributable to malaria infections clustering in some villages. Pf-Pv-Pm triple infections were four times more frequent than expected by chance alone, which could not be fully explained by infections clustering in highly exposed individuals. The effect of co-infection on parasite density was analyzed by systematic comparison of all pairwise interactions. This revealed a significant 6.57-fold increase of Pm density when co-infected with Pf. Pm gametocytemia also increased with Pf co-infection. CONCLUSIONS: Heterogeneity in exposure to mosquitoes is a key epidemiological driver of Plasmodium co-infection. Among the four co-circulating parasites, Pm benefitted most from co-infection with other species. Beyond this, no general prevailing pattern of suppression or facilitation was identified in pairwise analysis of gametocytemia and parasitemia of the four species. TRIAL REGISTRATION: This trial is registered with ClinicalTrials.gov, Trial ID: NCT02143934
Plasmodium vivax and Plasmodium falciparum infection dynamics: re-infections, recrudescences and relapses
Background: In malaria endemic populations, complex patterns of Plasmodium vivax and Plasmodium falciparum blood-stage infection dynamics may be observed. Genotyping samples from longitudinal cohort studies for merozoite surface protein (msp) variants increases the information available in the data, allowing multiple infecting parasite clones in a single individual to be identified. msp genotyped samples from two longitudinal cohorts in Papua New Guinea (PNG) and Thailand were analysed using a statistical model where the times of acquisition and clearance of each clone in every individual were estimated using a process of data augmentation. Results: For the populations analysed, the duration of blood-stage P. falciparum infection was estimated as 36 (95% Credible Interval (CrI): 29, 44) days in PNG, and 135 (95% CrI 94, 191) days in Thailand. Experiments on simulated data indicated that it was not possible to accurately estimate the duration of blood-stage P. vivax infections due to the lack of identifiability between a single blood-stage infection and multiple, sequential blood-stage infections caused by relapses. Despite this limitation, the method and data point towards short duration of blood-stage P. vivax infection with a lower bound of 24 days in PNG, and 29 days in Thailand. On an individual level, P. vivax recurrences cannot be definitively classified into re-infections, recrudescences or relapses, but a probabilistic relapse phenotype can be assigned to each P. vivax sample, allowing investigation of the association between epidemiological covariates and the incidence of relapses. Conclusion: The statistical model developed here provides a useful new tool for in-depth analysis of malaria data from longitudinal cohort studies, and future application to data sets with multi-locus genotyping will allow more detailed investigation of infection dynamics
Assessment of historical changes (1959–2012) and the causes of recent break-ups of the Petersen ice shelf, Nunavut, Canada
Wide-angle elastic scattering and color randomization
Baryon-baryon elastic scattering is considered in the independent scattering
(Landshoff) mechanism. It is suggested that for scattering at moderate
energies, direct and interchange quark channels contribute with equal color
coefficients because the quark color is randomized by soft gluon exchange
during the hadronization stage. With this assumption, it is shown that the
ratio of cross sections at CM angle
decreases from a high energy value of R_{\pbar p / pp} \approx 1/2.7, down to
R_{\pbar p / pp} \approx 1/28, compatible with experimental data at moderate
energies. This sizable fall in the ratio seems to be characteristic of the
Landshoff mechanism, in which changes at the quark level have a strong effect
precisely because the hadronic process occurs via multiple quark scatterings.
The effect of color randomization on the angular distribution of proton-proton
elastic scattering and the cross section ratio is also discussed.Comment: 18 pages, latex2e, 4 uuencoded figures, include
An Infrared through Radio Study of the Properties and Evolution of IRDC Clumps
We examine the physical properties and evolutionary stages of a sample of 17
clumps within 8 Infrared Dark Clouds (IRDCs) by combining existing infrared,
millimeter, and radio data with new Bolocam Galactic Plane Survey (BGPS) 1.1 mm
data, VLA radio continuum data, and HHT dense gas (HCO+ and N2H+) spectroscopic
data. We combine literature studies of star formation tracers and dust
temperatures within IRDCs with our search for ultra-compact (UC) HII regions to
discuss a possible evolutionary sequence for IRDC clumps. In addition, we
perform an analysis of mass tracers in IRDCs and find that 8 micron extinction
masses and 1.1 mm Bolocam Galactic Plane Survey (BGPS) masses are complementary
mass tracers in IRDCs except for the most active clumps (notably those
containing UCHII regions), for which both mass tracers suffer biases. We find
that the measured virial masses in IRDC clumps are uniformly higher than the
measured dust continuum masses on the scale of ~1 pc. We use 13CO, HCO+, and
N2H+ to study the molecular gas properties of IRDCs and do not see any evidence
of chemical differentiation between hot and cold clumps on the scale of ~1 pc.
However, both HCO+ and N2H+ are brighter in active clumps, due to an increase
in temperature and/or density. We report the identification of four UCHII
regions embedded within IRDC clumps and find that UCHII regions are associated
with bright (>1 Jy) 24 micron point sources, and that the brightest UCHII
regions are associated with "diffuse red clumps" (an extended enhancement at 8
micron). The broad stages of the discussed evolutionary sequence (from a
quiescent clump to an embedded HII region) are supported by literature dust
temperature estimates; however, no sequential nature can be inferred between
the individual star formation tracers.Comment: 33 pages, 26 figures, 6 tables, accepted for publication in ApJ. Full
resolution version available here:
http://casa.colorado.edu/~battersb/Publications.htm
Next-to-leading and resummed BFKL evolution with saturation boundary
We investigate the effects of the saturation boundary on small-x evolution at
the next-to-leading order accuracy and beyond. We demonstrate that the
instabilities of the next-to-leading order BFKL evolution are not cured by the
presence of the nonlinear saturation effects, and a resummation of the higher
order corrections is therefore needed for the nonlinear evolution. The
renormalization group improved resummed equation in the presence of the
saturation boundary is investigated, and the corresponding saturation scale is
extracted. A significant reduction of the saturation scale is found, and we
observe that the onset of the saturation corrections is delayed to higher
rapidities. This seems to be related to the characteristic feature of the
resummed splitting function which at moderately small values of x possesses a
minimum.Comment: 34 page
Theoretical issues of small physics
The perturbative QCD predictions concerning deep inelastic scattering at low
are summarized. The theoretical framework based on the leading log
resummation and factorization theorem is described and some recent
developments concerning the BFKL equation and its generalization are discussed.
The QCD expectations concerning the small behaviour of the spin dependent
structure function are briefly summarized and the importance of
the double logarithmic terms which sum contributions containing the leading
powers of is emphasised. The role of studying final states
in deep inelastic scattering for revealing the details of the underlying
dynamics at low is pointed out and some dedicated measurements, like deep
inelastic scattering accompanied by an energetic jet, the measurement of the
transverse energy flow etc., are briefly discussed.Comment: 17 pages, LATEX, 7 uuencoded eps figures include
Asymptomatic Plasmodium vivax infections induce robust IgG responses to multiple blood-stage proteins in a low-transmission region of western Thailand
BACKGROUND: Thailand is aiming to eliminate malaria by the year
2024. Plasmodium vivax has now become the dominant species
causing malaria within the country, and a high proportion of
infections are asymptomatic. A better understanding of antibody
dynamics to P. vivax antigens in a low-transmission setting,
where acquired immune responses are poorly characterized, will
be pivotal for developing new strategies for elimination, such
as improved surveillance methods and vaccines. The objective of
this study was to characterize total IgG antibody levels to 11
key P. vivax proteins in a village of western Thailand. METHODS:
Plasma samples from 546 volunteers enrolled in a cross-sectional
survey conducted in 2012 in Kanchanaburi Province were utilized.
Total IgG levels to 11 different proteins known or predicted to
be involved in reticulocyte binding or invasion (ARP, GAMA, P41,
P12, PVX_081550, and five members of the PvRBP family), as well
as the leading pre-erythrocytic vaccine candidate (CSP) were
measured using a multiplexed bead-based assay. Associations
between IgG levels and infection status, age, and spatial
location were explored. RESULTS: Individuals from a
low-transmission region of western Thailand reacted to all 11 P.
vivax recombinant proteins. Significantly greater IgG levels
were observed in the presence of a current P. vivax infection,
despite all infected individuals being asymptomatic. IgG levels
were also higher in adults (18 years and older) than in
children. For most of the proteins, higher IgG levels were
observed in individuals living closer to the Myanmar border and
further away from local health services. CONCLUSIONS: Robust IgG
responses were observed to most proteins and IgG levels
correlated with surrogates of exposure, suggesting these
antigens may serve as potential biomarkers of exposure,
immunity, or both
DHODH modulates transcriptional elongation in the neural crest and melanoma
Melanoma is a tumour of transformed melanocytes, which are originally derived from the embryonic neural crest. It is unknown to what extent the programs that regulate neural crest development interact with mutations in the BRAF oncogene, which is the most commonly mutated gene in human melanoma1. We have used zebrafish embryos to identify the initiating transcriptional events that occur on activation of human BRAF(V600E) (which encodes an amino acid substitution mutant of BRAF) in the neural crest lineage. Zebrafish embryos that are transgenic for mitfa:BRAF(V600E) and lack p53 (also known as tp53) have a gene signature that is enriched for markers of multipotent neural crest cells, and neural crest progenitors from these embryos fail to terminally differentiate. To determine whether these early transcriptional events are important for melanoma pathogenesis, we performed a chemical genetic screen to identify small-molecule suppressors of the neural crest lineage, which were then tested for their effects on melanoma. One class of compound, inhibitors of dihydroorotate dehydrogenase (DHODH), for example leflunomide, led to an almost complete abrogation of neural crest development in zebrafish and to a reduction in the self-renewal of mammalian neural crest stem cells. Leflunomide exerts these effects by inhibiting the transcriptional elongation of genes that are required for neural crest development and melanoma growth. When used alone or in combination with a specific inhibitor of the BRAF(V600E) oncogene, DHODH inhibition led to a marked decrease in melanoma growth both in vitro and in mouse xenograft studies. Taken together, these studies highlight developmental pathways in neural crest cells that have a direct bearing on melanoma formation
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