716 research outputs found
The Growth Response of Two Diatom Species to Atmospheric Dust from the Last Glacial Maximum
Relief of iron (Fe) limitation in the surface Southern Ocean has been suggested as one driver of the regular glacial-interglacial cycles in atmospheric carbon dioxide (CO). The proposed cause is enhanced deposition of Fe-bearing atmospheric dust to the oceans during glacial intervals, with consequent effects on export production and the carbon cycle. However, understanding the role of enhanced atmospheric Fe supply in biogeochemical cycles is limited by knowledge of the fluxes and 'bioavailability' of atmospheric Fe during glacial intervals. Here, we assess the effect of Fe fertilization by dust, dry-extracted from the Last Glacial Maximum portion of the EPICA Dome C Antarctic ice core, on the Antarctic diatom species and . Both species showed strong but differing reactions to dust addition. increased cell number (3880 vs.786 cells mL), chlorophyll a (51 vs. 3.9 μg mL) and particulate organic carbon (POC; 1.68 vs. 0.28 μg mL) production in response to dust compared to controls. did not increase cell number in response to dust, but chlorophyll and POC per cell both strongly increased compared to controls (39 vs. 15 and 2.13 vs. 0.95 ng cell respectively). The net result of both responses was a greater production of POC and chlorophyll , as well as decreased Si:C and Si:N incorporation ratios within cells. However, decreased silicate uptake for the same nitrate and carbon uptake, while increased carbon and nitrate uptake for the same silicate uptake. This suggests that nutrient utilization changes in response to Fe addition could be driven by different underlying mechanisms between different diatom species. Enhanced supply of atmospheric dust to the surface ocean during glacial intervals could therefore have driven nutrient-utilization changes which could permit greater carbon fixation for lower silica utilization. Additionally, both species responded more strongly to lower amounts of direct Fe chloride addition than they did to dust, suggesting that not all the Fe released from dust was in a bioavailable form available for uptake by diatoms.Natural Environment Research Council (Studentship), Royal Society (Grant ID: RP120096), German Research Foundation (Grant IDs: HO-4217, BR-3794
Lattice QCD at the physical point: Simulation and analysis details
We give details of our precise determination of the light quark masses
m_{ud}=(m_u+m_d)/2 and m_s in 2+1 flavor QCD, with simulated pion masses down
to 120 MeV, at five lattice spacings, and in large volumes. The details concern
the action and algorithm employed, the HMC force with HEX smeared clover
fermions, the choice of the scale setting procedure and of the input masses.
After an overview of the simulation parameters, extensive checks of algorithmic
stability, autocorrelation and (practical) ergodicity are reported. To
corroborate the good scaling properties of our action, explicit tests of the
scaling of hadron masses in N_f=3 QCD are carried out. Details of how we
control finite volume effects through dedicated finite volume scaling runs are
reported. To check consistency with SU(2) Chiral Perturbation Theory the
behavior of M_\pi^2/m_{ud} and F_\pi as a function of m_{ud} is investigated.
Details of how we use the RI/MOM procedure with a separate continuum limit of
the running of the scalar density R_S(\mu,\mu') are given. This procedure is
shown to reproduce the known value of r_0m_s in quenched QCD. Input from
dispersion theory is used to split our value of m_{ud} into separate values of
m_u and m_d. Finally, our procedure to quantify both systematic and statistical
uncertainties is discussed.Comment: 45 page
Gross-Neveu Models, Nonlinear Dirac Equations, Surfaces and Strings
Recent studies of the thermodynamic phase diagrams of the Gross-Neveu model
(GN2), and its chiral cousin, the NJL2 model, have shown that there are phases
with inhomogeneous crystalline condensates. These (static) condensates can be
found analytically because the relevant Hartree-Fock and gap equations can be
reduced to the nonlinear Schr\"odinger equation, whose deformations are
governed by the mKdV and AKNS integrable hierarchies, respectively. Recently,
Thies et al have shown that time-dependent Hartree-Fock solutions describing
baryon scattering in the massless GN2 model satisfy the Sinh-Gordon equation,
and can be mapped directly to classical string solutions in AdS3. Here we
propose a geometric perspective for this result, based on the generalized
Weierstrass spinor representation for the embedding of 2d surfaces into 3d
spaces, which explains why these well-known integrable systems underlie these
various Gross-Neveu gap equations, and why there should be a connection to
classical string theory solutions. This geometric viewpoint may be useful for
higher dimensional models, where the relevant integrable hierarchies include
the Davey-Stewartson and Novikov-Veselov systems.Comment: 27 pages, 1 figur
Abnormal IgD and IgA1 O-glycosylation in hyperimmunoglobulinaemia D and periodic fever syndrome
In order to determine the glycosylation pattern for IgD, and to examine whether there are changes in the pattern of IgD and IgA1 O-glycosylation in patients with hyperimmunoglobulinaemia D and periodic fever syndrome (HIDS) during acute febrile attacks and during periods of quiescence, serum was obtained from 20 patients with HIDS and 20 control subjects. In the HIDS group, serum was obtained either during an acute febrile episode (n = 9) or during a period of quiescence (n = 11). The O-glycosylation profiles of native and desialylated IgA1 and IgD were measured in an ELISA-type system using the lectins Helix aspersa and peanut agglutinin, which bind to alternative forms of O-glycan moieties. IgD is more heavily O-galactosylated and less O-sialylated than IgA1 in healthy subjects. HIDS is associated with more extensive O-galactosylation of IgD and a reduction in O-sialylation of both IgD and IgA1. These changes are present both during acute febrile attacks and periods of quiescence. The T cell IgD receptor is a lectin with binding affinity for the O-glycans of both IgD and IgA1. The observed changes in IgD and IgA1 O-glycosylation are likely to have a significant effect on IgD/IgA1–T cell IgD receptor interactions including basal immunoglobulin synthesis, and possibly myeloid IgD receptor-mediated cytokine release
Thyroid-Disrupting Chemicals: Interpreting Upstream Biomarkers of Adverse Outcomes
Background There is increasing evidence in humans and in experimental animals for a relationship between exposure to specific environmental chemicals and perturbations in levels of critically important thyroid hormones (THs). Identification and proper interpretation of these relationships are required for accurate assessment of risk to public health. Objectives We review the role of TH in nervous system development and specific outcomes in adults, the impact of xenobiotics on thyroid signaling, the relationship between adverse outcomes of thyroid disruption and upstream causal biomarkers, and the societal implications of perturbations in thyroid signaling by xenobiotic chemicals. Data sources We drew on an extensive body of epidemiologic, toxicologic, and mechanistic studies. Data synthesis THs are critical for normal nervous system development, and decreased maternal TH levels are associated with adverse neuropsychological development in children. In adult humans, increased thyroid-stimulating hormone is associated with increased blood pressure and poorer blood lipid profiles, both risk factors for cardiovascular disease and death. These effects of thyroid suppression are observed even within the “normal” range for the population. Environmental chemicals may affect thyroid homeostasis by a number of mechanisms, and multiple chemicals have been identified that interfere with thyroid function by each of the identified mechanisms. Conclusions Individuals are potentially vulnerable to adverse effects as a consequence of exposure to thyroid-disrupting chemicals. Any degree of thyroid disruption that affects TH levels on a population basis should be considered a biomarker of adverse outcomes, which may have important societal outcomes
Asteroseismology and Interferometry
Asteroseismology provides us with a unique opportunity to improve our
understanding of stellar structure and evolution. Recent developments,
including the first systematic studies of solar-like pulsators, have boosted
the impact of this field of research within Astrophysics and have led to a
significant increase in the size of the research community. In the present
paper we start by reviewing the basic observational and theoretical properties
of classical and solar-like pulsators and present results from some of the most
recent and outstanding studies of these stars. We centre our review on those
classes of pulsators for which interferometric studies are expected to provide
a significant input. We discuss current limitations to asteroseismic studies,
including difficulties in mode identification and in the accurate determination
of global parameters of pulsating stars, and, after a brief review of those
aspects of interferometry that are most relevant in this context, anticipate
how interferometric observations may contribute to overcome these limitations.
Moreover, we present results of recent pilot studies of pulsating stars
involving both asteroseismic and interferometric constraints and look into the
future, summarizing ongoing efforts concerning the development of future
instruments and satellite missions which are expected to have an impact in this
field of research.Comment: Version as published in The Astronomy and Astrophysics Review, Volume
14, Issue 3-4, pp. 217-36
PCB-containing wood floor finish is a likely source of elevated PCBs in residents' blood, household air and dust: a case study of exposure
© 2008 Rudel et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution Licens
The quest for the solar g modes
Solar gravity modes (or g modes) -- oscillations of the solar interior for
which buoyancy acts as the restoring force -- have the potential to provide
unprecedented inference on the structure and dynamics of the solar core,
inference that is not possible with the well observed acoustic modes (or p
modes). The high amplitude of the g-mode eigenfunctions in the core and the
evanesence of the modes in the convection zone make the modes particularly
sensitive to the physical and dynamical conditions in the core. Owing to the
existence of the convection zone, the g modes have very low amplitudes at
photospheric levels, which makes the modes extremely hard to detect. In this
paper, we review the current state of play regarding attempts to detect g
modes. We review the theory of g modes, including theoretical estimation of the
g-mode frequencies, amplitudes and damping rates. Then we go on to discuss the
techniques that have been used to try to detect g modes. We review results in
the literature, and finish by looking to the future, and the potential advances
that can be made -- from both data and data-analysis perspectives -- to give
unambiguous detections of individual g modes. The review ends by concluding
that, at the time of writing, there is indeed a consensus amongst the authors
that there is currently no undisputed detection of solar g modes.Comment: 71 pages, 18 figures, accepted by Astronomy and Astrophysics Revie
Phylogenetic analysis of metastatic progression in breast cancer using somatic mutations and copy number aberrations.
Several studies using genome-wide molecular techniques have reported various degrees of genetic heterogeneity between primary tumours and their distant metastases. However, it has been difficult to discern patterns of dissemination owing to the limited number of patients and available metastases. Here, we use phylogenetic techniques on data generated using whole-exome sequencing and copy number profiling of primary and multiple-matched metastatic tumours from ten autopsied patients to infer the evolutionary history of breast cancer progression. We observed two modes of disease progression. In some patients, all distant metastases cluster on a branch separate from their primary lesion. Clonal frequency analyses of somatic mutations show that the metastases have a monoclonal origin and descend from a common 'metastatic precursor'. Alternatively, multiple metastatic lesions are seeded from different clones present within the primary tumour. We further show that a metastasis can be horizontally cross-seeded. These findings provide insights into breast cancer dissemination
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