The elemental composition of the Sun Grevesse, Nicolas; Scott, Pat; Asplund, Martin ...
Astronomy and astrophysics (Berlin),
1/2015, Letnik:
573
Journal Article
Recenzirano
We re-evaluate the abundances of the elements in the Sun from copper (Z = 29) to thorium (Z = 90). Our results are mostly based on neutral and singly-ionised lines in the solar spectrum. We use the ...latest 3D hydrodynamic solar model atmosphere, and in a few cases also correct for departures from local thermodynamic equilibrium (LTE) using non-LTE (NLTE) calculations performed in 1D. In order to minimise statistical and systematic uncertainties, we make stringent line selections, employ the highest-quality observational data and carefully assess oscillator strengths, hyperfine constants and isotopic separations available in the literature, for every line included in our analysis. Our results are typically in good agreement with the abundances in the most pristine meteorites, but there are some interesting exceptions. This analysis constitutes both a full exposition and a slight update of the relevant parts of the preliminary results we presented in Asplund et al. (2009, ARA&A, 47, 481), including full line lists and details of all input data that we have employed.
The elemental composition of the Sun Scott, Pat; Asplund, Martin; Grevesse, Nicolas ...
Astronomy and astrophysics (Berlin),
1/2015, Letnik:
573
Journal Article
Recenzirano
We redetermine the abundances of all iron group nuclei in the Sun, based on neutral and singly-ionised lines of Sc, Ti, V, Mn, Fe, Co and Ni in the solar spectrum. We employ a realistic 3D ...hydrodynamic model solar atmosphere, corrections for departures from local thermodynamic equilibrium (NLTE), stringent line selection procedures and high quality observational data. We have scoured the literature for the best quality oscillator strengths, hyperfine constants and isotopic separations available for our chosen lines. We find log epsilon sub(Sc) = 3.16 + or - 0.04, log epsilon sub(Ti) = 4.93 + or - 0.04, log epsilon sub(V) = 3.89 + or - 0.08, log epsilon sub(Cr) = 5.62 + or - 0.04, log epsilon sub(Mn) = 5.42 + or - 0.04, log epsilon sub(Fe) = 7.47 + or - 0.04, log epsilon sub(Co) = 4.93 + or - 0.05 and log epsilon sub(Ni) = 6.20 + or - 0.04. Our uncertainties factor in both statistical and systematic errors (the latter estimated for possible errors in the model atmospheres and NLTE line formation). The new abundances are generally in good agreement with the CI meteoritic abundances but with some notable exceptions. This analysis constitutes both a full exposition and a slight update of the preliminary results we presented in Asplund et al. (2009, ARA&A, 47, 481), including full line lists and details of all input data we employed.
The elemental composition of the Sun Scott, Pat; Grevesse, Nicolas; Asplund, Martin ...
Astronomy and astrophysics (Berlin),
1/2015, Letnik:
573
Journal Article
Recenzirano
The chemical composition of the Sun is an essential piece of reference data for astronomy, cosmology, astroparticle, space and geo-physics: elemental abundances of essentially all astronomical ...objects are referenced to the solar composition, and basically every process involving the Sun depends on its composition. This article, dealing with the intermediate-mass elements Na to Ca, is the first in a series describing the comprehensive re-determination of the solar composition. In this series we severely scrutinise all ingredients of the analysis across all elements, to obtain the most accurate, homogeneous and reliable results possible. Our results are systematically smaller than most previous ones with the 1D semi-empirical Holweger & Muller model, whereas the 3D model returns abundances very similar to the full 3D calculations. This analysis provides a complete description and a slight update of the results presented in Asplund et al. for Na to Ca, and includes full details of all lines and input data used.
The Chemical Composition of the Sun Asplund, Martin; Grevesse, Nicolas; Sauval, A. Jacques ...
Annual review of astronomy and astrophysics,
01/2009, Letnik:
47, Številka:
1
Journal Article
Recenzirano
Odprti dostop
The solar chemical composition is an important ingredient in our understanding of the formation, structure, and evolution of both the Sun and our Solar System. Furthermore, it is an essential ...reference standard against which the elemental contents of other astronomical objects are compared. In this review, we evaluate the current understanding of the solar photospheric composition. In particular, we present a redetermination of the abundances of nearly all available elements, using a realistic new three-dimensional (3D), time-dependent hydrodynamical model of the solar atmosphere. We have carefully considered the atomic input data and selection of spectral lines, and accounted for departures from local thermodynamic equilibrium (LTE) whenever possible. The end result is a comprehensive and homogeneous compilation of the solar elemental abundances. Particularly noteworthy findings are significantly lower abundances of C, N, O, and Ne compared to the widely used values of a decade ago. The new solar chemical composition is supported by a high degree of internal consistency between available abundance indicators, and by agreement with values obtained in the Solar Neighborhood and from the most pristine meteorites. There is, however, a stark conflict with standard models of the solar interior according to helioseismology, a discrepancy that has yet to find a satisfactory resolution.
Tracking emissions in the US electricity system de Chalendar, Jacques A.; Taggart, John; Benson, Sally M.
Proceedings of the National Academy of Sciences,
12/2019, Letnik:
116, Številka:
51
Journal Article
Recenzirano
Odprti dostop
Understanding electricity consumption and production patterns is a necessary first step toward reducing the health and climate impacts of associated emissions. In this work, the economic input–output ...model is adapted to track emissions flows through electric grids and quantify the pollution embodied in electricity production, exchanges, and, ultimately, consumption for the 66 continental US Balancing Authorities (BAs). The hourly and BA-level dataset we generate and release leverages multiple publicly available datasets for the year 2016. Our analysis demonstrates the importance of considering location and temporal effects as well as electricity exchanges in estimating emissions footprints. While increasing electricity exchanges makes the integration of renewable electricity easier, importing electricity may also run counter to climate-change goals, and citizens in regions exporting electricity from high-emission-generating sources bear a disproportionate air-pollution burden. For example, 40% of the carbon emissions related to electricity consumption in California’s main BA were produced in a different region. From 30 to 50% of the sulfur dioxide and nitrogen oxides released in some of the coal-heavy Rocky Mountain regions were related to electricity produced that was then exported. Whether for policymakers designing energy efficiency and renewable programs, regulators enforcing emissions standards, or large electricity consumers greening their supply, greater resolution is needed for electricsector emissions indices to evaluate progress against current and future goals.
The programmed death-1 (PD-1) molecule is involved in peripheral tolerance and in the immune escape mechanisms during chronic viral infections and cancer. PD-1 interacts with two ligands, PD-L1 and ...PD-L2. We have investigated the molecular mechanisms of PD-1 interactions with its ligands by surface plasmon resonance and cell surface binding as well as the ability of the two ligands to compete for PD-1 binding. PD-L1 and PD-L2 bound PD-1 with comparable affinities, but striking differences were observed at the level of the association and dissociation characteristics. PD-L1, but not PD-L2, had a delayed interaction reminiscent of a phenomenon of conformational transition. These mechanisms were confirmed by using PD-L1 mAbs that delayed the dissociation of PD-L1 from PD-1. This mechanism was not restricted to PD-1 binding since PD-L1 behaved in a similar manner with its second ligand, CD80. Finally, we could demonstrate that PD-L1 and PD-L2 competed for PD-1 binding and conversely, an antagonist PD-1 mAb blocked both PD-L1 and PD-L2 binding to PD-1 and strongly enhanced T-cell proliferation. These data further emphasize the differential molecular mechanisms of interaction of PD-L1 and PD-L2 with PD-1, and suggest possible new approach for the therapy of chronic infection, cancer and transplantation.
How the thymus shaped immunology
The function of the thymus was discovered by Jacques Miller in 1961 and laid a foundation for immunology and modern medicine. Until that time, researchers mistakenly ...believed the thymus merely represented a remnant of defunct lymph tissue, something of an immune cell graveyard. In a Review, Miller recounts the seminal experiments and conceptual thinking that led to uncovering the critical function of the thymus and provides insights that can be learned from those early days. How knowledge of thymus function subsequently spawned the field of T cell biology and the impact it has had on immune cell interactions, vaccination, cancer immunotherapy, and the microbiome are also discussed.
Science
, this issue p.
eaba2429
BACKGROUND
Until the 1960s, the thymus had long remained an enigmatic organ with no known function or was considered to be just a “graveyard” for dying lymphocytes. By contrast, the circulating small lymphocytes found in blood and lymph had been shown in the late 1950s to be long-lived cells able to initiate an immune response when appropriately stimulated by antigen. However, although the thymus was known to be populated with lymphocytes, immunologists had not attributed any immune function to the organ. There were many reasons for this. For example, the cytological hallmarks of an immune response, such as the presence of plasma cells and germinal centers, were not seen in the thymus of healthy animals even after extensive immunization. Thymus lymphocytes, unlike lymphocytes from blood and lymphoid tissues, were unable to mount an immune response on transfer to immunocompromised recipients. Furthermore, thymectomy, which had always been performed in adult animals, was not associated with any immune defects.
ADVANCES
In 1961, thymectomy was performed in mice during the immediate neonatal period and revealed the critically important function of the thymus in enabling the development of the immune system. Neonatally thymectomized (NTx) mice were highly susceptible to intercurrent infections, deficient in lymphocytes, unable to reject foreign skin grafts or produce antibody to some (though not all) antigens, and prone to developing certain tumors. There was no major immune defect after adult thymectomy unless the lymphoid tissues had been damaged by total body irradiation. Implanting thymus tissue into NTx mice or irradiated adult thymectomized mice restored immune function. When the thymus graft was taken from a foreign strain, the thymectomized recipients were found to be specifically tolerant of the histocompatibility antigens of the donor. This implied that the thymus was responsible not only for the normal development of immune functions but also for imposing tolerance to the body’s own tissues.
The thymus was shown to seed the lymphoid system with T lymphocytes that migrated to certain discrete areas of the lymphoid tissues and recirculated from the blood through lymphoid tissues, lymph, and back to the bloodstream. T cells exiting the thymus were found to be responsible for killing infected cells and for rejecting foreign tissue grafts. Therefore, T cells could soon be subdivided into subsets based on function, cell surface markers, and secreted products or interleukins. Thymus lymphoid stem cells were subsequently identified, and the epithelial and dendritic cells in the thymus were shown to greatly influence T cell development. They were able to educate T cells to recognize a great diversity of peptide antigens bound to the body’s own markers, major histocompatibility complex molecules, but purged any T cells that strongly reacted against the body’s own self-components. The use of irradiated adult thymectomized mice showed that T cells were not the precursors of antibody-forming cells but were essential to help, through some type of collaboration, other lymphocytes originating in bone marrow (B cells) to respond to antigen by producing antibody.
OUTLOOK
The discovery of thymus function and of T and B cell collaboration was a major immunological milestone because it not only opened up the field of immune cell interactions but also changed the course of immunology and medicine. It promoted the need for all immune phenomena, for example, memory, tolerance, autoimmunity, and immunodeficiency, as well as inflammatory and immunopathological disease conditions, to be reassessed in terms of the role played by the two distinct sets of lymphocytes and their subsets. We now know that T cells are involved in the entire spectrum of tissue physiology and pathology and even in situations not considered to be bona fide immunological conditions, such as tissue repair, dysbiosis, eclampsia, senescence, and cancer.
Origin and migration of T and B cells.
Hemopoietic stem cells originating in the yolk sac, fetal liver, or bone marrow migrate through the blood to the thymus, where they differentiate into T lymphocytes. Others differentiate within the bone marrow in mammals, or the bursa of Fabricius in birds, to produce B cells. Mature T and B cells circulate in the blood and lymph and colonize the T and B cell compartments of the lymphoid tissues.
Reprinted with permission from the Royal Society, London
The lymphoid system is intimately involved in immunological processes. The small lymphocyte that circulates through blood into lymphoid tissues, then through the lymph and back to the blood through the thoracic duct, is able to initiate immune responses after appropriate stimulation by antigen. However, the lymphocytes found in the thymus are deficient in this ability despite the fact that the thymus plays a central role in lymphocyte production and in ensuring the normal development of immunological faculty. During embryogenesis, lymphocytes are present in the thymus before they can be identified in the circulation and in other lymphoid tissues. They become “educated” in the thymus to recognize a great diversity of peptide antigens bound to the body’s own marker antigen, the major histocompatibility complex, but they are purged if they strongly react against their own self-components. Lymphocytes differentiate to become various T cell subsets and then exit through the bloodstream to populate certain areas of the lymphoid system as peripheral T lymphocytes with distinct markers and immune functions.
The last decade has seen a dramatic increase in the use of small‐angle scattering for the study of biological macromolecules in solution. The drive for more complete structural characterization of ...proteins and their interactions, coupled with the increasing availability of instrumentation and easy‐to‐use software for data analysis and interpretation, is expanding the utility of the technique beyond the domain of the biophysicist and into the realm of the protein scientist. However, the absence of publication standards and the ease with which 3D models can be calculated against the inherently 1D scattering data means that an understanding of sample quality, data quality, and modeling assumptions is essential to have confidence in the results. This review is intended to provide a road map through the small‐angle scattering experiment, while also providing a set of guidelines for the critical evaluation of scattering data. Examples of current best practice are given that also demonstrate the power of the technique to advance our understanding of protein structure and function.
Natural Killer Cell Signaling Pathways Vivier, Eric; Nunès, Jacques A.; Vély, Frédéric
Science (American Association for the Advancement of Science),
11/2004, Letnik:
306, Številka:
5701
Journal Article
Recenzirano
Natural killer (NK) cells are lymphocytes of the innate immune system that are involved in the early defenses against foreign cells, as well as autologous cells undergoing various forms of stress, ...such as microbial infection or tumor transformation. NK cell activation is controlled by a dynamic balance between complementary and antagonistic pathways that are initiated upon interaction with potential target cells. NK cells express an array of activating cell surface receptors that can trigger cytolytic programs, as well as cytokine or chemokine secretion. Some of these activating cell surface receptors initiate protein tyrosine kinase (PTK)-dependent pathways through noncovalent associations with transmembrane signaling adaptors that harbor intracytoplasmic ITAMs (immunoreceptor tyrosine-based activation motifs). Additional cell surface receptors that are not directly coupled to ITAMs also participate in NK cell activation. These include NKG2D, which is noncovalently associated to the DAP10 transmembrane signaling adaptor, as well as integrins and cytokine receptors. NK cells also express cell surface inhibitory receptors that antagonize activating pathways through protein tyrosine phosphatases (PTPs). These inhibitory cell surface receptors are characterized by intracytoplasmic ITIMs (immunoreceptor tyrosine-based inhibition motifs). The tyrosine-phosphorylation status of several signaling components that are substrates for both PTKs and PTPs is thus key to the propagation of the NK cell effector pathways. Understanding the integration of these multiple signals is central to the understanding and manipulation of NK cell effector signaling pathways.
This article describes a reduction in childhood vaccinations during the COVID‐19 pandemic, which may leave communities more vulnerable to vaccine‐preventable diseases.
PDF
