Sources of cosmic dust in the Earth's atmosphere Carrillo‐Sánchez, J. D.; Nesvorný, D.; Pokorný, P. ...
Geophysical research letters,
16 December 2016, Letnik:
43, Številka:
23
Journal Article
Recenzirano
Odprti dostop
There are four known sources of dust in the inner solar system: Jupiter Family comets, asteroids, Halley Type comets, and Oort Cloud comets. Here we combine the mass, velocity, and radiant ...distributions of these cosmic dust populations from an astronomical model with a chemical ablation model to estimate the injection rates of Na and Fe into the Earth's upper atmosphere, as well as the flux of cosmic spherules to the surface. Comparing these parameters to lidar observations of the vertical Na and Fe fluxes above 87.5 km, and the measured cosmic spherule accretion rate at South Pole, shows that Jupiter Family Comets contribute (80 ± 17)% of the total input mass (43 ± 14 t d−1), in good accord with Cosmic Background Explorer and Planck observations of the zodiacal cloud.
Plain Language Summary
The solar system contains a significant quantity of cosmic dust. This is generated from comets when they orbit close to the sun and evaporate, and also from collisions between asteroids in the region between Mars and Jupiter. The amount of cosmic dust which enters the Earth's atmosphere every day is highly uncertain, ranging from 5 to 270 tonnes. This study combines an astronomical model of dust in the solar system with a model describing the fate of dust particles when they enter the atmosphere at high speed. The dust input is then constrained with three observations: the rate of injection of sodium atoms into the upper atmosphere where some of this dust evaporates; the rate of injection of iron atoms; and the rate of accumulation of cosmic spherules (meteorites that melted during atmospheric entry) at the South Pole. The conclusion is that about 80% of the dust comes from comets with short orbital periods (less than 20 years), and the daily input is between 29 and 57 tonnes.
Key Points
Solar system dust sources are fitted to the cosmic spherule accretion rate and the Na and Fe fluxes in the mesosphere
Jupiter Family Comets provide ~80% of the cosmic dust entering the atmosphere, with 12% from long‐period comets and 8% from asteroids
The resulting differential ablation of Ca and Fe relative to Na explains the relative abundances of these metal layers in the mesosphere
The size and velocity distribution of cosmic dust particles entering the Earth's atmosphere is uncertain. Here we show that the relative concentrations of metal atoms in the upper mesosphere, and the ...surface accretion rate of cosmic spherules, provide sensitive probes of this distribution. Three cosmic dust models are selected as case studies: two are astronomical models, the first constrained by infrared observations of the Zodiacal Dust Cloud and the second by radar observations of meteor head echoes; the third model is based on measurements made with a spaceborne dust detector. For each model, a Monte Carlo sampling method combined with a chemical ablation model is used to predict the ablation rates of Na, K, Fe, Mg, and Ca above 60 km and cosmic spherule production rate. It appears that a significant fraction of the cosmic dust consists of small (<5 µg) and slow (<15 km s−1) particles.
Key Points
The atmospheric impacts of three cosmic dust models are compared
Slow cometary particles produce the measured cosmic spherule accretion rate
These particles also produce significant differential ablation in the mesosphere
Both IDH1 mutation and MGMT promoter methylation are associated with longer survival. We investigated the ability of imaging correlates to serve as noninvasive biomarkers for these molecularly ...defined GBM subtypes.
MR imaging from 202 patients with GBM was retrospectively assessed for nonenhancing tumor and edema among other imaging features. IDH1 mutational and MGMT promoter methylation status were determined by DNA sequencing and methylation-specific PCR, respectively. Overall survival was determined by using a multivariate Cox model and the Kaplan-Meier method with a log rank test. A logistic regression model followed by ROC analysis was used to classify the IDH1 mutation and methylation status by using imaging features.
MGMT promoter methylation and IDH1 mutation were associated with longer median survival. Edema levels stratified survival for methylated but not unmethylated tumors. Median survival for methylated tumors with little/no edema was 2476 days (95% CI, 795), compared with 586 days (95% CI, 507-654) for unmethylated tumors or tumors with edema. All IDH1 mutant tumors were nCET positive, and most (11/14, 79%) were located in the frontal lobe. Imaging features including larger tumor size and nCET could be used to determine IDH1 mutational status with 97.5% accuracy, but poorly predicted MGMT promoter methylation.
Imaging features are potentially predictive of IDH1 mutational status but were poorly correlated with MGMT promoter methylation. Edema stratifies survival in MGMT promoter methylated but not in unmethylated tumors; patients with methylated tumors with little or no edema have particularly long survival.
Defining and targeting health care access barriers Carrillo, J Emilio; Carrillo, Victor A; Perez, Hector R ...
Journal of health care for the poor and underserved,
05/2011, Letnik:
22, Številka:
2
Journal Article
Recenzirano
The impact of social and economic determinants of health status and the existence of racial and ethnic health care access disparities have been well-documented. This paper describes a model, the ...Health Care Access Barriers Model (HCAB), which provides a taxonomy and practical framework for the classification, analysis and reporting of those modifiable health care access barriers that are associated with health care disparities. The model describes three categories of modifiable health care access barriers: financial, structural, and cognitive. The three types of barriers are reciprocally reinforcing and affect health care access individually or in concert. These barriers are associated with screening, late presentation to care, and lack of treatment, which in turn result in poor health outcomes and health disparities. By targeting those barriers that are measurable and modifiable the model facilitates root-cause analysis and intervention design.
The use of next-generation sequencing technologies has enabled the rapid identification of non-synonymous somatic mutations in cancer cells. Neoantigens are mutated peptides derived from somatic ...mutations not present in normal tissues that may result in the presentation of tumour-specific peptides capable of eliciting antitumour T-cell responses. Personalised neoantigen-based cancer vaccines and adoptive T-cell therapies have been shown to prime host immunity against tumour cells and are under clinical trial development. However, the optimisation and standardisation of neoantigen identification, as well as its delivery as immunotherapy are needed to increase tumour-specific T-cell responses and, thus, the clinical efficacy of current cancer immunotherapies.
In this recommendation article, launched by the European Society for Medical Oncology (ESMO), we outline and discuss the available framework for neoantigen prediction and present a systematic review of the current scientific evidence.
A number of computational pipelines for neoantigen prediction are available. Most of them provide peptide major histocompatibility complex (MHC) binding affinity predictions, but more recent approaches incorporate additional features like variant allele fraction, gene expression, and clonality of mutations. Neoantigens can be predicted in all cancer types with high and low tumour mutation burden, in part by exploiting tumour-specific aberrations derived from mutational frameshifts, splice variants, gene fusions, endogenous retroelements and other tumour-specific processes that could yield more potently immunogenic tumour neoantigens. Ongoing clinical trials will highlight those cancer types and combinations of immune therapies that would derive the most benefit from neoantigen-based immunotherapies.
Improved identification, selection and prioritisation of tumour-specific neoantigens are needed to increase the scope of benefit from cancer vaccines and adoptive T-cell therapies. Novel pipelines are being developed to resolve the challenges posed by high-throughput sequencing and to predict immunogenic neoantigens.
•Next-generation sequencing technologies have provided the means to directly identify somatic gene mutations in tumours.•Neoantigens are tumour-specific mutated peptides capable of inducing antitumour immune responses.•The discovery of immunogenic neoantigens is instrumental for the pursuit of cancer vaccines and adoptive T-cell therapy.•Refining computational workflows towards the optimal identification of immunogenic neoepitopes is needed.
We study the McKean–Vlasov equation
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with periodic boundary conditions on the torus. We first study the global asymptotic stability of the homogeneous ...steady state. We then focus our attention on the stationary system, and prove the existence of nontrivial solutions branching from the homogeneous steady state, through possibly infinitely many bifurcations, under appropriate assumptions on the interaction potential. We also provide sufficient conditions for the existence of continuous and discontinuous phase transitions. Finally, we showcase these results by applying them to several examples of interaction potentials such as the noisy Kuramoto model for synchronisation, the Keller–Segel model for bacterial chemotaxis, and the noisy Hegselmann–Krausse model for opinion dynamics.
We analyze under which conditions equilibration between two competing effects, repulsion modeled by nonlinear diffusion and attraction modeled by nonlocal interaction, occurs. This balance leads to ...continuous compactly supported radially decreasing equilibrium configurations for all masses. All stationary states with suitable regularity are shown to be radially symmetric by means of continuous Steiner symmetrization techniques. Calculus of variations tools allow us to show the existence of global minimizers among these equilibria. Finally, in the particular case of Newtonian interaction in two dimensions they lead to uniqueness of equilibria for any given mass up to translation and to the convergence of solutions of the associated nonlinear aggregation-diffusion equations towards this unique equilibrium profile up to translations as
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The mesosphere/lower thermosphere (MLT, 80–100 km) region is an important boundary between Earth's atmosphere below and space above and may act as a sensitive indicator for anthropogenic climate ...change. Existing observational and modeling studies have shown the middle atmosphere and the MLT is cooling and contracting because of increasing greenhouse gas emissions. However, trend analyses are highly sensitive to the time periods covered, their length, and the measurement type and methodology used. We present for the first time the linear and 11‐year solar cycle responses in the meteor ablation altitude distributions observed by 12 meteor radars at different locations. Decreasing altitudes were seen at all latitudes (linear trends varying from −10.97 to −817.95 m dec−1), and a positive correlation with solar activity was seen for most locations. The divergence of responses at high latitudes indicates an important and complex interplay between atmospheric changes and dynamics at varying time scales.
Plain Language Summary
High up in our atmosphere lies the mesosphere/lower thermosphere region (80–100 km); an important transition zone between the atmosphere below and space above. Existing studies indicate that this region is changing (cooling and contracting) in response to increasing greenhouse gas emissions, quite unlike the net warming we see near the surface. However these trend studies are often highly sensitive to choice and length of time period covered, and the methodology and type of measurements used. Here we present for the first time a self‐consistent methodology applied to 12 different meteor radar station datasets located at a diverse range of latitudes. We looked at changes in the mean peak altitude of individual meteoroid detections, and found decreasing peak altitudes at all locations examined (linear trends varying from −10.97 to −817.95 m decade−1) consistent with a global cooling and contracting of the upper atmosphere. We also examined the response to the 11‐year solar cycle and found a positive correlation with solar activity (i.e., increased meteoroid peak altitudes during solar maximum, and vice versa) for low and mid‐latitude locations. However we found an anti‐correlation at high latitudes suggestive of an important and complex interplay between atmospheric changes and dynamics at varying time scales.
Key Points
Use of geographically diverse meteor radar peak detection altitudes to assess long‐term and 11‐year solar cycle (SC) trends in mesopause region
The altitude of observed peak meteor height has decreased over time at all locations, regardless of latitude and data set
Positive correlation at low‐ and mid‐latitude locations with the 11‐year SC, but more complex response at high‐latitudes
In this work we consider local minimizers (in the topology of transport distances) of the interaction energy associated with a repulsive–attractive potential. We show how the dimensionality of the ...support of local minimizers is related to the repulsive strength of the potential at the origin.
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