111 research outputs found
Studies of Relativistic Jets in Active Galactic Nuclei with SKA
Relativistic jets in active galactic nuclei (AGN) are among the most powerful
astrophysical objects discovered to date. Indeed, jetted AGN studies have been
considered a prominent science case for SKA, and were included in several
different chapters of the previous SKA Science Book (Carilli & Rawlings 2004).
Most of the fundamental questions about the physics of relativistic jets still
remain unanswered, and await high-sensitivity radio instruments such as SKA to
solve them. These questions will be addressed specially through analysis of the
massive data sets arising from the deep, all-sky surveys (both total and
polarimetric flux) from SKA1. Wide-field very-long-baseline-interferometric
survey observations involving SKA1 will serve as a unique tool for
distinguishing between extragalactic relativistic jets and star forming
galaxies via brightness temperature measurements. Subsequent SKA1 studies of
relativistic jets at different resolutions will allow for unprecedented
cosmological studies of AGN jets up to the epoch of re-ionization, enabling
detailed characterization of the jet composition, magnetic field, particle
populations, and plasma properties on all scales. SKA will enable us to study
the dependence of jet power and star formation on other properties of the AGN
system. SKA1 will enable such studies for large samples of jets, while VLBI
observations involving SKA1 will provide the sensitivity for pc-scale imaging,
and SKA2 (with its extraordinary sensitivity and dynamic range) will allow us
for the first time to resolve and model the weakest radio structures in the
most powerful radio-loud AGN.Comment: 19 pages, 4 figures; to appear as part of 'Cosmic Magnetism' in
Proceedings 'Advancing Astrophysics with the SKA (AASKA14)', PoS(AASKA14_093
Relativistic Magnetohydrodynamics with Application to Gamma-Ray Burst Outflows: I. Theory and Semianalytic Trans-Alfvenic Solutions
We present a general formulation of special-relativistic magnetohydrodynamics
and derive exact radially self-similar solutions for axisymmetric outflows from
strongly magnetized, rotating compact objects. We generalize previous work by
including thermal effects and analyze in detail the various forces that guide,
accelerate, and collimate the flow. We demonstrate that, under the assumptions
of a quasi-steady poloidal magnetic field and of a highly relativistic poloidal
velocity, the equations become effectively time-independent and the motion can
be described as a frozen pulse. We concentrate on trans-Alfvenic solutions and
consider outflows that are super-Alfvenic throughout in the companion paper.
Our results are applicable to relativistic jets in gamma-ray burst (GRB)
sources, active galactic nuclei, and microquasars, but our discussion focuses
on GRBs. We envision the outflows in this case to initially consist of a hot
and optically thick mixture of baryons, electron-positron pairs, and photons.
We show that the flow is at first accelerated thermally but that the bulk of
the acceleration is magnetic, with the asymptotic Lorentz factor corresponding
to a rough equipartition between the Poynting and kinetic-energy fluxes (i.e.,
\~50% of the injected total energy is converted into baryonic kinetic energy).
The electromagnetic forces also strongly collimate the flow, giving rise to an
asymptotically cylindrical structure.Comment: 22 pages, 5 figures, submitted to the Astrophysical Journal. The
companion paper is astro-ph/030348
Recommended from our members
Harmonized gap-filled datasets from 20 urban flux tower sites
A total of 20 urban neighbourhood-scale eddy covariance flux tower datasets are made openly available after being harmonized to create a 50 site-year collection with broad diversity in climate and urban surface characteristics. Variables needed as inputs for land surface models (incoming radiation, temperature, humidity, air pressure, wind and precipitation) are quality controlled, gap-filled and prepended with 10 years of reanalysis-derived local data, enabling an extended spin up to equilibrate models with local climate conditions. For both gap filling and spin up, ERA5 reanalysis meteorological data are bias corrected using tower-based observations, accounting for diurnal, seasonal and local urban effects not modelled in ERA5. The bias correction methods developed perform well compared to methods used in other datasets (e.g. WFDE5 or FLUXNET2015). Other variables (turbulent and upwelling radiation fluxes) are harmonized and quality controlled without gap filling Site description metadata include local land cover fractions (buildings, roads, trees, grass etc.), building height and morphology, aerodynamic roughness estimates, population density and satellite imagery. This open collection can help extend our understanding of urban environmental processes through observational synthesis studies or in the evaluation of land surface environmental models in a wide range of urban settings. These data can be accessed from https://doi.org/10.5281/zenodo.7104984 (Lipson et al., 2022).Peer reviewe
Chemical analysis of Greek pollen - Antioxidant, antimicrobial and proteasome activation properties
<p>Abstract</p> <p>Background</p> <p>Pollen is a bee-product known for its medical properties from ancient times. In our days is increasingly used as health food supplement and especially as a tonic primarily with appeal to the elderly to ameliorate the effects of ageing. In order to evaluate the chemical composition and the biological activity of Greek pollen which has never been studied before, one sample with identified botanical origin from sixteen different common plant taxa of Greece has been evaluated.</p> <p>Results</p> <p>Three different extracts of the studied sample of Greek pollen, have been tested, in whether could induce proteasome activities in human fibroblasts. The water extract was found to induce a highly proteasome activity, showing interesting antioxidant properties. Due to this activity the aqueous extract was further subjected to chemical analysis and seven flavonoids have been isolated and identified by modern spectral means. From the methanolic extract, sugars, lipid acids, phenolic acids and their esters have been also identified, which mainly participate to the biosynthetic pathway of pollen phenolics. The total phenolics were estimated with the Folin-Ciocalteau reagent and the total antioxidant activity was determined by the DPPH method while the extracts and the isolated compounds were also tested for their antimicrobial activity by the dilution technique.</p> <p>Conclusions</p> <p>The Greek pollen is rich in flavonoids and phenolic acids which indicate the observed free radical scavenging activity, the effects of pollen on human fibroblasts and the interesting antimicrobial profile.</p
b-tagging in DELPHI at LEP
Abstract: The standard method used for tagging b-hadrons in the DELPHI experiment at the CERN LEP Collider is discussed in detail. The main ingredient of b-tagging is the impact parameters of tracks, which relies mostly on the vertex detector. Additional information, such as the mass of particles associated to a secondary vertex, significantly improves the selection efficiency and the background suppression. The paper describes various discriminating variables used for the tagging and the procedure of their combination. In addition, applications of b-tagging to some physics analyses, which depend crucially on the performance and reliability of b-tagging, are described briefly
Molecular mechanisms of cell death: recommendations of the Nomenclature Committee on Cell Death 2018.
Over the past decade, the Nomenclature Committee on Cell Death (NCCD) has formulated guidelines for the definition and interpretation of cell death from morphological, biochemical, and functional perspectives. Since the field continues to expand and novel mechanisms that orchestrate multiple cell death pathways are unveiled, we propose an updated classification of cell death subroutines focusing on mechanistic and essential (as opposed to correlative and dispensable) aspects of the process. As we provide molecularly oriented definitions of terms including intrinsic apoptosis, extrinsic apoptosis, mitochondrial permeability transition (MPT)-driven necrosis, necroptosis, ferroptosis, pyroptosis, parthanatos, entotic cell death, NETotic cell death, lysosome-dependent cell death, autophagy-dependent cell death, immunogenic cell death, cellular senescence, and mitotic catastrophe, we discuss the utility of neologisms that refer to highly specialized instances of these processes. The mission of the NCCD is to provide a widely accepted nomenclature on cell death in support of the continued development of the field
Mitochondrial physiology
As the knowledge base and importance of mitochondrial physiology to evolution, health and disease expands, the necessity for harmonizing the terminology concerning mitochondrial respiratory states and rates has become increasingly apparent. The chemiosmotic theory establishes the mechanism of energy transformation and coupling in oxidative phosphorylation. The unifying concept of the protonmotive force provides the framework for developing a consistent theoretical foundation of mitochondrial physiology and bioenergetics. We follow the latest SI guidelines and those of the International Union of Pure and Applied Chemistry (IUPAC) on terminology in physical chemistry, extended by considerations of open systems and thermodynamics of irreversible processes. The concept-driven constructive terminology incorporates the meaning of each quantity and aligns concepts and symbols with the nomenclature of classical bioenergetics. We endeavour to provide a balanced view of mitochondrial respiratory control and a critical discussion on reporting data of mitochondrial respiration in terms of metabolic flows and fluxes. Uniform standards for evaluation of respiratory states and rates will ultimately contribute to reproducibility between laboratories and thus support the development of data repositories of mitochondrial respiratory function in species, tissues, and cells. Clarity of concept and consistency of nomenclature facilitate effective transdisciplinary communication, education, and ultimately further discovery
Mitochondrial physiology
As the knowledge base and importance of mitochondrial physiology to evolution, health and disease expands, the necessity for harmonizing the terminology concerning mitochondrial respiratory states and rates has become increasingly apparent. The chemiosmotic theory establishes the mechanism of energy transformation and coupling in oxidative phosphorylation. The unifying concept of the protonmotive force provides the framework for developing a consistent theoretical foundation of mitochondrial physiology and bioenergetics. We follow the latest SI guidelines and those of the International Union of Pure and Applied Chemistry (IUPAC) on terminology in physical chemistry, extended by considerations of open systems and thermodynamics of irreversible processes. The concept-driven constructive terminology incorporates the meaning of each quantity and aligns concepts and symbols with the nomenclature of classical bioenergetics. We endeavour to provide a balanced view of mitochondrial respiratory control and a critical discussion on reporting data of mitochondrial respiration in terms of metabolic flows and fluxes. Uniform standards for evaluation of respiratory states and rates will ultimately contribute to reproducibility between laboratories and thus support the development of data repositories of mitochondrial respiratory function in species, tissues, and cells. Clarity of concept and consistency of nomenclature facilitate effective transdisciplinary communication, education, and ultimately further discovery
Molecular definitions of autophagy and related processes.
Over the past two decades, the molecular machinery that underlies autophagic responses has been characterized with ever increasing precision in multiple model organisms. Moreover, it has become clear that autophagy and autophagy-related processes have profound implications for human pathophysiology. However, considerable confusion persists about the use of appropriate terms to indicate specific types of autophagy and some components of the autophagy machinery, which may have detrimental effects on the expansion of the field. Driven by the overt recognition of such a potential obstacle, a panel of leading experts in the field attempts here to define several autophagy-related terms based on specific biochemical features. The ultimate objective of this collaborative exchange is to formulate recommendations that facilitate the dissemination of knowledge within and outside the field of autophagy research
- …