scholarly journals The shearing sheet and swing amplification revisited

2020 ◽  
Vol 496 (1) ◽  
pp. 767-783
Author(s):  
James Binney
Keyword(s):  
Dispersion Relation ◽  
Narrow Range ◽  
Real Space ◽  
Angular Momenta ◽  
Limited Life ◽  
Quantitative Understanding ◽  
The Impact ◽  
Axisymmetric Disturbances ◽  
Lindblad Resonance ◽  
Inner Lindblad Resonance

ABSTRACT The principal results of the classic analysis of the shearing sheet and swing amplification by Julian and Toomre (JT) are re-derived in a more accessible way and used to gain a better quantitative understanding of the dynamics of stellar discs. The axisymmetric limit of the shearing sheet is derived and used to re-derive Kalnajs’ 1965 dispersion relation and Toomre’s 1964 stability criterion for axisymmetric disturbances. Using the shearing sheet to revisit Toomre’s important 1969 paper on the group velocity implied by the Lin–Shu–Kalnajs (LSK) dispersion relation, we discover that two wavepackets emerge inside corotation: one each side of the inner Lindblad resonance. An extended form of the JT equation is used to investigate the impact of there being a deficit or surplus of stars in a narrow range of angular momenta. Swing amplification of leading waves introduced by such a groove gives rise to transient trailing spirals that extend further in radius and live longer at smaller azimuthal wavenumbers. Although the LSK dispersion relation provides useful interpretations of wavepackets, the shearing sheet highlights the limitations of the LSK approach to disc dynamics. Disturbances do not avoid an annulus around corotation, as the LSK dispersion relation implies. While disturbances of the shearing sheet have a limited life in real space, they live on much longer in velocity space, which Gaia allows us to probe extensively. c++ code is provided to facilitate applications of winding spiral waves.

scholarly journals Compact Array Mapping of the Nuclear Starburst in NGC 7552

1994 ◽  
Vol 158 ◽  
pp. 355-357
Author(s):  
Duncan A. Forbes ◽  
Ray P. Norris ◽  
Gerry M. Williger ◽  
R. Chris Smith
Keyword(s):  
High Resolution ◽  
Near Infrared ◽  
Starburst Galaxy ◽  
Angular Momenta ◽  
Lindblad Resonance ◽  
Inner Lindblad Resonance ◽  
Compact Array

We discuss new observations of the starburst galaxy NGC 7552. From optical and near–infrared colour maps we find a red, dusty circumnuclear ring. High-resolution radio mapping from the ATCA reveals the same ring, and a number of bright blobs (probably SNRs). The ring is probably associated with gas and dust which have lost angular momenta due to torques in the bar potential and settled at the inner Lindblad resonance. These circumnuclear starburst rings may be relatively common (when mapped without the obscuring affects of dust) and may play a role in collimating material of a nuclear outflow.

Lysistrata

2018 ◽  
Author(s):  
Nurit Yaari
Keyword(s):  
Narrow Range ◽  
Historical Events ◽  
State Management ◽  
The Impact ◽  
The City

This chapter focuses on the comedy Lysistrata by Aristophanes. Lysistrata is the most commonly staged of Aristophanes’ comedies in Israel; to date seven productions of that play have been staged in Israel. This is not surprising, given that it is a lurid anti-war comedy, with a plot that combines sex and war, and raises weighty issues concerning state management, war fatigue, and the desire for peace, in a fantasy where women take over control of the city. Through an analysis of four productions of that play that have been staged in Israel between 1958 and 2002, the chapter discusses the impact of historical events on the reading of the play and its performance, and shows how each production steered in the narrow range between entertainment, criticism, and protest.

scholarly journals The Early Days of Personal Solar Ultraviolet Dosimetry

Atmosphere ◽  
2020 ◽  
Vol 11 (2) ◽  
pp. 125 ◽  
Author(s):  
Brian Diffey
Keyword(s):  
Uv Radiation ◽  
Human Exposure ◽  
Ground Level ◽  
Uv Exposure ◽  
Population Exposure ◽  
Atmospheric Ozone ◽  
Quantitative Understanding ◽  
Solar Uv ◽  
The Impact ◽  
Solar Ultraviolet

In the early 1970s, environmental conservationists were becoming concerned that a reduction in the thickness of the atmospheric ozone layer would lead to increased levels of ultraviolet (UV) radiation at ground level, resulting in higher population exposure to UV and subsequent harm, especially a rise in skin cancer. At the time, no measurements had been reported on the normal levels of solar UV radiation which populations received in their usual environment, so this lack of data, coupled with increasing concerns about the impact to human health, led to the development of simple devices that monitored personal UV exposure. The first and most widely used UV dosimeter was the polymer film, polysulphone, and this review describes its properties and some of the pioneering studies using the dosimeter that led to a quantitative understanding of human exposure to sunlight in a variety of behavioral, occupational, and geographical settings.

scholarly journals Plant protection products in organic grapevine growing

2010 ◽  
Vol 55 (1) ◽  
pp. 103-122 ◽  
Author(s):  
Branislava Sivcev ◽  
Ivan Sivcev ◽  
Zorica Rankovic-Vasic
Keyword(s):  
Preventive Measures ◽  
Narrow Range ◽  
Plant Protection ◽  
Plant Protection Products ◽  
Organic Production ◽  
Plant Origin ◽  
Biological Products ◽  
Harmful Organisms ◽  
Bunch Rot ◽  
The Impact

Pests and grapevine diseases in organic production are suppressed by preventive measures with a view to reducing the impact of the attack. Allowed substances acting on patogenous fungi, insects, mites and other harmful organisms are used, if appropriate. Insecticides of plant origin are used in the organic production of grapevine, as well as vegetable oils, powders and insecticidal soaps that are selective, with a narrow range of effects and of lower toxicity, as well as biological products. As a rule, such plant protection products require a more frequent application. Copper-based and sulphur-based fungicides are still leading products in suppressing grapevine diseases. Researches are directed to decrease the quantity of application and to find their replacement by also efficient fungicides. A special emphasis is put on researching the efficient fungicides for suppressing Botrytis bunch rot and factors causing grapevine wood diseases (Esca and Eutypa) in organic production. Along with copper and sulphur, different substances such as bicarbonates, plant extracts and oils, biological products being parasites, patogenous or diseases agent antagonists, and natural products such as milk and whey are applied in the organic production of grapevine.

scholarly journals A Data Driven Change-point Epidemic Model for Assessing the Impact of Large Gathering and Subsequent Movement Control Order on COVID-19 Spread in Malaysia

2020 ◽  
Author(s):  
Sarat C. Dass ◽  
Wai M. Kwok ◽  
Gavin J. Gibson ◽  
Balvinder S. Gill ◽  
Bala M. Sundram ◽  
...  
Keyword(s):  
Change Point ◽  
Movement Control ◽  
Disease Spread ◽  
Time Period ◽  
Before And After ◽  
Quantitative Understanding ◽  
Control Order ◽  
Short Time ◽  
The Impact ◽  
Second Wave

AbstractThe second wave of COVID-19 in Malaysia is largely attributed to a mass gathering held in Sri Petaling between February 27, 2020 and March 1, 2020, which contributed to an exponential rise of COVID-19 cases in the country. Starting March 18, 2020, the Malaysian government introduced four consecutive phases of a Movement Control Order (MCO) to stem the spread of COVID-19. The MCO was implemented through various non-pharmaceutical interventions (NPIs). The reported number of cases reached its peak by the first week of April and then started to reduce, hence proving the effectiveness of the MCO. To gain a quantitative understanding of the effect of MCO on the dynamics of COVID-19, this paper develops a class of mathematical models to capture the disease spread before and after MCO implementation in Malaysia. A heterogeneous variant of the Susceptible-Exposed-Infected-Recovered (SEIR) model is developed with additional compartments for asymptomatic transmission. Further, a change-point is incorporated to model the before and after disease dynamics, and is inferred based on data. Related statistical analyses for inference are developed in a Bayesian framework and are able to provide quantitative assessments of (1) the impact of the Sri Petaling gathering, and (2) the extent of decreasing transmission during the MCO period. The analysis here also quantitatively demonstrates how quickly transmission rates fall under effective NPI implemention within a short time period.

scholarly journals The impact of AGN feedback on galaxy intrinsic alignments in the Horizon simulations

2020 ◽  
Vol 492 (3) ◽  
pp. 4268-4282 ◽  
Author(s):  
Adam Soussana ◽  
Nora Elisa Chisari ◽  
Sandrine Codis ◽  
Ricarda S Beckmann ◽  
Yohan Dubois ◽  
...  
Keyword(s):  
Galaxy Evolution ◽  
Gravitational Lensing ◽  
Large Scale ◽  
Galactic Nuclei ◽  
Three Dimensions ◽  
High Mass ◽  
Angular Momenta ◽  
The Galaxy ◽  
The Impact ◽  
The Universe

ABSTRACT The intrinsic correlations of galaxy shapes and orientations across the large-scale structure of the Universe are a known contaminant to weak gravitational lensing. They are known to be dependent on galaxy properties, such as their mass and morphologies. The complex interplay between alignments and the physical processes that drive galaxy evolution remains vastly unexplored. We assess the sensitivity of intrinsic alignments (shapes and angular momenta) to active galactic nuclei (AGN) feedback by comparing galaxy alignment in twin runs of the cosmological hydrodynamical Horizon simulation, which do and do not include AGN feedback, respectively. We measure intrinsic alignments in three dimensions and in projection at $z$ = 0 and $z$ = 1. We find that the projected alignment signal of all galaxies with resolved shapes with respect to the density field in the simulation is robust to AGN feedback, thus giving similar predictions for contamination to weak lensing. The relative alignment of galaxy shapes around galaxy positions is however significantly impacted, especially when considering high-mass ellipsoids. Using a sample of galaxy ‘twins’ across simulations, we determine that AGN changes both the galaxy selection and their actual alignments. Finally, we measure the alignments of angular momenta of galaxies with their nearest filament. Overall, these are more significant in the presence of AGN as a result of the higher abundance of massive pressure-supported galaxies.

scholarly journals A Nuclear Ring in the Sa(r!) Galaxy NGC 7742

1996 ◽  
Vol 157 ◽  
pp. 83-85 ◽  
Author(s):  
K. Wakamatsu ◽  
M. Hamabe ◽  
M. T. Nishida ◽  
A. Tomita
Keyword(s):  
Elliptical Galaxy ◽  
Formation Mechanisms ◽  
Main Body ◽  
Circular Symmetry ◽  
Barred Galaxies ◽  
Exclamation Mark ◽  
The Galaxy ◽  
Nuclear Ring ◽  
Lindblad Resonance ◽  
Inner Lindblad Resonance

NGC 7742 is well known for its prominent blue nuclear ring around an EO-like core, and so appears as a Hoag-type galaxy, an elliptical galaxy with an outer ring (Schweizer et al. 1987). The galaxy is classified as Sa(r!) in the Revised Shapley-Ames Catalog (Sandage and Tammann 1987) with an exclamation mark to emphasize the prominence of the ring. Its photographs are published in Laustsen et al. (1987), Wray (1988), and Sandage & Bedke (1994).The ring has a diameter of 19″ = 1.6 kpc at a distance of 17.1 Mpc (Buta & Crocker 1993), and so should be a nuclear ring of the galaxy. Nuclear rings and pseudorings are often detected in strongly barred (SB) galaxies, and interpreted to be linked to the inner Lindblad resonance (Buta & Crocker 1993). These nuclear features are, however, also found in some weakly-barred (SAB) and non-barred (SA) galaxies. NGC 7742 is a galaxy of the highest circular symmetry in its core, ring, and main body, and so the best object for a detailed study of formation mechanisms of nuclear rings in non-barred galaxies.

scholarly journals On the use of the WKBJ density wave theory at the Inner Lindblad Resonance region of our galaxy

1979 ◽  
Vol 84 ◽  
pp. 191-192
Author(s):  
E. Athanassoula
Keyword(s):  
Density Wave ◽  
Wave Theory ◽  
Resonance Region ◽  
Density Wave Theory ◽  
Lindblad Resonance ◽  
Inner Lindblad Resonance

I have tested the reliability of certain approximations involved in the asymptotic WKBJ density wave description of the inner Lindblad resonance (=ILR) of our galaxy.

Telomeres, telomerase, and apoptosis

2004 ◽  
Vol 82 (4) ◽  
pp. 498-507 ◽  
Author(s):  
Chiara Mondello ◽  
A Ivana Scovassi
Keyword(s):  
Cancer Cells ◽  
Telomerase Activity ◽  
Telomeric Dna ◽  
Apoptotic Response ◽  
Reverse Transcriptase Enzyme ◽  
Limited Life ◽  
Specific Proteins ◽  
Telomere Capping ◽  
The Impact ◽  
High Order Chromatin

Telomeres are specialized high-order chromatin structures that cap the ends of eukaryotic chromosomes. In vertebrates, telomeric DNA is composed of repetitions of the TTAGGG hexanucleotide, is bound to a set of specific proteins, and is elongated by the reverse transcriptase enzyme telomerase. Telomerase activity is promptly detected in cells with an indefinite replicative potential, such as cancer cells, while is almost undetectable in normal cells, which are characterized by a limited life span. Mounting evidence indicates that the maintenance of telomere integrity and telomerase protect cells from apoptosis. Disruption of the telomere capping function and (or) telomerase inhibition elicit an apoptotic response in cancer cells, while restoration of telomerase activity in somatic cells confers resistance to apoptosis. The possible mechanisms linking telomeres, telomerase and apoptosis are discussed in this review, together with the impact of this field in anticancer research.Key words: telomeres, telomerase, telomeric proteins, apoptosis, tumorigenesis.

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