JET STABILITY, DYNAMICS AND ENERGY TRANSPORT

Relativistic jets carry energy and particles from compact to very large scales compared with their initial radius. This is possible due to their remarkable collimation despite their intrinsic unstable nature. In this contribution, I review the state-of-the-art of our knowledge on instabilities growing in those jets and several stabilising mechanisms that may give an answer to the question of the stability of jets. In particular, during the last years we have learned that the limit imposed by the speed of light sets a maximum amplitude to the instabilities, contrary to the case of classical jets. On top of this stabilising mechanism, the fast growth of unstable modes with small wavelengths prevents the total disruption and entrainment of jets. I also review several non-linear processes that can have an effect on the collimation of extragalactic and microquasar jets. Within those, I remark possible causes for the decollimation and deceleration of FRI jets, as opposed to the collimated FRII's. Finally, I give a summary of the main reasons why jets can propagate through such long distances.

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Quantum-mechanical hydration plays critical role in the stability of firefly oxyluciferin isomers: State-of-the-art calculations of the excited states

The Journal of Chemical Physics ◽

10.1063/5.0031356 ◽

2020 ◽

Vol 153 (20) ◽

pp. 201103

Author(s):

Yoshifumi Noguchi ◽

Miyabi Hiyama ◽

Motoyuki Shiga ◽

Hidefumi Akiyama ◽

Osamu Sugino

Keyword(s):

Excited States ◽

State Of The Art ◽

Critical Role ◽

Quantum Mechanical ◽

The Stability

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On the relation between mini-halos and AGN feedback in clusters of galaxies

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa2877 ◽

2020 ◽

Vol 499 (2) ◽

pp. 2934-2958

Author(s):

A Richard-Laferrière ◽

J Hlavacek-Larrondo ◽

R S Nemmen ◽

C L Rhea ◽

G B Taylor ◽

...

Keyword(s):

Large Scale ◽

State Of The Art ◽

Vital Role ◽

Clusters Of Galaxies ◽

Relativistic Jets ◽

X Ray ◽

Core Cluster ◽

Central Galaxy ◽

Central Regions ◽

Radio Power

ABSTRACT A variety of large-scale diffuse radio structures have been identified in many clusters with the advent of new state-of-the-art facilities in radio astronomy. Among these diffuse radio structures, radio mini-halos are found in the central regions of cool core clusters. Their origin is still unknown and they are challenging to discover; less than 30 have been published to date. Based on new VLA observations, we confirmed the mini-halo in the massive strong cool core cluster PKS 0745−191 (z = 0.1028) and discovered one in the massive cool core cluster MACS J1447.4+0827 (z = 0.3755). Furthermore, using a detailed analysis of all known mini-halos, we explore the relation between mini-halos and active galactic nucleus (AGN) feedback processes from the central galaxy. We find evidence of strong, previously unknown correlations between mini-halo radio power and X-ray cavity power, and between mini-halo and the central galaxy radio power related to the relativistic jets when spectrally decomposing the AGN radio emission into a component for past outbursts and one for ongoing accretion. Overall, our study indicates that mini-halos are directly connected to the central AGN in clusters, following previous suppositions. We hypothesize that AGN feedback may be one of the dominant mechanisms giving rise to mini-halos by injecting energy into the intra-cluster medium and reaccelerating an old population of particles, while sloshing motion may drive the overall shape of mini-halos inside cold fronts. AGN feedback may therefore not only play a vital role in offsetting cooling in cool core clusters, but may also play a fundamental role in re-energizing non-thermal particles in clusters.

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Numerical Investigation of the Solidity Effect on Linear Compressor Cascades

Volume 2A: Turbomachinery ◽

10.1115/gt2014-25532 ◽

2014 ◽

Cited By ~ 1

Author(s):

J. Sans ◽

M. Resmini ◽

J.-F. Brouckaert ◽

S. Hiernaux

Keyword(s):

Numerical Investigation ◽

State Of The Art ◽

Leading Edge ◽

Operating Conditions ◽

Compressor Cascade ◽

Minimum Loss ◽

Low Speed ◽

High Mach ◽

The Stability ◽

The Impact

Solidity in compressors is defined as the ratio of the aerodynamic chord over the peripheral distance between two adjacent blades, the pitch. This parameter is simply the inverse of the pitch-to-chord ratio generally used in turbines. Solidity must be selected at the earliest design phase, i.e. at the level of the meridional design and represents a crucial step in the whole design process. Most of the existing studies on this topic rely on low-speed compressor cascade correlations from Carter or Lieblein. The aim of this work is to update those correlations for state-of-the-art controlled diffusion blades, and extend their application to high Mach number flow regimes more typical of modern compressors. Another objective is also to improve the physical understanding of the solidity effect on compressor performance and stability. A numerical investigation has been performed using the commercial software FINE/Turbo. Two different blade profiles were selected and investigated in the compressible flow regime as an extension to the low-speed data on which the correlations are based. The first cascade uses a standard double circular arc profile, extensively referenced in the literature, while the second configuration uses a state-of-the-art CDB, representative of low pressure compressor stator mid-span profile. Both profiles have been designed with the same inlet and outlet metal angles and the same maximum thickness but the camber and thickness distributions, the stagger angle and the leading edge geometry of the CDB have been optimized. The determination of minimum loss, optimum incidence and deviation is addressed and compared with existing correlations for both configurations and various Mach numbers that have been selected in order to match typical booster stall and choke operating conditions. The emphasis is set on the minimum loss performance at mid-span. The impact of the solidity on the operating range and the stability of the cascade are also studied.

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Temperature Effects on Optical Trapping Stability

Micromachines ◽

10.3390/mi12080954 ◽

2021 ◽

Vol 12 (8) ◽

pp. 954

Author(s):

Dasheng Lu ◽

Francisco Gámez ◽

Patricia Haro-González

Keyword(s):

Brownian Motion ◽

Environmental Conditions ◽

Temperature Effects ◽

Room Temperature ◽

Optical Trapping ◽

State Of The Art ◽

Thermal Sensing ◽

The Stability ◽

Object Of Study ◽

Optically Trapped

In recent years, optically trapped luminescent particles have emerged as a reliable probe for contactless thermal sensing because of the dependence of their luminescence on environmental conditions. Although the temperature effect in the optical trapping stability has not always been the object of study, the optical trapping of micro/nanoparticles above room temperature is hindered by disturbances caused by temperature increments of even a few degrees in the Brownian motion that may lead to the release of the particle from the trap. In this report, we summarize recent experimental results on thermal sensing experiments in which micro/nanoparticles are used as probes with the aim of providing the contemporary state of the art about temperature effects in the stability of potential trapping processes.

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THE INFLUENCES OF TEMPERATURE AND CHAIN–CHAIN INTERACTION ON FEATURES OF SOLITONS EXCITED IN α-HELIX PROTEIN MOLECULES WITH THREE CHANNELS

International Journal of Modern Physics B ◽

10.1142/s0217979209052546 ◽

2009 ◽

Vol 23 (10) ◽

pp. 2303-2322 ◽

Cited By ~ 6

Author(s):

XIAO-FENG PANG ◽

MEI-JIE LIU

Keyword(s):

Energy Transport ◽

Initial Conditions ◽

Dynamic Features ◽

New Model ◽

Protein Molecules ◽

Long Time ◽

The Stability ◽

Α Helix ◽

Increasing Temperature ◽

Chain Interaction

The dynamic features of soliton transporting the bio-energy in the α-helix protein molecules with three channels under influences of temperature of systems and chain–chain interaction among these channels have been numerically studied by using the dynamic equations in a new model and the fourth-order Runge–Kutta method. This result obtained shows that the chain–chain interaction depresses the stability of the soliton due to the dispersed effect, but the stability of the soliton in the case of simultaneous motivation of three channels by an initial conditions is better than that in another initial condition. We also find from this investigation that the new soliton can transport steadily over 1000 amino acid residues in the cases of motion of long time of 120 ps, and retain their shapes and energies to travel towards the protein molecules after mutual collision of the solitons at the biological temperatures of 300 K. Therefore the soliton is very robust against the thermal perturbation of the α-helix protein molecules at 300 K. From the investigation of changes of features of the soliton with increasing temperature, we find that the amplitudes and velocities of the solitons decrease with increasing temperature of proteins, but the soliton disperses in the cases of higher temperature of 325 K and larger structure disorders. Thus we find that the critical temperature of the soliton occurring in the α-helix protein molecules is about 320 K. Therefore we can conclude that the soliton in the new model can play an important role in the bio-energy transport in the α-helix protein molecules with three channels at biological temperature, and the new model is possibly a candidate for the mechanism of this transport.

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The Stability-Limiting Flow Mechanisms in a Subsonic Axial-Flow Compressor and Its Passive Control With Casing Treatment

Volume 6: Turbomachinery, Parts A, B, and C ◽

10.1115/gt2008-50006 ◽

2008 ◽

Cited By ~ 2

Author(s):

Xingen Lu ◽

Junqiang Zhu ◽

Chaoqun Nie ◽

Weiguang Huang

Keyword(s):

Flow Instability ◽

State Of The Art ◽

Axial Flow ◽

Flow Mechanism ◽

Blade Passage ◽

Casing Treatment ◽

Compressor Rotor ◽

Flow Compressor ◽

The Stability ◽

End Wall

The phenomenon of flow instability in the compression system such as fan and compressor has been a long-standing “bottle-neck” problem for gas turbines/aircraft engines. With a vision of providing a state-of-the-art understanding of the flow field in axial-flow compressor in the perspective of enhancing their stability using passive means. Two topics are covered in this paper. The first topic is the stability-limiting flow mechanism close to stall, which is the basic knowledge needed to manipulate end-wall flow behavior for the stability improvement. The physical process occurring when approaching stall and the role of complex tip flow mechanism on flow instability in current high subsonic axial compressor rotor has been assessed using single blade passage computations. The second topic is flow instability manipulation with casing treatment. In order to advance the understanding of the fundamental mechanisms of casing treatment and determine the change in the flow field by which casing treatment improve compressor stability, systematic studies of the coupled flow through a subsonic compressor rotor and various end-wall treatments were carried out using a state-of-the-art multi-block flow solver. The numerically obtained flow fields were interrogated to identify complicated flow phenomenon around and within the end-wall treatments and describe the interaction between the rotor tip flow and end-wall treatments. Detailed analyses of the flow visualization at the rotor tip have exposed the different tip flow topologies between the cases with treatment casing and with untreated smooth wall. It was found that the primary stall margin enhancement afforded by end-wall treatments is a result of the tip flow manipulation. Compared to the smooth wall case, the treated casing significantly dampen or absorb the blockage near the upstream part of the blade passage caused by the upstream movement of tip clearance flow and weakens the roll-up of the core vortex. These mechanisms prevent an early spillage of low momentum fluid into the adjacent blade passage and delay the onset of flow instability.

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An interior solution with perfect fluid

Modern Physics Letters A ◽

10.1142/s0217732320501412 ◽

2020 ◽

Vol 35 (17) ◽

pp. 2050141 ◽

Cited By ~ 1

Author(s):

Joaquin Estevez-Delgado ◽

Jose Vega Cabrera ◽

Joel Arturo Rodriguez Ceballos ◽

Arthur Cleary-Balderas ◽

Mauricio Paulin-Fuentes

Keyword(s):

Perfect Fluid ◽

Speed Of Sound ◽

Numerical Data ◽

Index Formula ◽

Interior Solution ◽

Radial Coordinate ◽

Speed Of Light ◽

Bounded Functions ◽

The Stability ◽

Stability Of The Solution

Starting from the construction of a solution for Einstein’s equations with a perfect fluid for a static spherically symmetric spacetime, we present a model for stars with a compactness rate of [Formula: see text]. The model is physically acceptable, that is to say, its geometry is non-singular and does not have an event horizon, pressure and speed of sound are bounded functions, positive and monotonically decreasing as function of the radial coordinate, also the speed of sound is lower than the speed of light. While it is shown that the adiabatic index [Formula: see text], which guarantees the stability of the solution. In a complementary manner, numerical data are presented considering the star PSR J0737-3039A with observational mass of [Formula: see text], for the value of compactness [Formula: see text], which implies the radius [Formula: see text] and the range of the density [Formula: see text] [Formula: see text], where [Formula: see text] and [Formula: see text] are the central density and the surface density, respectively. This range is consistent with the expected values; as such, the model presented allows to describe this type of stars.

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Fast and Deep Graph Neural Networks

Proceedings of the AAAI Conference on Artificial Intelligence ◽

10.1609/aaai.v34i04.5803 ◽

2020 ◽

Vol 34 (04) ◽

pp. 3898-3905 ◽

Cited By ~ 4

Author(s):

Claudio Gallicchio ◽

Alessio Micheli

Keyword(s):

Neural Network ◽

Dynamical System ◽

Neural Networks ◽

State Of The Art ◽

Input Graph ◽

Sparse Networks ◽

Set Up ◽

The Stability ◽

Graph Neural Networks ◽

Architectural Organization

We address the efficiency issue for the construction of a deep graph neural network (GNN). The approach exploits the idea of representing each input graph as a fixed point of a dynamical system (implemented through a recurrent neural network), and leverages a deep architectural organization of the recurrent units. Efficiency is gained by many aspects, including the use of small and very sparse networks, where the weights of the recurrent units are left untrained under the stability condition introduced in this work. This can be viewed as a way to study the intrinsic power of the architecture of a deep GNN, and also to provide insights for the set-up of more complex fully-trained models. Through experimental results, we show that even without training of the recurrent connections, the architecture of small deep GNN is surprisingly able to achieve or improve the state-of-the-art performance on a significant set of tasks in the field of graphs classification.

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Stability of Fractional Order Systems

Mathematical Problems in Engineering ◽

10.1155/2013/356215 ◽

2013 ◽

Vol 2013 ◽

pp. 1-14 ◽

Cited By ~ 57

Author(s):

Margarita Rivero ◽

Sergei V. Rogosin ◽

José A. Tenreiro Machado ◽

Juan J. Trujillo

Keyword(s):

Fractional Calculus ◽

Fractional Order ◽

State Of The Art ◽

Point Of View ◽

Fractional Order Systems ◽

Short Period ◽

Systems And Control ◽

Different Types ◽

The Stability ◽

And Control

The theory and applications of fractional calculus (FC) had a considerable progress during the last years. Dynamical systems and control are one of the most active areas, and several authors focused on the stability of fractional order systems. Nevertheless, due to the multitude of efforts in a short period of time, contributions are scattered along the literature, and it becomes difficult for researchers to have a complete and systematic picture of the present day knowledge. This paper is an attempt to overcome this situation by reviewing the state of the art and putting this topic in a systematic form. While the problem is formulated with rigour, from the mathematical point of view, the exposition intends to be easy to read by the applied researchers. Different types of systems are considered, namely, linear/nonlinear, positive, with delay, distributed, and continuous/discrete. Several possible routes of future progress that emerge are also tackled.

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