Interaction of a cold cloud with a hot wind: the regimes of cloud growth and destruction and the impact of magnetic fields

ABSTRACT Multiphase galaxy winds, the accretion of cold gas through galaxy haloes, and gas stripping from jellyfish galaxies are examples of interactions between cold and hot gaseous phases. There are two important regimes in such systems. A sufficiently small cold cloud is destroyed by the hot wind as a result of Kelvin–Helmholtz instabilities, which shatter the cloud into small pieces that eventually mix and dissolve in the hot wind. In contrast, stripped cold gas from a large cloud mixes with the hot wind to intermediate temperatures, and then becomes thermally unstable and cools, causing a net accretion of hot gas to the cold tail. Using the magneto-hydrodynamical code arepo, we perform cloud crushing simulations and test analytical criteria for the transition between the growth and destruction regimes to clarify a current debate in the literature. We find that the hot-wind cooling time sets the transition radius and not the cooling time of the mixed phase. Magnetic fields modify the wind–cloud interaction. Draping of wind magnetic field enhances the field upstream of the cloud, and fluid instabilities are suppressed by a turbulently magnetized wind beyond what is seen for a wind with a uniform magnetic field. We furthermore predict jellyfish galaxies to have ordered magnetic fields aligned with their tails. We finally discuss how the results of idealized simulations can be used to provide input to subgrid models in cosmological (magneto-)hydrodynamical simulations, which cannot resolve the detailed small-scale structure of cold gas clouds in the circumgalactic medium.

A unified accretion-ejection paradigm for black hole X-ray binaries

Context. We proposed in paper I that the spectral evolution of transient X-ray binaries (XrB) is due to an interplay between two flows: a standard accretion disk (SAD) in the outer parts and a jet-emitting disk (JED) in the inner parts. We showed in papers II, III, and IV that the spectral evolution in X-ray and radio during the 2010–2011 outburst of GX 339-4 can be recovered. However, the observed variability in X-ray was never addressed in this framework. Aims. We investigate the presence of low frequency quasi-periodic oscillations (LFQPOs) during an X-ray outburst, and address the possible correlation between the frequencies of these LFQPOs and the transition radius between the two flows, rJ. Methods. We select X-ray and radio data that correspond to 3 outbursts of GX 339-4. We use the method detailed in Paper IV to obtain the best parameters rJ(t) and ṁin(t) for each outburst. We also independently search for X-ray QPOs in each selected spectra and compare the QPO frequency to the Kepler and epicyclic frequencies of the flow in rJ. Results. We successfully reproduce the correlated evolution of the X-ray spectra and the radio emission for 3 different activity cycles of GX 339-4. We use a unique normalisation factor for the radio emission, f∼R. We also report the detection of 7 new LFQPOs (3 Type B, and 4 Type C), to go along with the ones previously reported in the literature. We show that the frequency of Type C QPOs can be linked to the dynamical JED-SAD transition radius rJ, rather than to the optically thin-thick transition radius in the disk. The scaling factor q such that νQPO ≃ νK(rJ)/q is q ≃ 70 − 130, a factor consistent during the 4 cycles, and similar to previous studies. Conclusions. The JED-SAD hybrid disk configuration not only provides a successful paradigm allowing us to describe XrB cycles, but also matches the evolution of QPO frequencies. Type C QPOs provide an indirect way to probe the JED-SAD transition radius, where an undetermined process produces secular variability. The demonstrated relation between the transition radius links Type C QPOs to the transition between two different flows, effectively tying it to the inner magnetized structure, i.e., the jets. This direct connection between the jets’ (accretion-ejection) structure and the process responsible for Type C QPOs, if confirmed, could naturally explain their puzzling multi-wavelength behavior.

Напряженное состояние полимерных покрытий судовых конструкций переменной жесткости

Полимерные покрытия являются эффективным инструментом решения задач ремонта судовых корпусных конструкций без нарушения их целостности. Они служат альтернативой ремонту методом замены. Поэтому расчет прочностных показателей полимерных покрытий судовых конструкций является актуальной задачей. Особенно важно иметь алгоритмы расчета прочности для конструкций переменной жесткости. Проведены исследования полей напряжений армированных полимерных покрытий на границах изменения жесткости судовых конструктивных элементов. Целью работ являлось раскрытие механизма отслоения покрытия, создание надежных экспериментальных методик. Принята гипотеза о постоянстве по толщине покрытия напряжений, действующих параллельно границе раздела композиции металл-покрытие. Считается, что жесткость покрытия значительно меньше, чем у металла, деформация композиции металл-покрытие подчиняется закону плоских сечений. Приведен пример аппроксимации реального перехода от одной толщины к другой в виде галтели. Представлены распределение нормальных и касательных напряжений по длине переходного участка, зависимость максимальных значений нормальных и касательных напряжений от радиуса перехода. Установлено, что изменение жесткости судового конструктивного элемента приводит к локальному изменению поля напряжений в армированном полимерном покрытии и появлению в этой зоне дополнительных напряжений.Polymer coatings are an effective tool for solving the problems of repair of ship hull structures without violating their integrity. They serve as an alternative to repair by replacement method. Therefore, the calculation of strength indicators of polymer coatings of ship structures is an urgent task. It is especially important to have strength calculation algorithms for variable stiffness structures. Stress fields of reinforced polymer coatings on the boundaries of changes in the stiffness of ship structural elements were studied. The aim of the work was to reveal the mechanism of coating detachment, the creation of reliable experimental techniques. The hypothesis of the constancy of the coating thickness stresses acting parallel to the interface of the composition metal-coating. It is believed that the stiffness of the coating is much less than that of the metal, the deformation of the metal-coating composition obeys the law of flat sections. An example of approximation of the real transition from one thickness to another in the form of a galtel is given. The distribution of normal and tangential stresses along the length of the transition section, the dependence of the maximum values of normal and tangential stresses on the transition radius are presented. It is established that the change in the rigidity of the ship structural element leads to a local change in the stress field in the reinforced polymer coating and the appearance of additional stresses in this zone.

Elliptical galaxies/stellar halos connection

Cosmological simulations predict that early-type galaxies (ETGs) are the results of extended mass accretion histories. The latter are characterized by different numbers of mergers, mergers’ mass ratios and gas fractions, and timing. Depending on the sequence and nature of these mergers that follow the first phase of the in-situ star formation, these accretion histories may lead to ETGs that have low or high mass halos, and that rotate fast or slow. Since the stellar halos maintain the fossil records of the events that led to their formation, a discontinuity may be in place between the inner regions of ETGs and their outer halos, because the time required for the halos’ stars to exchange their energies and momenta is very long compared with the age of these systems. Exquisite deep photometry and extended spectroscopy for significant samples of ETGs are then used to quantify the occurrence and significance of such a transition in the galaxies’ structural and kinematical parameters. Once this transition radius is measured, its dependency with the effective radius of the galaxies’ light distribution and total stellar masses can be investigated. Such correlations can then be compared with the predictions of accreted, i.e. ex-situ vs. in-situ components from cosmological simulations to validate such models.

A unified accretion-ejection paradigm for black hole X-ray binaries

Context. It has been suggested that the cycles of activity of X-ray binaries (XRB) are triggered by a switch in the dominant disk torque responsible for accretion. As the disk accretion rate increases, the disk innermost regions therefore change from a jet-emitting disk (JED) to a standard accretion disk (SAD). Aims. While JEDs have been proven to successfully reproduce X-ray binary hard states, the existence of an outer cold SAD introduces an extra nonlocal cooling term. We investigate the thermal structure and associated spectra of such a hybrid disk configuration. Methods. We use a two-temperature plasma code, allowing for outside-in computation of the disk local thermal equilibrium with self-consistent advection and optically thin-to-thick transitions in both radiation and gas supported regimes. The nonlocal inverse Compton cooling introduced by the external soft photons is computed by the BELM code. Results. This additional cooling term has a profound influence on JED solutions, allowing a smooth temperature transition from the outer SAD to the inner JED. We explore the full parameter space in disk accretion rate and transition radius, and show that the whole domain in X-ray luminosities and hardness ratios covered by standard XRB cycles is well reproduced by such hybrid disk configurations. Precisely, a reasonable combination of these parameters allows us to reproduce the 3–200 keV spectra of each of five canonical XRB states. Along with these X-ray signatures, JED-SAD configurations also naturally account for the radio emission whenever it is observed. Conclusions. By varying only the radial transition radius and the accretion rate, hybrid disk configurations combining an inner JED and an outer SAD are able to simultaneously reproduce the X-ray spectral states and radio emission of X-ray binaries during their outburst. Adjusting these two parameters, it is then possible to reproduce a full cycle. This will be shown in a forthcoming paper.

TRANSFORMATION AND SCATTERING OF SURFACE WAVES ON THE ACOUSTIC LOAD TO ULTRASONIC EVALUATION AND MEASUREMENTS. Part 2. The object to study – solid with ledge

The lack of information about the features of processes of the surface wave's transformation into volume waves and its scattering in metal objects with ledge, slots, grooves and the others is one of the obstacles to improve of the acoustical testing reliability and widening of technical application. The aim of this work was to study of mechanism of acoustical mode's transformation and determination the laws of the fields forming of scatted volume edge wave's in solids with ledge of different geometry and to suggest direction of the study application in area of acoustical testing and measurements.The features of transformation of surface waves into edge transverse and longitudinal wave modes scatted and their fields forming in the volume of the object with ledge vs. its angle of the slope front surface side (0–135°) and a dimensionless transition radius (0–10,2) varied were studied. Theoretical analysis and experimental data shown that in general case the field of the edge transverse waves in the volume of ledge can be imagined as a superposition of the field of edge waves (scatted on ledge) and accompany waves too, radiated simultaneously with the surface waves to radiate. If dimensionless size of the ledge's transition radius lesser than 1 the resulting field of the edge transverse waves is the summary field of two sources. One of them (with small aperture) is localized in the vicinity of the place of intersection of contact surface with ledge's front side surface. As it was found, the second source of the edge transverse waves – the edge head longitudinal waves to appear in the results of transformation of surface waves on the ledge′s radius transition. The structure of the edge acoustic fields including their extremes vs. ledge's angle and its radius transition, position of the surface wave's probe were experimentally studied and theoretically analyzed.Some directions of the results of researches using are the next: а) ultrasonic testing of hard-to-make technological objects in which defects have low sound reflection; b) ultrasonic structure diagnostics of solid (specimens) set far from the ultrasonic by using edge volume transverse and longitudinal modes; c) creation of new ultrasonic arrangements to sound and to receive transverse waves of different polarization.

Optimization of Forging Process Parameters and Anvil Design for Railway Axle During High-Speed Forging

Forging is an effective method for railway axle in order to ensure the inner quality, good microstructure and properties. Based on the disadvantage of current processing techniques for railway axle forging such as large machining allowance, low dimension accuracy, materials and energy consumption, a new precision high-speed forging forming process is proposed. The whole forging process of axle is divided into three steps, including chamfering, rounding and forming. Forming qualities of railway axle mainly depend on anvil structure and operational parameters during high-speed forging. Simulation model is established using finite element method by DEFORM. Focusing on the forging stage of the railway axles, the influences of anvil design have been numerically analyzed. By analyzing the stress-strain distribution and the forming precision with different anvil structures (flat anvil and arc anvil), a new arc anvil for axle forging is proposed. Arc anvil which we put forward is better than flat anvil both forming quality and properties. As for anvil edge shape design, it is effective to select a Per-form zone to obtain high strain at the center. Structure and main parameters are designed. Effect of anvil relative length, transition radius between Per-form zone and relative length, arc radius of arc anvil on forming quality is analyzed in term of surface defects and inner stress-strain distribution. While the radius of arc is 150mm and the central angle of the arc is 90°, the equivalent strain is greater which will be benefit for inner defects cogging. Transition radius between Per-form zone and relative length is 50mm, concave defects on the surface of forging is the smaller. With the increase of relative length, forging force increases. Taking the productivity and inner strain distribution into account, relative length is 240mm. The independent influence of each chosen major operational parameter, i.e, the rotation angle, the feed and the reduction on internal quality and dimensional precision, has been studied. Suitable operational parameters for ensuring internal quality and dimensional precision have been specified. As a result, the optimum combination of rotational angle and relative feed is clarified. Compared with stress-strain distribution and inner strain distribution under different reduction, 20% is taken to ensure better strain status and efficiency, rotation angle is 90°during chamfering. While the relative feed is 0.6, rotation angle is 45° during rounding, rounding precision will be higher. Ellipticity will be best and variance of radius will be small. Experiment research is performed in 10MN high-speed hydraulic press. Compared with the forming size precision, the experimental results verified the feasibility of the structure of arc anvil and the operational parameters.

Numerical Simulation of Screw Manufacturing Process for the Assessment of Surface Integrity

Stress corrosion cracks have been observed on screws made of stainless steels grade 316 after some years of service in Pressurized Water Reactor (PWR) water environment. Grade 316 of stainless steel is not sensitive to corrosion unless it has been sensitized and/or subjected to a complex combination of factors including an important level cold work at the surface and in the bulk of the material. The tightening of the screw induces tensile stresses. This preload cannot explain the Stress Corrosion Cracking (SCC) defect appearing in the transition radius between the screw shank and its head. Thus, the question has been raised of the initial state of the screws after manufacturing. The simulation of the manufacturing processes has been carried out to have a better understanding of manufacturing process consequences on material degradation: solution annealing, cold drawing and machining. The dedicated “hybrid method”, specifically set up to simulate finish turning has been applied to obtain stress and strain states close to the surface. This method is detailed in the paper. The manufacturing process of these bolts is likely to induce high strain hardening since they have been cold drawn and then machined. It is suspected that tensile residual stress and cold work play a major role in the initiation of stress corrosion cracking of austenitic stainless steel grade of 316 type in PWR water environment. Simulation chaining method and results are highlighted in the paper with comparison with experiments. The main achievements are: the smaller the screw the less the cold work, the residual stress on the surface is mainly due to machining and the location of crack in the transition radius is well explained.