Jet Speed Research Articles

Discovery of a bright extended X-ray jet in RGB J1512+020A

ABSTRACTWe report the discovery of a bright, extended X-ray jet in the quasar RGB J1512+020A (z = 0.22). Chandra observations show the X-ray core and 13 arcsec (∼45 kpc projected) extended emission coincident with the radio jet. The jet stands out as one of brightest X-ray jets (LX ∼ 7 × 1043 erg s−1) at low redshift (z < 0.5) discovered so far, with remarkably large X-ray to radio luminosity ratios (LX/Lr up to ∼50). We identified four main components, two unresolved knots and two extended structures, one being the jet brightest feature (JBF). All jet features are also detected in ALMA archival observations. The radio, sub-mm to X-ray spectra of the two knots can be modelled with a single synchrotron component. For the two resolved structures, the ALMA data unveil a turnover of the low-energy continuum at ∼460 GHz. External Comptonization of cosmic microwave background photons can account for the observed X-ray emission if the jet speed remains highly relativistic, with bulk motion Γbulk > 15, up to tens of kiloparsec from the core. However, the comparison with the spectral energy distribution of similar X-ray detected jets shows that the alternative hypothesis of synchrotron emission from an additional population of ultra-high-energy electrons is also possible. We report a tentative (≳2σ) optical detection of the JBF in images of the Dark Energy Camera Legacy Survey. If confirmed, the optical emission should be either the low-energy tail of the radiative component responsible for the X-ray emission or a third, separate component.

A regional (land–ocean) comparison of the seasonal to decadal variability of the Northern Hemisphere jet stream 1871–2011

Seasonal to decadal variations in Northern Hemisphere jet stream latitude and speed over land (Eurasia, North America) and oceanic (North Atlantic, North Pacific) regions are presented for the period 1871–2011 from the Twentieth Century Reanalysis dataset. Significant regional differences are seen on seasonal to decadal timescales. Seasonally, the jet latitude range is lower over the oceans compared to land, reduced from 20° over Eurasia to 10° over the North Atlantic where the ocean meridional heat transport is greatest. The mean jet latitude range is at a minimum in winter (DJF), particularly along the western boundary of the North Pacific and North Atlantic, where the land-sea contrast and SST gradients are strongest. The 141-year trends in jet latitude and speed show differences on a regional basis. The North Atlantic has significant increasing jet latitude trends in all seasons, up to 3° in winter. Eurasia has significant increasing trends in winter and summer, however, no increase is seen across the North Pacific or North America. Jet speed shows significant increases evident in winter (up to 4.7 ms−1), spring and autumn over the North Atlantic, Eurasia and North America however, over the North Pacific no increase is observed. Long term trends are generally overlaid by multidecadal variability, particularly evident in the North Pacific, where 20-year variability in jet latitude and jet speed are seen, associated with the Pacific Decadal Oscillation which explains 50% of the winter variance in jet latitude since 1940. The results highlight that northern hemisphere jet variability and trends differ on a regional basis (North Atlantic, North Pacific, Eurasia and North America) on seasonal to decadal timescales, suggesting that different mechanisms are influencing the jet latitude and speed. This is important from a climate modelling perspective and for climate predictions in the near and longer term.

Energetics of Transient Eddies Related to the Midwinter Minimum of the North Pacific Storm-Track Activity

Abstract Storm-track activity over the North Pacific (NP) climatologically exhibits a clear minimum in midwinter, when the westerly jet speed sharply maximizes. This counterintuitive phenomenon, referred to as the “midwinter minimum (MWM),” has been investigated from various perspectives, but the mechanisms are still to be unrevealed. Toward better understanding of this phenomenon, the present study delineates the detailed seasonal evolution of climatological-mean Eulerian statistics and energetics of migratory eddies along the NP storm track over 60 years. As a comprehensive investigation of the mechanisms for the MWM, this study has revealed that the net eddy conversion/generation rate normalized by the eddy total energy, which is independent of eddy amplitude, is indeed reduced in midwinter. The reduction from early winter occurs mainly due to the decreased effectiveness of the baroclinic energy conversion through seasonally weakened temperature fluctuations and the resultant poleward eddy heat flux. The reduced net normalized conversion/generation rate in midwinter is also found to arise in part from the seasonally enhanced kinetic energy conversion from eddies into the strongly diffluent Pacific jet around its exit. The seasonality of the net energy influx also contributes especially to the spring recovery of the net normalized conversion/generation rate. The midwinter reduction in the normalized rates of both the net energy conversion/generation and baroclinic energy conversion was more pronounced in the period before the late 1980s, during which the MWM of the storm-track activity was climatologically more prominent.

Numerical dissipation strongly affects the equatorial jet speed in simulations of hot Jupiter atmospheres

ABSTRACT Hot Jupiters are tidally locked gaseous exoplanets with atmospheric circulations dominated by a super-rotating equatorial jet. Their global circulation is often studied with simulations in 3D general circulation models (GCMs). Energy builds up at the smallest scales in these models and must be dissipated. Many models use ‘hyperdiffusion’ for this, which applies a tendency to the prognostic variables based on a high-order Laplacian operator. This removes the unrealistic and unstable build-up of energy at small scales, and ideally does not affect the large-scale circulation. In this study, we show that hyperdiffusion can in fact affect the large-scale circulation of simulations of hot Jupiters. These planets have large velocity gradients, so hyperdiffusion can produce a momentum tendency that may affect the largest scales. We analyse four simulations with different hyperdiffusion parameters in the GCM THOR. These show that hyperdiffusion can affect the atmospheric zonal momentum budget as strongly as the physical forcing. The hyperdiffusion slows down and spreads out the jet, reducing its speed by more than $50{{\ \rm per\ cent}}$ at some levels. We analyse simulations from the GCMs MITgcm and Exo-FMS and compare the effects of their different dissipation methods. The drag on the jet due to hyperdiffusion can be reduced by using a weaker hyperdiffusion coefficient, a higher resolution, or higher order diffusion. We aim to provide a basis for a study to investigate the ‘real’ momentum budget and jet speed of hot Jupiters. This study shows the need to examine long-held modelling assumptions when studying novel exoplanets.

A compact symmetric radio source born at one-tenth the current age of the Universe

ABSTRACT Studies of high-redshift radio galaxies can shed light on the activity of active galactic nuclei (AGNs) in massive elliptical galaxies, and on the assembly and evolution of galaxy clusters in the Universe. J1606+3124 has been tentatively identified as a radio galaxy at a redshift of 4.56, at an era of one-tenth of the current age of the Universe. Very long baseline interferometry (VLBI) images show a compact triple structure with a size of 68 pc. The radio properties of J1606+3124, including the edge-brightening morphology, peaked GHz radio spectrum, slow variability, and low jet speed, consistently indicate that it is a compact symmetric object (CSO). The radio source size and expansion rate of the hotspots suggest that J1606+3124 is a young (kinematic age of ∼3600 yr) radio source. Infrared observations reveal a gas- and dust-rich host galaxy environment, which may hinder the growth of the jet; however, the ultra-high jet power of J1606+3124 gives it an excellent chance to grow into a large-scale double-lobe radio galaxy. If its redshift and galaxy classification can be confirmed by further optical spectroscopic observations, J1606+3124 will be the highest redshift CSO galaxy known to date.

A Novel Theoretical Model Development and Simulation of Melt‐Electrospinning Using Kane's and Udwadia–Kalaba Methods

AbstractA novel analytical model development and simulation of melt‐electrospinning process is presented. Unconstrained equations of motion for the description of a discretized melt‐electrospun fiber are formulated using Kane's method. The motions of the spinneret and the collector plate are also incorporated into the kinematics formulation to simulate direct writing and three‐dimensional printing scenarios. Constraints describing viscoelastic joints in the system and the phenomenon of the melt‐electrospun fiber adhering to the collector plate are implemented using the Udwadia Kalaba method. Rotational viscoelastic elements are introduced to mimic the dampening of the whipping motion observed in the unstable region. A novel algorithm is devised to continuously run the simulation with no limit on the total duration and phase transitions. System responses such as fiber diameter, collection size, fiber elongations, and jet speeds are monitored for changes in control parameters including applied voltage, collector distance, and flowrate. The results demonstrate close agreement with experimental observations in the literature. The jet starts relatively straight on the onset of its trajectory and develops subtle whipping motion as it advances toward the collector plate. Reduction in the amplitude of the whipping motion is observed once the free end of the fiber adhered to the collector plate.

Processing of Poly(lactic‐co‐glycolic acid) Microfibers via Melt Electrowriting

AbstractPolymers sensitive to thermal degradation include poly(lactic‐co‐glycolic acid) (PLGA), which is not yet processed via melt electrowriting (MEW). After an initial period of instability where mean fiber diameters increase from 20.56 to 27.37 µm in 3.5 h, processing stabilizes through to 24 h. The jet speed, determined using critical translation speed measurements, also reduces slightly in this 3.5 h period from 500 to 433 mm min−1 but generally remains constant. Acetyl triethyl citrate (ATEC) as an additive decreases the glass transition temperature of PLGA from 49 to 4 °C, and the printed ATEC/PLGA fibers exhibits elastomeric behavior upon handling. Fiber bundles tested in cyclic mechanical testing display increased elasticity with increasing ATEC concentration. The processing temperature of PLGA also reduces from 165 to 143 °C with increase in ATEC concentration. This initial window of unstable direct writing seen with neat PLGA can also be impacted through the addition of 10‐wt% ATEC, producing fiber diameters of 14.13 ± 1.69 µm for the first 3.5 h of heating. The investigation shows that the initial changes to the PLGA direct‐writing outcomes seen in the first 3.5 h are temporary and that longer times result in a more stable MEW process.

Study on liquid nitrogen and carbon dioxide combined jet quick-frozen strawberry

According to the phase change property of carbon dioxide and the rapid cooling ability of liquid nitrogen, an experimental system of quick-frozen strawberry by combined jet of carbon dioxide and liquid nitrogen was designed. Through a series of experiments, the pressure changes and jet outlet temperature at different nitrogen jet speeds at different temperatures were studied. Then, the effects of nitrogen injection speed at different low temperatures and different inlet positions in the quick-frozen room on the quick-frozen strawberry freezing rate was investigated. The final results show that when the jet speed of low-temperature nitrogen increases, the pressure loss in the flow process also increases gradually. At the same time, the speed of mixing will increase, and the disturbance will increase, and the outlet jet temperature will also decrease. When the nitrogen inlet speed was 0.2 m/s, the temperature between the strawberry was uniform. Different inlet and outlet positions had no influence on the freezing time of strawberry. Quick-freezing room (c) improves the heat transfer efficiency and makes the temperature of strawberries more uniform. The results obtained lay a foundation for further research and development of an efficient quick-frozen product device.

Processing of flat glass

The article discusses the issues of sheet glass processing and provides information about the application, advantages, disadvantages and technological capabilities. The technological parameters of waterjet processing that affect to the cutting quality: the jet speed, the grain size of the abrasive, the angle of jet inclination, the distance from the nozzle to the treated surface. The water cutting method or waterjet cutting can significantly increase the speed and quality of material cutting. From an economic point of view, the consumption of material and energy is significantly reduced (by 20-30%), due to the use of water energy as the cutting tool in this method. The consumable material is only water and abrasive material. By modeling, when using software, it is proved that during waterjet cutting, lower stresses are formed in the glass compared to mechanical roller cutting, thereby ensuring minimal heat generation and accurate cutting with an edge roughness of Ra 1.6 microns.

An experimental and numerical study on the modelling of fluid flow, heat transfer and solidification in a copper continuous strip casting process

An experimental and “numerical study (first part of this study study) was carried out to investigate the solidification process in a copper continuous strip casting process. The model has been tuned by experimental results (i.e. cooling water flow measurements, temperature measurements and metallographic analysis). Further, the results have been used to study the possibility of improved productivity. In this report (second of the study) the flow pattern of the molten copper during a strip casting process as a manufacturing method has been studied using a full-scale water model. The dynamic similarity between model and real system has been studied. Six different types of inlet system to the mould have been studied: inlet nozzle jets with free stream, submerged nozzle jets, slot-submerged inlet system, semi slot-submerged inlet system, submerged-slot inlet nozzle jets and finally submerged-slot inlet nozzle jets with jet killer. Moreover, the effects of nozzle angle, nozzle diameter, casting speed, tundish adjustment and misalignment of the inlet nozzle jets on the flow pattern have been investigated. The vortex formation and bubble entrainment, depending upon the nozzle configuration, immersion depth and the fluid level in the mould have also been studied. It was found that the slot-submerged inlet nozzle jets with jet killer arrangement showed an obvious improvement of the fluid flow characteristics, yielding better tracer distribution in the flow pattern, lower values of back mixing flow, lower turbulence and lower vortex and recirculation flow.

Statistical properties of Hα jets in the polar coronal hole and their implications in coronal activities

Context. Dynamic features such as chromospheric jets, transition region network jets, coronal plumes, and coronal jets are abundant in the network regions of polar coronal holes on the Sun. Aims. We investigate the relationship between chromospheric jets and coronal activities, such as coronal plumes and jets. Methods. We analyzed observations of a polar coronal hole including the filtergrams taken by the New Vacuum Solar Telescope at the Hα − 0.6 Å to study the Hα jets, as well as the Atmospheric Imaging Assembly 171 Å images to follow the evolution of coronal activities. Results. The Hα jets are persistent in the network regions, with only some regions (denoted as R1–R5) rooted in discernible coronal plumes. With an automated method, we identified and tracked 1320 Hα jets in the network regions. We find that the average lifetime, height, and ascending speed of the Hα jets are 75.38 s, 2.67 Mm, 65.60 km s−1, respectively. The Hα jets rooted in R1–R5 are higher and faster than those in the others. We also find that propagating disturbances (PDs) in coronal plumes have a close connection with the Hα jets. The speeds of 28 out of 29 Hα jets associated with PDs are ≳50 km s−1. In the case of a coronal jet, we find that the speeds in both the coronal jet and the Hα jet are over 150 km s−1, suggesting that both cool and hot jets can be coupled. Conclusions. Based on our analyses, it is evident that more dynamic Hα jets could release their energy to the corona, which might be the result of a Kelvin-Helmholtz instability developing or that of small-scale magnetic activities. We suggest that chromospheric jets, transition region network jets, and ray-like features in the corona are coherent phenomena that serve as important vehicles for cycling energy and mass in the solar atmosphere.

Калориметрические исследования СВЧ ионного двигателя

The authors continue their work in the field of calorimetric studies of the parameters of an accelerated ionized gas jet of prototypes of microwave ion micro-thrusters with an energy consumption of up to 10 watts. This paper presents an improved calorimetric method. The introduction into the design of a heat receiver in the form of a thin screen makes it possible to allocate the thermal component formed by the passage of an electric current through the plasma in the accelerating gap. Calorimetric studies of the prototype with a two-electrode accelerating system are carried out at the same accelerating voltages and power of the microwave generator and different mass gas flow rates. It is shown that at a nitrogen consumption of 5,668•10–9 kg/s, the velocity of the mixed jet (neutral gas with ionized component) of the gas was 63,75 m/s, the jet thrust is 0,36 μN. With a nitrogen consumption of 1,611•10–8 kg/s, the speed of the mixed gas jet was 47,9 m/s, the jet thrust was 0,77 μN.

Study on Tunnel Air Curtain Insulation System for Cold Areas

With the growing number of tunnels in high‐latitude and high‐altitude areas, freezing damage is all the more obvious. In traditional insulation layer method, insulation layer is laid in the tunnel to prevent invasion of cold air by taking advantage of its low thermal conductivity. However, due to its narrow temperature adaptation range and high construction and maintenance costs, this method cannot completely solve the problem of tunnel freezing damage. To solve this problem, this paper proposes tunnel air curtain insulation system which can generate electricity using solar energy. Based on parameters such as indoor air temperature and wind velocity in the thermal insulation room, on the one hand, it intelligently controls running sets of air curtain, jet flow angle, and velocity, prevents invasion of the external cold temperature into the tunnel, so that the tunnel maintains an interior temperature above 0°C. On the other hand, it intelligently diagnoses air curtain machine to provide system fault warning, so that the system keeps safe and reliable operation. The results show that air curtain technology can effectively solve the problem of tunnel freezing damage in cold areas; multiple air curtains in series connection provide better barrier efficiency. From the measured data and calculation results of Lafashan tunnel, it can be seen that an air curtain is installed at the tunnel portal with jet speed of 22.7 m/s and temperature of 35.24°C, which can meet the tunnel without freezing damage when the external temperature is −10°C, and the external wind speed is 2 m/s, providing a new method for tunnel insulation technology in cold area.

Turbulence-driven magnetic reconnection and the magnetic correlation length: Observations from Magnetospheric Multiscale in Earth's magnetosheath

Turbulent plasmas generate a multitude of thin current structures that can be sites for magnetic reconnection. The Magnetospheric Multiscale (MMS) mission has recently enabled the detailed examination of such turbulent current structures in Earth's magnetosheath and revealed that a novel type of reconnection, known as electron-only reconnection, can occur. In electron-only reconnection, ions do not have enough space to couple to the newly reconnected magnetic fields, suppressing ion jet formation and resulting in thinner sub-proton-scale current structures with faster super-Alfvénic electron jets. In this study, MMS observations are used to examine how the magnetic correlation length (λC) of the turbulence, which characterizes the size of the large-scale magnetic structures and constrains the length of the current sheets formed, influences the nature of turbulence-driven reconnection. We systematically identify 256 reconnection events across 60 intervals of magnetosheath turbulence. Most events do not appear to have ion jets; however, 18 events are identified with ion jets that are at least partially coupled to the reconnected magnetic field. The current sheet thickness and electron jet speed have a weak anti-correlation, with faster electron jets at thinner current sheets. When λC≲20 ion inertial lengths, as is typical near the sub-solar magnetosheath, a tendency for thinner current sheets and potentially faster electron jets is present. The results are consistent with electron-only reconnection being more prevalent for turbulent plasmas with relatively short λC and may be relevant to the nonlinear dynamics and energy dissipation in turbulent plasmas.

Astrophysical Neutrinos and Blazars

We review and discuss recent results on the search for correlations between astrophysical neutrinos and γ-ray-detected sources, with many extragalactic studies reporting potential associations with different types of blazars. We investigate possible dependencies on blazar sub-classes by using the largest catalogues and all the multi-frequency data available. Through the study of similarities and differences in these sources we conclude that blazars come in two distinct flavours: LBLs and IHBLs (low-energy-peaked and intermediate-high-energy-peaked objects). These are distinguished by widely different properties such as the overall spectral energy distribution shape, jet speed, cosmological evolution, broad-band spectral variability, and optical polarisation properties. Although blazars of all types have been proposed as neutrino sources, evidence is accumulating in favour of IHBLs being the counterparts of astrophysical neutrinos. If this is indeed the case, we argue that the peculiar observational properties of IHBLs may be indirectly related to proton acceleration to very high energies.

MOJAVE. XIX. Brightness Temperatures and Intrinsic Properties of Blazar Jets

Abstract We present multiepoch, parsec-scale core brightness temperature observations of 447 active galactic nucleus (AGN) jets from the MOJAVE and 2 cm Survey programs at 15 GHz from 1994 to 2019. The brightness temperature of each jet over time is characterized by its median value and variability. We find that the range of median brightness temperatures for AGN jets in our sample is much larger than the variations within individual jets, consistent with Doppler boosting being the primary difference between the brightness temperatures of jets in their median state. We combine the observed median brightness temperatures with apparent jet speed measurements to find the typical intrinsic Gaussian brightness temperature of 4.1( ± 0.6) × 1010 K, suggesting that jet cores are at or below equipartition between particle and magnetic field energy in their median state. We use this value to derive estimates for the Doppler factor for every source in our sample. For the 309 jets with both apparent speed and brightness temperature data, we estimate their Lorentz factors and viewing angles to the line of sight. Within the BL Lac optical class, we find that high-synchrotron-peaked BL Lacs have smaller Doppler factors, lower Lorentz factors, and larger angles to the line of sight than intermediate and low-synchrotron-peaked BL Lacs. We confirm that AGN jets with larger Doppler factors measured in their parsec-scale radio cores are more likely to be detected in γ rays, and we find a strong correlation between γ-ray luminosity and Doppler factor for the detected sources.

An analytical model for prediction of denudation zone width in laser powder bed fusion additive manufacturing

Accurately modeling the physics of laser-powder interaction is needed for predicting the probabilities of performance-limiting defects in parts additively manufactured using laser powder bed fusion. In this paper, we present an analytical model for rapid prediction of denudation width in laser powder bed fusion additive manufacturing process. The model is based on the force balance analysis for a powder particle sitting on top of the powder bed. The model relates the laser power and laser scan speed to the vapor jet speed and consequently to the inward entrainment gas velocity. The effects of laser power and laser speed on denudation width are investigated and compared with experimental data. In addition, a criterion for the onset of denudation is presented which accounts for chamber gas, powder particle size and density. The results show that for a given laser power the denudation width increases as the laser speed decreases.

Coolant condition and spindle power in high-efficiency-deep-grinding of nickel-based superalloy profile part

ABSTRACT Coolants play an important role in controlling thermal damage in high-efficiency deep grinding (HEDG). The cooling condition in the grinding contact zone (GCZ) determines the cooling effect during the grinding process. Furthermore, when profile grinding is performed, owing to the complexity of the shape, the cooling effect varies at different positions. Therefore, in this study, a device that includes a pressure sensor and semi-natural thermocouples was introduced to evaluate the cooling conditions in the GCZ during HEDG. Thereafter, the influences of the grinding parameters and outlet velocity of the coolant on the pressure distribution were investigated. The grinding speed and outlet velocity of the coolant have significant impacts on the cooling condition, whereas the influences of the infeed speed and depth of cut are limited. The coolant pressure distributions during the profile grinding were measured, analyzed, and optimized. The needle-shaped nozzle, which adapts to the profile, has a better cooling effect than the shoe-shaped nozzle. Moreover, the influence of the coolant delivery on the spindle power was discussed. The outlet velocity of the coolant jet and grinding speed have significant effects on the idle and grinding powers. Therefore, it is recommended to consider the influence of grinding speed during HEDG.

The Multiweek Thermal Stability of Medical-Grade Poly(ε-caprolactone) During Melt Electrowriting.

Melt electrowriting (MEW) is a high-resolution additive manufacturing technology that places unique constraints on the processing of thermally degradable polymers. With a single nozzle, MEW operates at low throughput and in this study, medical-grade poly(ε-caprolactone) (PCL) is heated for 25 d at three different temperatures (75, 85, and 95°C), collecting daily samples. There is an initial increase in the fiber diameter and decrease in the jet speed over the first 5 d, then the MEW process remains stable for the 75 and 85°C groups. When the collector speed is fixed to a value at least 10% above the jet speed, the diameter remains constant for 25 d at 75°C and only increases with time for 85 and 95°C. Fiber fusion at increased layer height is observed for 85 and 95°C, while the surface morphology of single fibers remain similar for all temperatures. The properties of the prints are assessed with no observable changes in the degree of crystallinity or the Young's modulus, while the yield strength decreases in later phases only for 95°C. After the initial 5-d period, the MEW processing of PCL at 75°C is extraordinarily stable with overall fiber diameters averaging 13.5 ± 1.0 µmoverthe entire 25-d period.

Preparation of Polyimide Nanofiber Membranes and Interlaminar Toughness Investigation of Their Toughened Composites

Interlaminar delamination and brittle fracture of matrix have been a dilemma that fiber-reinforced composites have been faced with. Herein, the polyimide (PI) nanofiber-toughened glass fiber fiber-reinforced epoxy composites were prepared by electrospinning method and subsequent vacuum assistant resin transfer molding. The effect of spinning parameters including PI concentration, applied voltage, collector distance, jet speed and ambient humidity on the resultant fiber diameter and its distribution was systematically evaluated. The surface properties of obtained PI nanofibers were characterized by FT-IR, TG-DSC and water contact angle. The effect of PI concentration on tensile strength of PI membranes was also studied. The mode I (G[Formula: see text] and mode II (G[Formula: see text] interlaminar fracture toughness were measured. The results indicated that GIc and GIIc increased by 127.69% and 85.33%. The improvement of interlaminar fracture toughness may be attributed to the bridging effect of PI nanofibers.