Jet Direction Research Articles

Jet-induced enhancement of deuteron production in pp and p-Pb collisions at the LHC

Jet-associated deuteron production in pp collisions at s=13 TeV and p-Pb collisions at sNN=5.02 TeV is studied in the coalescence model by using the phase-space information of proton and neutron pairs from a multiphase transport (AMPT) model at the kinetic freezeout. In the low transverse momentum (pT) region pT/A<1.5 GeV/c, where A is the mass number of a nucleus, the in-jet coalescence factor B2In-jet for deuteron production, given by the ratio of the in-jet deuteron number to the square of the in-jet proton number, is found to be larger than the coalescence factor B2 in the medium perpendicular to the jet by a factor of about 10 in pp collisions and of 25 in p−Pb collisions, which are consistent with the ALICE measurements at the LHC. Such large low-momentum enhancements mainly come from coalescence of nucleons inside the jet with the medium nucleons. Coalescence of nucleons inside the jet dominates deuteron production only at the higher pT region of pT/A≳4 GeV/c, where both the yield ratio d/p of deuteron to proton numbers and the B2 are also significantly larger in the jet direction than in the direction perpendicular to the jet due to the strong collinear correlation among particles produced from jet fragmentation. Studying jet-associated deuteron production in relativistic nuclear collisions thus opens up a new window to probe the phase-space structure of nucleons inside jets.

Polarization of active galactic nuclei with significant VLBI-Gaia displacements

Context. Numerous studies have reported significant displacements in the coordinates of active galactic nuclei (AGNs) between measurements using the very-long-baseline-interferometry (VLBI) technique and those obtained by the Gaia space observatory. There is consensus that these discrepancies do indeed manifest astrometrically resolved sub-components of AGNs rather than random measurement noise. Among other evidence, it has been reported that AGNs with VLBI-to-Gaia displacements (VGDs) pointing downstream of their parsec-scale radio jets exhibit higher optical polarization compared to sources with the opposite (upstream) VGD orientation. Aims. We aim to verify the previously reported connection between optical polarization and a VGD-jet angle using a larger dataset of polarimetric measurements and updated Gaia DR3 positions. We also seek further evidence supporting the disk-jet dichotomy as an explanation of such a connection by using millimeter-wave polarization and multiband optical polarization measurements. Methods. We performed optical polarimetric observations of 152 AGNs using three telescopes. These data are complemented by other publicly available polarimetric measurements of AGNs. We cross-matched public astrometric data from VLBI and Gaia experiments, obtained corresponding positional displacements, and combined this catalog with the polarimetric and jet direction data. Results. Active galactic nuclei with downstream VGDs are confirmed to have significantly higher optical fractional polarization than the upstream sample. At the same time, the millimeter-wavelength polarization of the two samples shows very similar distributions. Conclusions. Our results support the hypothesis that the VGDs pointing down the radio jet are likely caused by a component in the jet emitting highly polarized synchrotron radiation and dominating in the overall optical emission. The upstream-oriented VGDs are likely to be produced by the low-polarization emission of the central engine’s subcomponents, which dominate in the optical.

Dynamics of single cavitation bubble collapse jet under particle-wall synergy

The interaction between a particle and a cavitation bubble significantly influences the erosive effect on the wall surface of flow passage components in fluid machinery. This paper investigates the dynamics of a single bubble collapse jet under the synergetic effects of a particle and a wall, using Kelvin impulse theory and high-speed photographic experiments. A theoretical model to predict the intensity and direction of the collapse jet at arbitrary locations near the particle and the wall is constructed on the basis of the image method and Weiss's theorem. The accuracy of the model is verified by comparison with a large number of experimental results. The mechanisms underlying the relative contributions of the particle and wall to the behavior of jet intensity and direction are explored. The effects of key parameters on jet intensity and direction are also quantitatively analyzed, including the relative positions of the particle, wall, and the bubble and the dimensionless particle radius. The main conclusions are as follows: (1) the particle will cause a deflection in the direction of the collapse jet near the wall, leading to the formation of a jet attraction zone. The proposed theoretical model effectively predicts the spatial location of this zone. (2) There exists a region in which the jet is weak, and there is a jet equilibrium point with zero impulse between the particle and the wall. The position of this equilibrium point gradually approaches the wall in a nonlinear manner with increasing particle size and in a quasi-linear manner with decreasing particle–wall distance. (3) When the particle and the bubble are the same distance from the wall, the jet direction gradually changes from toward the particle to vertical to the wall in a nonlinear manner as the bubble–particle distance increases. Moreover, the effective range of the particle's influence on the jet direction decreases as the particle–wall distance decreases.

Magnetic Field of the Quasar 1604+159 from Parsec to Kiloparsec Scale

Abstract We present a multifrequency polarimetric study for the quasar 1604+159. The source was observed at the L band with the American Very Long Baseline Array and the L, X, and U bands with the Very Large Array. These observations provide different resolutions from mas to arcsec, enabling us to probe the morphology and magnetic field from tens of parsec to hundreds of kiloparsec scale. We detect a symmetrical Fanaroff–Riley Class I–like structure. The source has several lobes and bulges, forming a cocoon shape. The polarization is normal to the edges of the structure with high fractional polarization up to ∼60%. Two hotspots are observed at the eastern and western sides of the source, located symmetrically relative to the core. The flux density ratio (&gt;1.5) between the two hotspots suggests the Doppler beaming effect exists at a large scale. The polarized emission in the hotspots also shows a symmetrical structure with an oblique direction from the jet direction. In general, the jet propagates in a collimating structure with several bends. Polarization is also detected perpendicular to the local jet from ∼100 mas to ∼1″. The jet shows strong polarized intensity and high fractional polarization at the bending edges. We discuss the possible origins of the observed structure and magnetic field.

Co-flow jets application for occupant targeted ventilation: Focus on thermal comfort and air quality

Co-flow air jets can be used in occupant-targeted ventilation, such as personalized ventilation, stratum ventilation, aiming at improving air quality in the breathing zone of occupants. However, these have not been studied sufficiently. The velocity field and cleanness of co-flow jets comprising inner jet of clean air encircled by outer jet of room air were studied under isothermal conditions by physical measurements and CFD simulations at numerous combinations of initial diameter and velocity of the inner and outer jets appropriate for practical application. The co-flow jet had a lower axial velocity decay along the jet direction than that of the single jet. The magnitude (turbulence intensity) and frequency of the velocity fluctuations in co-flow jets were lower compared to those in a single jet. The results revealed that with regard to thermal comfort co-flow jets may provide more cooling compared to single jets, especially when supplied toward to the user. The level of cleanness depended on the initial velocity of the inner and outer jets as well as their diameters. The air on the jet axis of the co-flow was up to 40 % cleaner compared to the single jet. The increased area ratio of outer nozzle to inner nozzle from 1.0 to 3.0 improved the cleanness of the air by at least 10 % to the distance from 8 to 14 initial diameters compared to a single jet. The co-flow jet with velocity ratio of 1.5 had longest concentration core length, Lu, (up to 6 initial diameters to the inner jet) with clean air. The results can be used for design of occupant targeted ventilation.

Clues of the restarting active galactic nucleus activity of Mrk 1498 from GTC/MEGARA integral field spectroscopy data

Some giant radio galaxies selected at X-rays with active galactic nuclei (AGN) show signs of a restarted nuclear activity (old lobes plus a nuclear young radio source probed by giga-hertz peaked spectra). The study of these sources gives us insights into the AGN activity history. More specifically, the kinematics and properties of the outflows can be used as a tool to describe the activity of the source. One object in this peculiar class is Mrk\,1498, a giant low-frequency double radio source that shows extended emission in O\,III . This emission is likely related to the history of the nuclear activity of the galaxy. We investigate whether this bubble-like emission might trace an outflow from either present or past AGN activity. Using a medium-resolution spectroscopy (R\,sim \,10\,000) available with MEGARA/GTC, we derived kinematics and fluxes of the ionised gas from modelling the O\,III and Hbeta features. We identified three kinematic components and mapped their kinematics and flux. All the components show an overall blue to red velocity pattern, with similar peak-to-peak velocities but a different velocity dispersion. At a galactocentric distance of sim \,2.3\,kpc, we found a blob with a velocity up to 100\ and a high velocity dispersion (sim \,170\ that is spatially coincident with the direction of the radio jet. The observed O\,III /Hbeta line ratio indicates possible ionisation from AGN or shocks nearly everywhere. The clumpy structure visibile in HST images at kiloparsec scales show the lowest values of log O\,III /Hbeta ($&lt;$\,1), which is likely not related to the photoionisation by the AGN. Taking optical and radio activity into account, we propose a scenario of two different ionised gas features over the radio AGN lifecycle of Mrk\,1498. The radio emission suggests at least two main radio activity episodes: an old episode at megaparsec scales (formed during a time span of sim \,100\,Myr), and a new episode from the core ($&gt;$\,2000\,yr ago). At optical wavelengths, we observe clumps and a blob that are likely associated with fossil outflow. The latter is likely powered by past episodes of the flickering AGN activity that may have occurred between the two main radio phases.

Fluid Dynamics of Interacting Rotor Wake with a Water Surface

Rotor-type cross-media vehicles always induce considerably complex mixed air–water flows when approaching the water surface, resulting in relative thrust loss and structural damage on rotor. The interactions between a water surface and rotor wake bring potential risks to the cross-media process, which is known as the near-water effect of the rotor. In this paper, experimental investigations are used to explore the fluid dynamics of the near-water effect of the rotor. Qualitative droplet observation was carried out on the 0.25 m and 0.56 m diameter commercial rotor blades and the 0.07 m diameter ducted fan near the water surface first to gain a qualitative understanding of droplet characteristics. The results show that the rotor wake caused water surface deformation, droplet tearing off, splashing, and entrainment into the rotor disk. The depression formed by the rotor downwash flow impacting the water surface is named as three modes: dimpling, splashing, and penetrating, and the correlation between the depression modes and the aerodynamic characteristics of the rotor is primary analyzed. The flow mechanisms of dimpling mode were studied using the particle image velocimetry (PIV) technique. The results showed that the cavity and liquid crown obviously alter the flow direction of water surface jets, but not all rotors near water enter the vortex ring state. Two splashing mechanisms were revealed, including the direct ejection of droplets at the rim of depression and the tearing of liquid crown by the water surface jets. The blade tip vortex in the surface jet is a potential cause of entrainment into the rotor disk and secondary breakup of the droplet.

Impact of the grade and jet-flow direction of residual aortic regurgitation after valve-sparing root replacement

ObjectivesTo investigate the impact of the grade and jet direction of residual aortic regurgitation (rAR) after valve-sparing root replacement (VSRR). MethodsThe study enrolled 248 adult patients who underwent VSRR between 1995 and 2021. The patients were divided into groups based on the postoperative rAR. Patients with rAR were further categorized according to rAR grade and jet direction. The primary endpoint was the development of aortic regurgitation of moderate or greater (≥moderate) severity and/or the need for valve replacement during the follow-up, analyzed by a multivariable competing risk analysis. The secondary endpoints included the occurrence of rAR and overall survival. ResultsThe median age of the patients was 36.5 years, and 79.8% had been diagnosed with connective tissue disease. After VSRR, 146 patients did not present with rAR; however, 102 had rAR (77 with minimal central, 18 with minimal eccentric, and 7 with mild rAR). The 5-year and 8-year incidence rates of the primary endpoint were 14.6% and 17.9%, respectively. rAR was a significant risk factor (P = .001), and eccentricity and mild rAR seemed to have important roles. The risk factors for rAR included dilated root, preoperative moderate regurgitation, and redo sternotomy. Overall survival was influenced only by age. ConclusionsrAR after VSRR operation could be a risk factor for AR progression. Minimal central rAR generally has a tolerable clinical course; however, patients with even minimal eccentric AR may develop AR progression, so active surveillance and timely management might be required. Furthermore, early VSRR can help reduce the rAR.

Dynamics of femtosecond laser-driven liquid jets

The complex dynamics of flowing liquids under external stimuli can lead to significant changes in the direction of liquid jets. In this study, we utilized a femtosecond laser to drive a flowing liquid column and analyzed the effect of varying laser energies on the direction of the liquid flow. Additionally, we examined how the diameter and volume of the liquid column influenced its directional behavior when driven by the laser. By comparing the driving angles under different conditions, we explored the principles governing the femtosecond laser-driven liquid columns. These findings offer valuable insights into the field of liquid dynamics, showcasing femtosecond lasers as a good method for controlling liquid flows.

Experimental study of rotating direction for dual-axial swirlers on the flow field and combustion characteristics of aero-engine combustor

The flow field structure for aero-engine combustor is one of the most important factors for combustion performance. To investigate how the rotating direction of dual-axial swirlers affects the flow field and combustion characteristics, particle image velocimetry (PIV) experiments were conducted in the primary combustion and intermediate zones. Additionally, planar laser induced fluorescence (PLIF) was used to map the distribution of kerosene and OH in the primary combustion zone. The results show that the swirling jets in co-swirl exhibit greater jet momentum, resulting in a longer primary recirculation zone and a larger deflection angle of the primary jets. This ultimately leads to a higher recirculation rate compared to counter-swirl. The primary jets define the boundary of the flow field structure. The rotating direction primarily affects the flow field structure upstream of the primary jets, exerts a relatively weaker influence on the intermediate zone, which is mainly affected by the deflection direction of the primary jets, and essentially has no impact on the dilution jets. Co-swirl has a relatively stable flow field than counter-swirl, whereas the flow field in counter-swirl is more chaotic, featuring a greater number of vortex cores in the primary recirculation zone. The coupling between the primary and swirling jets affects the mass transfer direction in the intermediate zone, which is reflected in the fact that the mass transfer is from top-left to bottom-right in co-swirl, while it is in the opposite direction in counter-swirl. OH is predominantly found in the swirling shear layers, the primary and secondary combustion zones, whereas kerosene is mainly concentrated in the shear layers of swirling jets. The kerosene distribution in co-swirl shows a larger and more concentrated expansion angle compared to counter-swirl. In contrast, the OH distribution downstream of counter-swirl is broader, with more intense combustion due to enhanced kerosene decomposition and fuel-air mixing. The smaller primary recirculation zone in counter-swirl forces the primary combustion zone to extend downstream, leading to a more intense reaction in the secondary recirculation zone.

Two Models for the Orbital Modulation of Gamma Rays in Cyg X-3

We model the currently available γ-ray data on Cyg X-3 from the Fermi Large Area Telescope. Thanks to Cyg X-3’s very strong γ-ray activity during 2018–2021, the data quality has significantly improved. We study the strong orbital modulation of the γ-rays observed at high γ-ray fluxes. The modulation, as found earlier, is well modeled by anisotropic Compton scattering of the donor blackbody emission by relativistic electrons in a jet strongly misaligned with respect to the orbital axis. We confirm that this model fits well both the average γ-ray modulation light curve and the spectrum. However, we find that if the jet were aligned with the spin axis of a rotating black hole, it would undergo geodetic precession with a period of ∼50 yr. However, its presence is ruled out by both the γ-ray and radio data. Therefore, we consider an alternative model in which the average jet direction is aligned, but it is bent outside the orbit owing to the thrust of the donor stellar wind, and thus precesses at the orbital period. The γ-ray modulation then appears as a result of the variable Doppler boosting of synchrotron self-Compton jet emission. This model also fits the data well. However, the fitted bending angle is much larger than the theoretical one based on the binary and wind parameters as currently known. Thus, both models disagree with important aspects of our current theoretical understanding of the system. We discuss possible ways to find the correct model.

Numerical simulation of high-pressure jet fire in on-board hydrogen storage cylinders under fire conditions

Hydrogen fuel cell vehicles (HFCVs) may cause fires in the event of an accident. When the high-pressure hydrogen storage cylinders are exposed to fire for a long time, there will be a risk of catastrophic consequences such as leakage, jet fire and explosion. Fire test is the main method to study the safety performance of hydrogen storage cylinders. During the firing process, the wall and internal temperature of the hydrogen storage cylinder rise gradually, and the thermally activated pressure relief device (TPRD) of the cylinder reaches a certain temperature and then releases high-pressure hydrogen to prevent the cylinder from bursting. As the hydrogen storage cylinder is in the fire environment, the release of high-pressure hydrogen will be ignited to form a jet fire and cause damage to personnel and equipment. In this paper, CFD software Fluent was used to numerically simulate the local fire test of the hydrogen storage cylinder with high-temperature air as the fire source. The variation law of cylinder wall temperature, gas temperature and pressure inside the cylinder, and the activation of TPRD were analyzed. At the same time, on the basis of the fire test simulation, a high-pressure hydrogen jet fire simulation numerical model caused by the TPRD action was established. The velocity field, temperature field and hydrogen concentration distribution of the jet fire were obtained, and the overpressure generated by the jet fire and the flame length size were analyzed. The results show that the high-pressure hydrogen released by TPRD was ignited under the fire condition to produce a jet flame and generated an overpressure in the jet direction, and the influence range of the overpressure was smaller than the influence range of the jet flame.

Image-Based Computational Fluid Dynamics to Compare Two Repair Techniques for Mitral Valve Prolapse.

OBJECTIVE: The treatment of mitral valve prolapse involves two distinct repair techniques: chordal replacement (Neochordae technique) and leaflet resection (Resection technique). However, there is still a debate in the literature about which is the optimal one. In this context, we performed an image-based computational fluid dynamic study to evaluate blood dynamics in the two surgical techniques. METHODS: We considered a healthy subject (H) and two patients (N and R) who underwent surgery for prolapse of the posterior leaflet and were operated with the Neochordae and Resection technique, respectively. Computational Fluid Dynamics (CFD) was employed with prescribed motion of the entire left heart coming from cine-MRI images, with a Large Eddy Simulation model to describe the transition to turbulence and a resistive method for managing valve dynamics. We created three different virtual scenarios where the operated mitral valves were inserted in the same left heart geometry of the healthy subject to study the differences attributed only to the two techniques. RESULTS: We compared the three scenarios by quantitatively analyzing ventricular velocity patterns and pressures, transition to turbulence, and the ventricle ability to prevent thrombi formation. From these results, we found that the operative techniques affected the ventricular blood dynamics in different ways, with variations attributed to the reduced mobility of the Resection posterior leaflet. Specifically, the Resection technique resulted in turbulent forces, related with the risk of hemolysis formation, up to 640 Pa, while the other two scenarios exhibited a maximum of 240 Pa. Moreover, in correspondence of the ventricular apex, the Resection technique reduced the areas with low velocity to 15%, whereas the healthy case and the Neochordae case maintained these areas at 30 and 48%, respectively. Our findings suggest that the Neochordae technique developed a more physiological flow with respect to the Resection technique. CONCLUSION: Resection technique gives rise to a different direction of the mitral jet during diastole increasing the ability to washout the ventricular apex preventing from thrombi formation, but at the same time it promotes turbulence formation that is associated with ventricular effort and risk of hemolysis.

Radio Astrometry at Different Frequencies

The very long baseline interferometry technique allows us to determine the positions of thousands of radio sources using the absolute astrometry approach. I have investigated the impacts of a selection of observing frequencies in a range from 2 to 43 GHz in single-band, dual-band, and quad-band observing modes on astrometric results. I processed seven data sets in a range of 72,000 to 6.9 million observations, estimated source positions, and compared them. I found that source positions derived from dual-band, quad-band, and 23.6 GHz single-band data agree at a level below 0.2 mas. Comparison of independent data sets allowed me to assess the error levels of individual catalogs: 0.05–0.07 mas per position component. Further comparison showed that individual catalogs have systematic errors at the same level. The positions from 23.6 GHz single-band data show systematic errors related to the residual ionosphere contribution. Analysis of source position differences revealed systematic errors along jet directions at a level of 0.09 mas. Network-related systematic errors affect all the data, regardless of frequency. Comparison of position estimates allowed me to derive the stochastic error model that closes the error budget. Based on the collected evidence, I have made a conclusion that the development of frequency-dependent reference frames of the entire sky is not warranted. In most cases dual-band, quad-band, and single-band data at a frequency of 22 GHz and higher can be used interchangeably, which allows us to exploit the strength of a specific frequency setup for given objects. Mixing observations at different frequencies causes errors not exceeding 0.07 mas.

Toward occupant-centric system: Multicriteria optimization of hybrid displacement–personalized ventilation system using computational fluid dynamics with computer-simulated person

Engineers have integrated general ventilation systems with personalized ventilation (PV) to achieve energy efficiency while providing good indoor air quality (IAQ) and thermal comfort. Previous studies conducted parametric analyses of PV by varying its flow rate and temperature, analyzing energy, IAQ, and thermal comfort while keeping main ventilation settings constant, even though the latter significantly affect the general flow field. Therefore, computational fluid dynamics simulation is performed to simultaneously optimize the above-mentioned three outputs in an office with displacement ventilation (DV) and PV by varying the DV supply flow rate and temperature, the fraction of outlet air being resupplied to inlet or DV recirculation, and PV supply flow rate and temperature. We utilize the Taguchi design to minimize the number of simulations as well as use the “technique for order preference by similarity to ideal solution” (TOPSIS) coupled with Taguchi's signal-to-noise ratio analysis for optimization. Four optimization cases are investigated by varying the thermal comfort and IAQ parameters from volume-averaged to occupant-centric values, such as the skin temperature and inhaled concentration. Results show that occupant-centric optimization presents low energy requirements with acceptable IAQ and thermal comfort compared with volume-averaged optimization, which can be attributed to imperfect mixing conditions. Furthermore, the DV settings and thermal plumes significantly affect the direction of jet released by the PV, which does not improve the IAQ. This underscores the importance of considering the aforementioned effects in maximizing the PV potential. Nevertheless, the PV system functions as intended under a flow rate of 6 L/s.

The NNLO soft function for N-jettiness in hadronic collisions

We compute the N-jettiness soft function in hadronic collisions to next-to-next-to-leading order (NNLO) in the strong-coupling expansion. Our calculation is based on an extension of the SoftSERVE framework to soft functions that involve an arbitrary number of lightlike Wilson lines. We present numerical results for 1-jettiness and 2-jettiness, and illustrate that our formalism carries over to a generic number of jets by calculating a few benchmark points for 3-jettiness. We also perform a detailed analytic study of the asymptotic behaviour of the soft-function coefficients at the edges of phase space, where one of the jets becomes collinear to another jet or beam direction, and comment on previous calculations of the N-jettiness soft function.

Simulations of pulsed overpressure jets: formation of bellows and ripples in galactic environments

ABSTRACT Jets from active nuclei may supply the heating which moderates cooling and accretion from the circum-galactic medium. While steady overpressured jets can drive a circulatory flow, lateral energy transfer rarely exceeds 3 per cent of jet power, after the initial bow shock has advanced. Here, we explore if pulses in high-pressure jets are capable of sufficient lateral energy transfer into the surrounding environment. We answer this by performing a systematic survey of numerical simulations in an axisymmetric hydrodynamic mode. Velocity pulses along low Mach jets are studied at various overpressures. We consider combinations of jet velocity pulse amplitude and frequency. We find three flow types corresponding to slow, intermediate, and fast pulsations. Rapid pulsations in light jets generate a series of travelling shocks in the jet. They also create ripples which propagate into the ambient medium while a slow convection flow brings in ambient gas which is expelled along the jet direction. Long period pulses produce slowly evolving patterns which have little external effect, while screeching persists as in non-pulsed jets. In addition, rapid pulses in jets denser than the ambient medium generate a novel breathing cavity analogous to a lung. Intermediate period pulses generate a series of bows via a bellows action which transfer energy into the ambient gas, reaching power efficiencies of over 30 per cent when the jet overpressure is sufficiently large. This may adequately inhibit galaxy gas accretion. In addition, such pulses enhance the axial out-flow of jet material, potentially polluting the circum-galactic gas with metal-enriched interstellar gas.

Surface characteristics evolution under the controllable impact cycles of an interrupted discrete waterjet

The interrupted discrete waterjet (DWJ) offers advantages in surface treatment due to its exceptional load characteristics and high controllability. However, the surface characteristics of materials under controllable DWJ parameters have not been fully elucidated. This study delves into the surface morphology, roughness parameters, microhardness, residual stress, and distribution of crystal characteristics in both the depth and radial directions under 2400–36,000 impact cycles of DWJ through peening experiments and material characterization. The findings indicate that the surface morphology is influenced by high-frequency roughness components with limited impact cycles, while low-frequency waviness components gradually take precedence with more impact cycles. As impact cycles increase, certain roughness parameters such as Sq, S5p, S5v, and S10z initially rise until 21,600 cycles, after which they fluctuate within a specific range. Furthermore, DWJ peening leads to an increase in maximum hardness with impact cycles, with the depth of peak value transitioning from the surface layer to the subsurface. The residual compressive stress initially increases and then decreases with impact cycles. Under the experimental conditions, the maximum hardness reaches 268.1HV0.3, a 49.95 % increase from the original state, and the peak residual compressive stress reaches 297.7 MPa with a 310.2 % increase. As impact cycles continue to rise, a balance between material removal and surface hardening is achieved, resulting in the stabilization of maximum hardness and compressive stress as erosion strength grows. Following DWJ peening, there is an increase in the percentage of low-angle grain boundaries, along with enhanced grain refinement, increased geometrically necessary dislocation (GND) density, and the emergence of new phases. As the impact cycles increase, the effects of DWJ peening on crystal grains become more pronounced. Additionally, it has been observed that the lateral jetting influence extends further horizontally than in the depth direction of the incoming jet. It is considered that cyclic hardening and high strain rate effects (1.2 × 104) play significant roles in material hardening and failure.

Assessment of echocardiographic interpretation of dual-lumen cannula during venovenous extracorporeal membrane oxygenation use for pediatric respiratory failure.

Echocardiography is considered essential during cannulation placement and manipulations. Literature evaluating transthoracic echocardiography (TTE) usage during pediatric VV-ECMO is scant. The purpose of this study is to describe the use of echocardiography during VV-ECMO at a large, quaternary children's hospital. A retrospective, single-year cohort study was performed of pediatric patients on VV-ECMO via dual-lumen cannula at our institution from January 2019 through December 2019. For each echocardiogram, final cannula component (re-infusion port (ReP), distal tip, proximal port and distal port) positions were evaluated by one echocardiographer. For TTEs with ReP in the right atrium, two echocardiographers independently evaluated ReP direction using 2-point (Yes/No) and 4-point scales, which were semi-quantitative protocols using color Doppler images to estimate ReP jet direction to the tricuspid valve. Cohen's kappa or weighted kappa was used to measure interrater agreement. During study period, 11 patients (64% male) received VV-ECMO with 49 TTEs and one transesophageal echocardiogram performed. The median patient age was 4.3 years [IQR: 1.1-11.5] and median VV-ECMO run time of 192h [90-349]. The median time between TTEs on VV-ECMO was 34h [8.3-65]. Most common position for the ReP was the right atrium (n=33, 67%), and ReP location was not identified in five TTEs (10%). For ReP flow direction, echocardiographers agreed on 82% of TTEs using 2-point evaluation. There was only moderate agreement between echocardiographers on the 2-point and 4-point assessments (k=.54, kw=.46 respectively). TTE is the predominant cardiac ultrasound modality used during VV-ECMO for pediatric respiratory failure. Subjective evaluation of VV-ECMO ReP jet direction in the right atrium is challenging, regardless of assessment method.

IXPE observation of PKS 2155-304 reveals the most highly polarized blazar

We report the X-ray polarization properties of the high-synchrotron-peaked (HSP) blazar PKS 2155$-$304 based on observations with the Imaging X-ray Polarimetry Explorer (IXPE). We observed the source between Oct 27 and Nov 7, 2023. We also conducted an extensive contemporaneous multiwavelength (MW) campaign. We find that during the first half ($T_1$) of the IXPE pointing, the source exhibited the highest X-ray polarization degree detected for an HSP blazar thus far, (30.7pm 2.0)&lt;!PCT!&gt;; this dropped to (15.3pm 2.1)&lt;!PCT!&gt; during the second half ($T_2$). The X-ray polarization angle remained stable during the IXPE pointing at 129.4 and 125.4 during $T_1$ and $T_2$, respectively. Meanwhile, the optical polarization degree remained stable during the IXPE pointing, with average host-galaxy-corrected values of (4.3pm 0.7)&lt;!PCT!&gt; and (3.8pm 0.9)&lt;!PCT!&gt; during the $T_1$ and $T_2$, respectively. During the IXPE pointing, the optical polarization angle changed achromatically from sim 140 to sim 90 and back to sim 130 Despite several attempts, we only detected (99.7&lt;!PCT!&gt; conf.) the radio polarization once (during $T_2$, at 225.5 GHz): with degree (1.7pm 0.4)&lt;!PCT!&gt; and angle 112.5 The direction of the broad pc-scale jet is rather ambiguous and has been found to point to the east and south at different epochs; however, on larger scales (&gt; 1.5 pc) the jet points toward the southeast (sim 135 similarly to all of the MW polarization angles. Moreover, the X-ray-to-optical polarization degree ratios of sim 7 and sim 4 during $T_1$ and $T_2$, respectively, are similar to previous IXPE results for several HSP blazars. These findings, combined with the lack of correlation of temporal variability between the MW polarization properties, agree with an energy-stratified shock-acceleration scenario in HSP blazars.