Recurrent flow patterns as a basis for two-dimensional turbulence: Predicting statistics from structures.

A dynamical systems approach to turbulence envisions the flow as a trajectory through a high-dimensional state space [Hopf, Commun. Appl. Maths 1, 303 (1948)]. The chaotic dynamics are shaped by the unstable simple invariant solutions populating the inertial manifold. The hope has been to turn this picture into a predictive framework where the statistics of the flow follow from a weighted sum of the statistics of each simple invariant solution. Two outstanding obstacles have prevented this goal from being achieved: 1) paucity of known solutions and 2) the lack of a rational theory for predicting the required weights. Here, we describe a method to substantially solve these problems, and thereby provide compelling evidence that the probability density functions (PDFs) of a fully developed turbulent flow can be reconstructed with a set of unstable periodic orbits. Our method for finding solutions uses automatic differentiation, with high-quality guesses constructed by minimizing a trajectory-dependent loss function. We use this approach to find hundreds of solutions in turbulent, two-dimensional Kolmogorov flow. Robust statistical predictions are then computed by learning weights after converting a turbulent trajectory into a Markov chain for which the states are individual solutions, and the nearest solution to a given snapshot is determined using a deep convolutional autoencoder. In this study, the PDFs of a spatiotemporally chaotic system have been successfully reproduced with a set of simple invariant states, and we provide a fascinating connection between self-sustaining dynamical processes and the more well-known statistical properties of turbulence.

Wall shear stress and pressure patterns in aortic stenosis patients with and without aortic dilation captured by high-performance image-based computational fluid dynamics.

Spatial patterns of elevated wall shear stress and pressure due to blood flow past aortic stenosis (AS) are studied using GPU-accelerated patient-specific computational fluid dynamics. Three cases of moderate to severe AS, one with a dilated ascending aorta and two within the normal range (root diameter less than 4cm) are simulated for physiological waveforms obtained from echocardiography. The computational framework is built based on sharp-interface Immersed Boundary Method, where aortic geometries segmented from CT angiograms are integrated into a high-order incompressible Navier-Stokes solver. The key question addressed here is, given the presence of turbulence due to AS which increases wall shear stress (WSS) levels, why some AS patients undergo much less aortic dilation. Recent case studies of AS have linked the existence of an elevated WSS hotspot (due to impingement of AS on the aortic wall) to the dilation process. Herein we further investigate the WSS distribution for cases with and without dilation to understand the possible hemodynamics which may impact the dilation process. We show that the spatial distribution of elevated WSS is significantly more focused for the case with dilation than those without dilation. We further show that this focal area accommodates a persistent pocket of high pressure, which may have contributed to the dilation process through an increased wall-normal forcing. The cases without dilation, on the contrary, showed a rather oscillatory pressure behaviour, with no persistent pressure "buildup" effect. We further argue that a more proximal branching of the aortic arch could explain the lack of a focal area of elevated WSS and pressure, because it interferes with the impingement process due to fluid suction effects. These phenomena are further illustrated using an idealized aortic geometry. We finally show that a restored inflow eliminates the focal area of elevated WSS and pressure zone from the ascending aorta.

Attaining freshwater and estuarine-water soil saturation in an ecosystem-scale coastal flooding experiment.

Coastal upland forests are facing widespread mortality as sea-level rise accelerates and precipitation and storm regimes change. The loss of coastal forests has significant implications for the coastal carbon cycle; yet, predicting mortality likelihood is difficult due to our limited understanding of disturbance impacts on coastal forests. The manipulative, ecosystem-scale Terrestrial Ecosystem Manipulation to Probe the Effects of Storm Treatments (TEMPEST) experiment addresses the potential for freshwater and estuarine-water disturbance events to alter tree function, species composition, and ecosystem processes in a deciduous coastal forest in MD, USA. The experiment uses a large-unit (2000 m2), un-replicated experimental design, with three 50 m × 40 m plots serving as control, freshwater, and estuarine-water treatments. Transient saturation (5 h) of the entire soil rooting zone (0-30 cm) across a 2000 m2 coastal forest was attained by delivering 300 m3 of water through a spatially distributed irrigation network at a rate just above the soil infiltration rate. Our water delivery approach also elevated the water table (typically ~ 2 m belowground) and achieved extensive, low-level inundation (~ 8 cm standing water). A TEMPEST simulation approximated a 15-cm rainfall event and based on historic records, was of comparable intensity to a 10-year storm for the area. This characterization was supported by showing that Hurricane Ida's (~ 5 cm rainfall) hydrologic impacts were shorter (40% lower duration) and less expansive (80% less coverage) than those generated through experimental manipulation. Future work will apply TEMPEST treatments to evaluate coastal forest resilience to changing hydrologic disturbance regimes and identify conditions that initiate ecosystem state transitions.

Heat transport in Rayleigh-Bénard convection with linear marginality.

Recent direct numerical simulations (DNS) and computations of exact steady solutions suggest that the heat transport in Rayleigh-Bénard convection (RBC) exhibits the classical [Formula: see text] scaling as the Rayleigh number [Formula: see text] with Prandtl number unity, consistent with Malkus-Howard's marginally stable boundary layer theory. Here, we construct conditional upper and lower bounds for heat transport in two-dimensional RBC subject to a physically motivated marginal linear-stability constraint. The upper estimate is derived using the Constantin-Doering-Hopf (CDH) variational framework for RBC with stress-free boundary conditions, while the lower estimate is developed for both stress-free and no-slip boundary conditions. The resulting optimization problems are solved numerically using a time-stepping algorithm. Our results indicate that the upper heat-flux estimate follows the same [Formula: see text] scaling as the rigorous CDH upper bound for the two-dimensional stress-free case, indicating that the linear-stability constraint fails to modify the boundary-layer thickness of the mean temperature profile. By contrast, the lower estimate successfully captures the [Formula: see text] scaling for both the stress-free and no-slip cases. These estimates are tested using marginally-stable equilibrium solutions obtained under the quasi-linear approximation, steady roll solutions and DNS data. This article is part of the theme issue 'Mathematical problems in physical fluid dynamics (part 1)'.

Exact Traveling Wave Solutions in Viscoelastic Channel Flow.

Elasto-inertial turbulence (EIT) is a new, two-dimensional chaotic flow state observed in polymer solutions with possible connections to inertialess elastic turbulence and drag-reduced Newtonian turbulence. In this Letter, we argue that the origins of EIT are fundamentally different from Newtonian turbulence by finding a dynamical connection between EIT and an elasto-inertial linear instability recently found at high Weissenberg numbers [Garg et al., Phys. Rev. Lett. 121, 024502 (2018)PRLTAO0031-900710.1103/PhysRevLett.121.024502]. This link is established by isolating the first known exact coherent structures in viscoelastic parallel flows-nonlinear elasto-inertial traveling waves (TWs)-borne at the linear instability and tracking them down to substantially lower Weissenberg numbers where EIT exists. These TWs have a distinctive "arrowhead" structure in the polymer stretch field and can be clearly recognized albeit transiently in EIT as well as being attractors for EIT dynamics if the Weissenberg number is sufficiently large. Our findings suggest that the dynamical systems picture in which Newtonian turbulence is built around the coexistence of many (unstable) simple invariant solutions populating phase space carries over to EIT, though these solutions rely on elasticity to exist.

A vast, thin plane of corotating dwarf galaxies orbiting the Andromeda galaxy.

Dwarf satellite galaxies are thought to be the remnants of the population of primordial structures that coalesced to form giant galaxies like the Milky Way. It has previously been suspected that dwarf galaxies may not be isotropically distributed around our Galaxy, because several are correlated with streams of H I emission, and may form coplanar groups. These suspicions are supported by recent analyses. It has been claimed that the apparently planar distribution of satellites is not predicted within standard cosmology, and cannot simply represent a memory of past coherent accretion. However, other studies dispute this conclusion. Here we report the existence of a planar subgroup of satellites in the Andromeda galaxy (M 31), comprising about half of the population. The structure is at least 400 kiloparsecs in diameter, but also extremely thin, with a perpendicular scatter of less than 14.1 kiloparsecs. Radial velocity measurements reveal that the satellites in this structure have the same sense of rotation about their host. This shows conclusively that substantial numbers of dwarf satellite galaxies share the same dynamical orbital properties and direction of angular momentum. Intriguingly, the plane we identify is approximately aligned with the pole of the Milky Way's disk and with the vector between the Milky Way and Andromeda.

An age difference of two billion years between a metal-rich and a metal-poor globular cluster.

Globular clusters trace the formation history of the spheroidal components of our Galaxy and other galaxies, which represent the bulk of star formation over the history of the Universe. The clusters exhibit a range of metallicities (abundances of elements heavier than helium), with metal-poor clusters dominating the stellar halo of the Galaxy, and higher-metallicity clusters found within the inner Galaxy, associated with the stellar bulge, or the thick disk. Age differences between these clusters can indicate the sequence in which the components of the Galaxy formed, and in particular which clusters were formed outside the Galaxy and were later engulfed along with their original host galaxies, and which were formed within it. Here we report an absolute age of 9.9 ± 0.7 billion years (at 95 per cent confidence) for the metal-rich globular cluster 47 Tucanae, determined by modelling the properties of the cluster's white-dwarf cooling sequence. This is about two billion years younger than has been inferred for the metal-poor cluster NGC 6397 from the same models, and provides quantitative evidence that metal-rich clusters like 47 Tucanae formed later than metal-poor halo clusters like NGC 6397.

Risk factors associated with invasive orthopaedic interventions in males with haemophilia enrolled in the Universal Data Collection program from 2000 to 2010.

BACKGROUND: Invasive orthopaedic interventions (IOI) are often used to control recurrent haemarthrosis, pain and loss of joint function, in males with haemophilia (Factor VIII and Factor IX deficiency). AIM: Identify risk factors associated with IOIs in males with haemophilia enrolled in the Universal Data Collection (UDC) surveillance program from 2000 until 2010. METHODS: Data were collected on IOIs performed on patients receiving care in 130 haemophilia treatment centers in the United States annually by health care providers using standardized forms. IOIs included in this study are as follows: 1) synovectomy and 2) arthrodesis or arthroplasty (A/A). Information about potential risk factors was obtained from the preceding UDC visit if available, or from the same visit if not. Patients with no reported IOI at any of their UDC visits were the reference group for the analysis. Multivariate analyses were conducted to identify independent risk factors for synovectomies and arthrodesis/arthroplasty. RESULTS: Risk factors significantly associated with the two IOI categories were age, student status, haemophilia severity, number of joint bleeds within the last 6 months, HIV or hepatitis C (HCV) status. Multivariate analyses showed patients on continuous prophylaxis were 50% less likely to have had a synovectomy and were 40% less likely to have an A/A. CONCLUSIONS: This study shows modifiable risk factors, including management of bleeding episodes with a continuous prophylactic treatment schedule are associated with a decreased likelihood of IOIs in males with haemophilia.

A tidally distorted dwarf galaxy near NGC 4449.

NGC 4449 is a nearby Magellanic irregular starburst galaxy with a B-band absolute magnitude of -18 and a prominent, massive, intermediate-age nucleus at a distance from Earth of 3.8 megaparsecs (ref. 3). It is wreathed in an extraordinary neutral hydrogen (H I) complex, which includes rings, shells and a counter-rotating core, spanning ∼90 kiloparsecs (kpc; refs 1, 4). NGC 4449 is relatively isolated, although an interaction with its nearest known companion--the galaxy DDO 125, some 40 kpc to the south--has been proposed as being responsible for the complexity of its H I structure. Here we report the presence of a dwarf galaxy companion to NGC 4449, namely NGC 4449B. This companion has a V-band absolute magnitude of -13.4 and a half-light radius of 2.7 kpc, with a full extent of around 8 kpc. It is in a transient stage of tidal disruption, similar to that of the Sagittarius dwarf near the Milky Way. NGC 4449B exhibits a striking S-shaped morphology that has been predicted for disrupting galaxies but has hitherto been seen only in a dissolving globular cluster. We also detect an additional arc or disk ripple embedded in a two-component stellar halo, including a component extending twice as far as previously known, to about 20 kpc from the galaxy's centre.

Declining trends in invasive orthopedic interventions for people with hemophilia enrolled in the Universal Data Collection program (2000-2010).

INTRODUCTION: Recurrent joint hemarthroses due to hemophilia (Factor VIII and Factor IX deficiency) often lead to invasive orthopedic interventions to decrease frequency of bleeding and/or to alleviate pain associated with end-stage hemophilic arthropathy. AIM: Identify trends in invasive orthopedic interventions among people with hemophilia who were enrolled in the Universal Data Collection (UDC) program during the period 2000-2010. METHODS: Data were collected from 130 hemophilia treatment centers in the United States annually during the period 2000-2010, in collaboration with the Centers for Disease Control and Prevention (CDC). The number of visits in which an invasive orthopedic intervention was reported was expressed as a proportion of the total visits in each year of the program. Invasive orthopedic interventions consisted of arthroplasty, arthrodesis, and synovectomy. Joints included in this study were the shoulder, elbow, hip, knee, and ankle. RESULTS: A 5.6% decrease in all invasive orthopedic interventions in all joints of people with hemophilia enrolled in the UDC program over the 11-year study period was observed. CONCLUSIONS: These data reflect a declining trend in invasive orthopedic interventions in people with hemophilia. Further research is needed to understand the characteristics that may influence invasive orthopedic interventions.

Effect of a myosin regulatory light chain mutation K104E on actin-myosin interactions.

Familial hypertrophic cardiomyopathy (FHC) is the most common cause of sudden cardiac death in young individuals. Molecular mechanisms underlying this disorder are largely unknown; this study aims at revealing how disruptions in actin-myosin interactions can play a role in this disorder. Cross-bridge (XB) kinetics and the degree of order were examined in contracting myofibrils from the ex vivo left ventricles of transgenic (Tg) mice expressing FHC regulatory light chain (RLC) mutation K104E. Because the degree of order and the kinetics are best studied when an individual XB makes a significant contribution to the overall signal, the number of observed XBs in an ex vivo ventricle was minimized to ∼20. Autofluorescence and photobleaching were minimized by labeling the myosin lever arm with a relatively long-lived red-emitting dye containing a chromophore system encapsulated in a cyclic macromolecule. Mutated XBs were significantly better ordered during steady-state contraction and during rigor, but the mutation had no effect on the degree of order in relaxed myofibrils. The K104E mutation increased the rate of XB binding to thin filaments and the rate of execution of the power stroke. The stopped-flow experiments revealed a significantly faster observed dissociation rate in Tg-K104E vs. Tg-wild-type (WT) myosin and a smaller second-order ATP-binding rate for the K104E compared with WT myosin. Collectively, our data indicate that the mutation-induced changes in the interaction of myosin with actin during the contraction-relaxation cycle may contribute to altered contractility and the development of FHC.

The cluster Terzan 5 as a remnant of a primordial building block of the Galactic bulge.

Globular star clusters are compact and massive stellar systems old enough to have witnessed the entire history of our Galaxy, the Milky Way. Although recent results suggest that their formation may have been more complex than previously thought, they still are the best approximation to a stellar population formed over a relatively short timescale (less than 1 Gyr) and with virtually no dispersion in the iron content. Indeed, only one cluster-like system (omega Centauri) in the Galactic halo is known to have multiple stellar populations with a significant spread in iron abundance and age. Similar findings in the Galactic bulge have been hampered by the obscuration arising from thick and varying layers of interstellar dust. Here we report that Terzan 5, a globular-cluster-like system in the Galactic bulge, has two stellar populations with different iron contents and ages. Terzan 5 could be the surviving remnant of one of the primordial building blocks that are thought to merge and form galaxy bulges.

The remnants of galaxy formation from a panoramic survey of the region around M31.

In hierarchical cosmological models, galaxies grow in mass through the continual accretion of smaller ones. The tidal disruption of these systems is expected to result in loosely bound stars surrounding the galaxy, at distances that reach 10-100 times the radius of the central disk. The number, luminosity and morphology of the relics of this process provide significant clues to galaxy formation history, but obtaining a comprehensive survey of these components is difficult because of their intrinsic faintness and vast extent. Here we report a panoramic survey of the Andromeda galaxy (M31). We detect stars and coherent structures that are almost certainly remnants of dwarf galaxies destroyed by the tidal field of M31. An improved census of their surviving counterparts implies that three-quarters of M31's satellites brighter than M(v) = -6 await discovery. The brightest companion, Triangulum (M33), is surrounded by a stellar structure that provides persuasive evidence for a recent encounter with M31. This panorama of galaxy structure directly confirms the basic tenets of the hierarchical galaxy formation model and reveals the shared history of M31 and M33 in the unceasing build-up of galaxies.

The spatial distribution of actin and mechanical cycle of myosin are different in right and left ventricles of healthy mouse hearts.

The contraction of the right ventricle (RV) expels blood into the pulmonary circulation, and the contraction of the left ventricle (LV) pumps blood into the systemic circulation through the aorta. The respective afterloads imposed on the LV and RV by aortic and pulmonary artery pressures create very different mechanical requirements for the two ventricles. Indeed, differences have been observed in the contractile performance between left and right ventricular myocytes in dilated cardiomyopathy, in congestive heart failure, and in energy usage and speed of contraction at light loads in healthy hearts. In spite of these functional differences, it is commonly believed that the right and left ventricular muscles are identical because there were no differences in stress development, twitch duration, work performance, or power among the RV and LV in dogs. This report shows that on a mesoscopic scale [when only a few molecules are studied (here three to six molecules of actin) in ex vivo ventricular myofibrils], the two ventricles in rigor differ in the degree of orientational disorder of actin within in filaments and during contraction in the kinetics of the cross-bridge cycle.

Functional outcomes following ankle arthrodesis in males with haemophilia: analyses using the CDC's Universal Data Collection surveillance project.

In persons with haemophilia (PWH), repeated ankle haemarthroses lead to pain, loss of joint range of motion (ROM), and limitations in activity and participation in society. PWH are offered ankle arthrodesis (AA) to eliminate pain. In our experience, PWH are hesitant to proceed to AA due to concerns regarding gait anomalies, functional decline and complete loss of ROM. The aim of this study was to report outcomes in ROM, assistive device (AD)/wheelchair use, activity scale and work/school absenteeism for participants in the CDC's Universal Data Collection surveillance project (UDC) pre- and post- AA. Males with haemophilia enrolled in the UDC with first report of AA (1998-2010) were selected. Descriptive statistics were calculated using data from the annual study visit pre-AA and the follow-up visit (~12-24 months) post-AA. The 68 subjects who fulfilled the criteria were: mean age 36.9 years (SD = 12.9); 85.3% white; 85.3% haemophilia A; 72% severe, 20.6% moderate; and 10.3% with inhibitor once during the study period. Mean loss in total arc of ankle motion was 17.02° (SD = 21.8, P ≤ 0.01) pre- compared to post-AA. For 61.8%, there was no change in use of AD for ambulation/mobility. For 85.3%, there was no change in use of a wheelchair. On a self-reported activity scale, 11.8% improved, 8.8% worsened and 79.4% did not change. Work/school absenteeism averaged 2.7 (SD = 6.4) pre- and 1.5 (SD = 6.4, P = 0.26) days per year post-AA. While ankle ROM was significantly reduced post-AA, for most subjects, there was no change in use of AD/wheelchair for ambulation/mobility. Physical activity was maintained and work/school absenteeism remained stable.

A turbulent wake as a tracer of 30,000 years of Mira's mass loss history.

Mira is one of the first variable stars ever discovered and it is the prototype (and also the nearest example) of a class of low-to-intermediate-mass stars in the late stages of stellar evolution. These stars are relatively common and they return a large fraction of their original mass to the interstellar medium (ISM) (ref. 2) through a processed, dusty, molecular wind. Thus stars in Mira's stage of evolution have a direct impact on subsequent star and planet formation in their host galaxy. Previously, the only direct observation of the interaction between Mira-type stellar winds and the ISM was in the infrared. Here we report the discovery of an ultraviolet-emitting bow shock and turbulent wake extending over 2 degrees on the sky, arising from Mira's large space velocity and the interaction between its wind and the ISM. The wake is visible only in the far ultraviolet and is consistent with an unusual emission mechanism whereby molecular hydrogen is excited by turbulent mixing of cool molecular gas and shock-heated gas. This wind wake is a tracer of the past 30,000 years of Mira's mass-loss history and provides an excellent laboratory for studying turbulent stellar wind-ISM interactions.

An ancient nova shell around the dwarf nova Z Camelopardalis.

Cataclysmic variables (classical novae and dwarf novae) are binary star systems in which a red dwarf transfers hydrogen-rich matter, by way of an accretion disk, to its white dwarf companion. In dwarf novae, an instability is believed to episodically dump much of the accretion disk onto the white dwarf. The liberation of gravitational potential energy then brightens these systems by up to 100-fold every few weeks or months. Thermonuclear-powered eruptions thousands of times more luminous occur in classical novae, accompanied by significant mass ejection and formation of clearly visible shells from the ejected material. Theory predicts that the white dwarfs in all dwarf novae must eventually accrete enough mass to undergo classical nova eruptions. Here we report a shell, an order of magnitude more extended than those detected around many classical novae, surrounding the prototypical dwarf nova Z Camelopardalis. The derived shell mass matches that of classical novae, and is inconsistent with the mass expected from a dwarf nova wind or a planetary nebula. The shell observationally links the prototypical dwarf nova Z Camelopardalis with an ancient nova eruption and the classical nova process.

Transiting extrasolar planetary candidates in the Galactic bulge.

More than 200 extrasolar planets have been discovered around relatively nearby stars, primarily through the Doppler line shifts owing to reflex motions of their host stars, and more recently through transits of some planets across the faces of the host stars. The detection of planets with the shortest known periods, 1.2-2.5 days, has mainly resulted from transit surveys which have generally targeted stars more massive than 0.75 M(o), where M(o) is the mass of the Sun. Here we report the results from a planetary transit search performed in a rich stellar field towards the Galactic bulge. We discovered 16 candidates with orbital periods between 0.4 and 4.2 days, five of which orbit stars of masses in the range 0.44-0.75 M(o). In two cases, radial-velocity measurements support the planetary nature of the companions. Five candidates have orbital periods below 1.0 day, constituting a new class of ultra-short-period planets, which occur only around stars of less than 0.88 M(o). This indicates that those orbiting very close to more-luminous stars might be evaporatively destroyed or that jovian planets around stars of lower mass might migrate to smaller radii.

Suppression of star formation in early-type galaxies by feedback from supermassive black holes.

Detailed high-resolution observations of the innermost regions of nearby galaxies have revealed the presence of supermassive black holes. These black holes may interact with their host galaxies by means of 'feedback' in the form of energy and material jets; this feedback affects the evolution of the host and gives rise to observed relations between the black hole and the host. Here we report observations of the ultraviolet emissions of massive early-type galaxies. We derive an empirical relation for a critical black-hole mass (as a function of velocity dispersion) above which the outflows from these black holes suppress star formation in their hosts by heating and expelling all available cold gas. Supermassive black holes are negligible in mass compared to their hosts but nevertheless seem to play a critical role in the star formation history of galaxies.

Regulatory mechanisms in cell-mediated immune responses. III. I-region control of suppressor cell interaction with responder cells in mixed lymphocyte reactions.

Active suppression of mixed lymphocyte reaction (MLR) response is mediated by a soluble factor released by alloantigen-activated murine suppressor cells. Genetic restrictions controlling suppressor factor interaction with MLR responder cells were elucidated in this study. Non-H-2 genetic background was irrelevant to effective interaction. Using congenic strains and strains with intra-H-2 recombinants the genetic locus controlling suppressor T-cell-responder cell interaction was mapped in the I-C or S regions of the H-2 complex. Similarly, recombinant strains were used to exclude the presence of another suppressor cell-responder cell interaction locus in K,I-A, and I-B regions. It thus appears that the I-C subregion of the H-2 complex controls suppressive cell interactions in this T-cell-mediated immune response.