3,699 research outputs found
Observing mergers of non-spinning black-hole binaries
Advances in the field of numerical relativity now make it possible to
calculate the final, most powerful merger phase of binary black-hole
coalescence for generic binaries. The state of the art has advanced well beyond
the equal-mass case into the unequal-mass and spinning regions of parameter
space. We present a study of the nonspinning portion of parameter space,
primarily using an analytic waveform model tuned to available numerical data,
with an emphasis on observational implications. We investigate the impact of
varied mass ratio on merger signal-to-noise ratios (SNRs) for several
detectors, and compare our results with expectations from the test-mass limit.
We note a striking similarity of the waveform phasing of the merger waveform
across the available mass ratios. Motivated by this, we calculate the match
between our 1:1 (equal mass) and 4:1 mass-ratio waveforms during the merger as
a function of location on the source sky, using a new formalism for the match
that accounts for higher harmonics. This is an indicator of the amount of
degeneracy in mass ratio for mergers of moderate-mass-ratio systems.Comment: 13 pages, 11 figures, submitted to Phys. Rev.
Renovation Can Double Pasture Production
Renovation is often recommended as the best method for improving pastures. Results of long-time studies are now available where renovated pastures have been compared with unimproved pastures in southern Iowa
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The Coherent Structures of Shallowwater Turbulence: Deformationradius Effects, Cyclone/Anticyclone Asymmetry and Gravitywave Generation
Over a large range of Rossby and Froude numbers, we investigate the dynamics of initially balanced decaying turbulence in a shallow rotating fluid layer. As in the case of incompressible two‐dimensional decaying turbulence, coherent vortex structures spontaneously emerge from the initially random flow. However, owing to the presence of a free surface, a wealth of new phenomena appear in the shallow‐water system. The upscale energy cascade, common to strongly rotating flows, is arrested by the presence of a finite Rossby deformation radius. Moreover, in contrast to near‐geostrophic dynamics, a strong asymmetry is observed to develop as the Froude number is increased, leading to a clear dominance of anticyclonic vortices over cyclonic ones, even though no β effect is present in the system. Finally, we observe gravity waves to be generated around the vortex structures, and, in the strongest cases, they appear in the form of shocks. We briefly discuss the relevance of this study to the vortices observed in Jupiter’s atmosphere
Large-Scale Magnetic-Field Generation by Randomly Forced Shearing Waves
A rigorous theory for the generation of a large-scale magnetic field by
random non-helically forced motions of a conducting fluid combined with a
linear shear is presented in the analytically tractable limit of low Rm and
weak shear. The dynamo is kinematic and due to fluctuations in the net
(volume-averaged) electromotive force. This is a minimal proof-of-concept
quasilinear calculation aiming to put the shear dynamo, a new effect recently
found in numerical experiments, on a firm theoretical footing. Numerically
observed scalings of the wavenumber and growth rate of the fastest growing
mode, previously not understood, are derived analytically. The simplicity of
the model suggests that shear dynamo action may be a generic property of
sheared magnetohydrodynamic turbulence.Comment: Paper substantially rewritten, results changed (relative to v1).
Revised versio
Modeling kicks from the merger of generic black-hole binaries
Recent numerical relativistic results demonstrate that the merger of
comparable-mass spinning black holes has a maximum ``recoil kick'' of up to
\sim 4000 \kms. However the scaling of these recoil velocities with mass
ratio is poorly understood. We present new runs showing that the maximum
possible kick perpendicular to the orbital plane does not scale as
(where is the symmetric mass ratio), as previously proposed, but is more
consistent with , at least for systems with low orbital precession.
We discuss the effect of this dependence on galactic ejection scenarios and
retention of intermediate-mass black holes in globular clusters.Comment: 5 pages, 1 figure, 3 tables. Version published in Astrophys. J. Let
Unilateral total hip replacement patients with symptomatic leg length inequality have abnormal hip biomechanics during walking
BACKGROUND
Symptomatic leg length inequality accounts for 8.7% of total hip replacement related claims made against the UK National Health Service Litigation authority. It has not been established whether symptomatic leg length inequality patients following total hip replacement have abnormal hip kinetics during gait.
METHODS
Hip kinetics in 15 unilateral total hip replacement patients with symptomatic leg length inequality during gait was determined through multibody dynamics and compared to 15 native hip healthy controls and 15 'successful' asymptomatic unilateral total hip replacement patients.
FINDING
More significant differences from normal were found in symptomatic leg length inequality patients than in asymptomatic total hip replacement patients. The leg length inequality patients had altered functions defined by lower gait velocity, reduced stride length, reduced ground reaction force, decreased hip range of motion, reduced hip moment and less dynamic hip force with a 24% lower heel-strike peak, 66% higher mid-stance trough and 37% lower toe-off peak. Greater asymmetry in hip contact force was also observed in leg length inequality patients.
INTERPRETATION
These gait adaptions may affect the function of the implant and other healthy joints in symptomatic leg length inequality patients. This study provides important information for the musculoskeletal function and rehabilitation of symptomatic leg length inequality patients
Connections between Non-Rotating, Slowly Rotating, and Rapidly Rotating Turbulent Convection Transport Scalings
Buoyancy-driven convection is likely the dominant driver of turbulent motions
in the universe, and thus, is widely studied by physicists, engineers,
geophysicists and astrophysicists. Maybe unsurprisingly, these different
communities discuss the gross convective behaviors in different ways, often
without significant cross-talk existing between them. Here, we seek to draw
connections between these communities. We do so by carrying out a set of basic
scale estimations for how heat and fluid momentum transport should behave in
non-rotating, slowly rotating and rapidly rotating buoyancy-driven convective
environments. We find that slowly and rapidly rotating scalings can be
inter-related via one parameter, the so-called convective Rossby number \RoC,
a dissipation-free parameter measuring the importance of buoyancy driving
relative to rotation. Further, we map between non-flux-based and the
flux-based, buoyancy-driven scalings used by different groups. In doing so,
these scalings show that there are clean connections between the different
communities' approaches and that a number of the seemingly different scalings
are actually synonymous with one another.Comment: 15 pages, 3 figures, 2 Table
Lithofacies Control in Detrital Zircon Provenance Studies: Insights from the Cretaceous Methow Basin, Southern Canadian Cordillera
High-frequency sampling for detrital zircon analysis can provide a detailed record of fine-scale basin evolution by revealing the temporal and spatial variability of detrital zircon ages within clastic sedimentary successions. This investigation employed detailed sampling of two sedimentary successions in the Methow/Methow-Tyaughton basin of the southern Canadian Cordillera to characterize the heterogeneity of detrital zircon signatures within single lithofacies and assess the applicability of detrital zircon analysis in distinguishing fine-scale provenance changes not apparent in lithologic analysis of the strata. The Methow/Methow-Tyaughton basin contains two distinct stratigraphic sequences of middle Albian to Santonian clastic sedimentary rocks: submarine-fan deposits of the Harts Pass Formation/Jackass Mountain Group and fluvial deposits of the Winthrop Formation. Although both stratigraphic sequences displayed consistent ranges in detrital zircon ages on a broad scale, detailed sampling within each succession revealed heterogeneity in the detrital zircon age distributions that was systematic and predictable in the turbidite succession but unpredictable in the fluvial succession. These results suggest that a high-density sampling approach permits interpretation of fine-scale changes within a lithologically uniform turbiditic sedimentary succession, but heterogeneity within fluvial systems may be too large and unpredictable to permit accurate fine-scale characterization of the evolution of source regions. The robust composite detrital zircon age signature developed for these two successions permits comparison of the Methow/Methow-Tyaughton basin age signature with known plutonic source-rock ages from major plutonic belts throughout the Cretaceous North American margin. The Methow/Methow-Tyaughton basin detrital zircon age signature matches best with source regions in the southern Canadian Cordillera, requiring that the basin developed in close proximity to the southern Canadian Cordillera and providing evidence against large-scale dextral translation of the Methow terrane
Scoping review: Scope of practice of nurse-led services and access to care for people experiencing homelessness.
AIMS: To investigate the scope of practice of nurse-led services for people experiencing homelessness, and the influence on access to healthcare. DESIGN: A scoping review. DATA SOURCES: On 20 November 2020, the following databases were searched: CINAHL, Embase, MEDLINE, PubMed and Scopus. REVIEW METHODS: Included studies focused on people experiencing homelessness aged 18 years and over, nurse-led services in any setting and described the nursing scope of practice. Studies were peer-reviewed primary research, published in English from the year 2000. Three authors performed quality appraisals using the mixed methods assessment tool. Results were synthesized and discussed narratively and reported according to the PRISMA-ScR 2020 Statement. RESULTS: Nineteen studies were included from the United States (n = 9), Australia (n = 4), United Kingdom (n = 4) and Canada (n = 2). The total participant sample size was n = 6303. Studies focused on registered nurses (n = 10), nurse practitioners (n = 5) or both (n = 4), in outpatient or community settings. The nursing scope of practice was broad and covered a range of skills, knowledge and attributes. Key skills identified include assessment and procedural skills, client support and health education. Key attributes were a trauma-informed approach and building trust through communication. Important knowledge included understanding the impact of homelessness, knowledge of available services and the capacity to undertake holistic assessments. Findings suggest that nurse-led care facilitated access to healthcare through building trust and supporting clients to access services. CONCLUSION: Optimized nursing scope of practice can facilitate access to healthcare for people experiencing homelessness. Key factors in enabling this include autonomy in nursing practice, organizational support and education. IMPACT: The broad range of skills, knowledge and attributes reported provide a foundation from which to design an educational framework to optimize the nursing scope of practice, thereby increasing access to healthcare for people experiencing homelessness
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