Primary and secondary intrusions in double-diffusively stable vertical gradients

The purpose of this paper is to show that molecularly-driven double-diffusive intrusions can produce significant lateral and vertical double-diffusive mixing even when the initial temperature and salinity are both stably stratified in the vertical. Assuming uniform density-compensated horizontal gradients and periodic disturbances, three-dimensional direct numerical simulations (DNS) for the fastest growing intrusion show that the latter equilibrates due to the generation of salt fingers which reduce the driving buoyancy pressure gradient. The DNS also provided statistical data for a new parameterization of the salt finger fluxes which includes the effects of shear and variable vertical gradients. This parameterization makes it feasible to numerically investigate the subharmonic instabilities of the equilibrium DNS solution. Linearized calculations with parameterized salt fingers show that the vertical and horizontal wavelength of the fastest growing secondary instability are approximately three and fourteen times that of the primary intrusion. Nonlinear simulations show that the equilibrium lateral and vertical double-diffusive fluxes of the secondary mode are an order of magnitude larger than those of the primary intrusion. Numerically determined dependences of the intrusion lateral velocity on the vertical wavelength are compared to previous numerical and experimental work

Direct Numerical Simulation of 3D Salt Fingers: From Secondary Instability to Chaotic Convection

The amplification and equilibration of three-dimensional salt fingers in unbounded uniform vertical gradients of temperature and salinity is modeled with a Direct Numerical Simulation in a triply periodic computational domain. A fluid dynamics video of the simulation shows that the secondary instability of the fastest growing square-planform finger mode is a combination of the well-known vertical shear instability of two-dimensional fingers [Holyer, 1984] and a new horizontal shear mode.Comment: APS DFD Gallery of Fluid Motion 200

River Discharge and Bathymetry Estimation from Inversion of Surface Currents and Water Surface Elevation Observations

The article of record as published may be found at https://doi.org/10.1175/JTECH-D-18-0055.1We developed an approach for estimating river discharge and water depth from measurements of surfacevelocity and water surface elevation, based on analytical velocity–depth and velocity–slope relationships derived from the steady gravity–friction momentum balance and mass conservation. A key component in this approach is specifying the influence of bottom friction on the modeled depth-averaged flow. Accordingly, we considered two commonly used bottom friction parameterizations—a depth-independent Darcy friction coefficient and a depth-dependent friction coefficient based on the Manning’s roughness parameter. As- suming that the bottom friction coefficient is known, the unknown discharge was determined by minimizing the difference between the measured total head profile and the one determined from the velocity–slope relationship. The model performance and its sensitivity to key assumptions were evaluated using existing bathymetry data, and surface velocity and elevation observations obtained during field experiments on the Kootenai River near Bonners Ferry, Idaho, and the Hanford reach of the Columbia River. We found that the Manning’s friction parameterization provided superior depth and discharge estimates, compared to the Darcy friction law. For both steady and moderately unsteady flow, inversions based on the Manning’s friction provided discharge and thalweg depth estimates with relative errors not exceeding 5% and 12%, respectively

The Mechanical Properties of Drosophila Jump Muscle Expressing Wild-Type and Embryonic Myosin Isoforms

Transgenic Drosophila are highly useful for structure-function studies of muscle proteins. However, our ability to mechanically analyze transgenically expressed mutant proteins in Drosophila muscles has been limited to the skinned indirect flight muscle preparation. We have developed a new muscle preparation using the Drosophila tergal depressor of the trochanter (TDT or jump) muscle that increases our experimental repertoire to include maximum shortening velocity (Vslack), force-velocity curves and steady-state power generation; experiments not possible using indirect flight muscle fibers. When transgenically expressing its wild-type myosin isoform (Tr-WT) the TDT is equivalent to a very fast vertebrate muscle. TDT has a Vslack equal to 6.1 ± 0.3 ML/s at 15°C, a steep tension-pCa curve, isometric tension of 37 ± 3 mN/mm2, and maximum power production at 26% of isometric tension. Transgenically expressing an embryonic myosin isoform in the TDT muscle increased isometric tension 1.4-fold, but decreased Vslack 50% resulting in no significant difference in maximum power production compared to Tr-WT. Drosophila expressing embryonic myosin jumped <50% as far as Tr-WT that, along with comparisons to frog jump muscle studies, suggests fast muscle shortening velocity is relatively more important than high tension generation for Drosophila jumping

Two-particle transverse momentum correlations in pp and p-Pb collisions at energies available at the CERN Large Hadron Collider

Two-particle transverse momentum differential correlators, recently measured in Pb-Pb collisions at LHC energies, provide an additional tool to gain insights into particle production mechanisms and infer transport properties, such as the ratio of shear viscosity to entropy density, of the medium created in Pb-Pb collisions. The longitudinal long-range correlations and the large azimuthal anisotropy measured at low transverse momenta in small collision systems, namely pp and p-Pb, at LHC energies resemble manifestations of collective behaviour. This suggests that locally equilibrated matter may be produced in these small collision systems, similar to what is observed in Pb-Pb collisions. In this work, the same two-particle transverse momentum differential correlators are exploited in pp and p-Pb collisions at s√=7 TeV and sNN−−−√=5.02 TeV, respectively, to seek evidence for viscous effects. Specifically, the strength and shape of the correlators are studied as a function of the produced particle multiplicity to identify evidence for longitudinal broadening that might reveal the presence of viscous effects in these smaller systems. The measured correlators and their evolution from pp and p-Pb to Pb-Pb collisions are additionally compared to predictions from Monte Carlo event generators, and the potential presence of viscous effects is discussed

Investigation of K+K− interactions via femtoscopy in Pb-Pb collisions at √sNN = 2.76 TeV at the CERN Large Hadron Collider

Femtoscopic correlations of non-identical charged kaons (K+K−) are studied in Pb−Pb collisions at a center-of-mass energy per nucleon−nucleon collision sNN−−−√=2.76 TeV by ALICE at the LHC. One-dimensional K+K− correlation functions are analyzed in three centrality classes and eight intervals of particle-pair transverse momentum. The Lednický and Luboshitz interaction model used in the K+K− analysis includes the final-state Coulomb interactions between kaons and the final-state interaction through a0(980) and f0(980) resonances. The mass of f0(980) and coupling were extracted from the fit to K+K− correlation functions using the femtoscopic technique for the first time. The measured mass and width of the f0(980) resonance are consistent with other published measurements. The height of the ϕ(1020) meson peak present in the K+K− correlation function rapidly decreases with increasing source radius, qualitatively in agreement with an inverse volume dependence. A phenomenological fit to this trend suggests that the ϕ(1020) meson yield is dominated by particles produced directly from the hadronization of the system. The small fraction subsequently produced by FSI could not be precisely quantified with data presented in this paper and will be assessed in future work

Σ(1385)± resonance production in Pb–Pb collisions at √sNN = 5.02 TeV

Hadronic resonances are used to probe the hadron gas produced in the late stage of heavy-ion collisions since they decay on the same timescale, of the order of 1 to 10 fm/c, as the decoupling time of the system. In the hadron gas, (pseudo)elastic scatterings among the products of resonances that decayed before the kinetic freeze-out and regeneration processes counteract each other, the net effect depending on the resonance lifetime, the duration of the hadronic phase, and the hadronic cross sections at play. In this context, the Σ(1385)± particle is of particular interest as models predict that regeneration dominates over rescattering despite its relatively short lifetime of about 5.5 fm/c. The first measurement of the Σ(1385)± resonance production at midrapidity in Pb-Pb collisions at sNN−−−√=5.02 TeV with the ALICE detector is presented in this Letter. The resonances are reconstructed via their hadronic decay channel, Λπ, as a function of the transverse momentum (pT) and the collision centrality. The results are discussed in comparison with the measured yield of pions and with expectations from the statistical hadronization model as well as commonly employed event generators, including PYTHIA8/Angantyr and EPOS3 coupled to the UrQMD hadronic cascade afterburner. None of the models can describe the data. For Σ(1385)±, a similar behaviour as K∗(892)0 is observed in data unlike the predictions of EPOS3 with afterburner

Measurement of ψ (2S) production as a function of charged-particle pseudorapidity density in pp collisions at √s = 13 TeV and p–Pb collisions at √sNN = 8.16 TeV with ALICE at the LHC

Production of inclusive charmonia in pp collisions at center-of-mass energy of √s = 13 TeV and p–Pb collisions at center-of-mass energy per nucleon pair of √sNN = 8.16 TeV is studied as a function of charged-particle pseudorapidity density with ALICE. Ground and excited charmonium states (J/ψ, ψ(2S)) are measured from their dimuon decays in the interval of rapidity in the center-of-mass frame 2.5 < ycms < 4.0 for pp collisions, and 2.03 < ycms < 3.53 and −4.46 < ycms < −2.96 for p–Pb collisions. The charged-particle pseudorapidity density is measured around midrapidity (|η| < 1.0). In pp collisions, the measured charged-particle multiplicity extends to about six times the average value, while in p-Pb collisions at forward (backward) rapidity a multiplicity corresponding to about three (four) times the average is reached. The ψ(2S) yield increases with the charged-particle pseudorapidity density. The ratio of ψ(2S) over J/ψ yield does not show a significant multiplicity dependence in either colliding system, suggesting a similar behavior of J/ψ and ψ(2S) yields with respect to charged-particle pseudorapidity density. Results for the ψ(2S) yield and its ratio with respect to J/ψ agree with available model calculations