Flow Direction-Dependent Elastic Instability in a Symmetry-Breaking Microchannel

This paper reports flow direction-dependent elastic instability in a symmetry-breaking microchannel. The microchannel consisted of a square chamber and a nozzle structure. A viscoelastic polyacrylamide solution was used for the instability demonstration. The instability was realized as the viscoelastic flow became asymmetric and unsteady in the microchannel when the flow exceeded a critical Weissenberg number. The critical Weissenberg number was found to be different for the forward-directed flow and the backward-directed flow in the microchannel.

The signature of charge dependent directed flow observables by electromagnetic fields in heavy ion collisions

We discuss the generation of the directed flow $$v_1(p_T,y_z)$$ v 1 ( p T , y z ) induced by the electromagnetic field as a function of $$p_T$$ p T and $$y_z$$ y z . Despite the complex dynamics of charged particles due to strong interactions generating several anisotropies in the azimuthal angle, it is possible at $$p_T > m$$ p T > m to directly correlate the splitting in $$v_1$$ v 1 of heavy quarks with different charges to some main features of the magnetic field, and in particular its values at formation and freeze-out time. We further found that the slope of the splitting $$d\Delta v_1/dy_z|_{y_z=0}$$ d Δ v 1 / d y z | y z = 0 of positively and negatively charged particles at high $$p_T$$ p T can be formulated as $$d\Delta v_1/dy_z|_{y_z=0}=-\alpha \frac{\partial \ln f}{\partial p_T}+\frac{2\alpha -\beta }{p_T}$$ d Δ v 1 / d y z | y z = 0 = - α ∂ ln f ∂ p T + 2 α - β p T , where f is the $$p_T$$ p T spectra of the charged particles and the constants $$\alpha $$ α and $$\beta $$ β (order of MeV) are constrained by the y component of magnetic fields and the sign of $$\alpha $$ α is simply determined by the difference $$\Delta [tB_y(t)]$$ Δ [ t B y ( t ) ] in the center of colliding systems at the formation time of particles and at the time when particles leave the effective range of electromagnetic fields or freeze out. The formula is derived from general considerations and is confirmed by several related numerical simulations; it supplies a useful guide to quantify the effect of different magnetic field configurations and provides an evidence of why the measurement of $$\Delta v_1$$ Δ v 1 of charm, bottom and leptons from $$Z^0$$ Z 0 decay and their correlations are a powerful probe of the initial e.m. fields in ultra-relativistic collisions.

CBM Performance for Λ Hyperon Directed Flow Measurements in Au + Au Collisions at 12A GeV/c

We present the current status of the performance studies of Λ hyperon directed flow measurement with the CBM experiment at the future FAIR facility in Darmstadt. Kalman Filter mathematics is used to reconstruct Λ→pπ− weak decay kinematics, while the Particle Finder Simple package is used to optimize criteria for Λ hyperon candidate selection. Directed flow of Λ hyperons is studied as a function of rapidity, transverse momentum and collision centrality. The effects on flow measurement due to non-uniformity of the CBM detector response in the azimuthal angle, transverse momentum and rapidity are corrected using the QnTools analysis framework.

Early turbulence and pulsatile flows enhance diodicity of Tesla’s macrofluidic valve

Microfluidics has enabled a revolution in the manipulation of small volumes of fluids. Controlling flows at larger scales and faster rates, or macrofluidics, has broad applications but involves the unique complexities of inertial flow physics. We show how such effects are exploited in a device proposed by Nikola Tesla that acts as a diode or valve whose asymmetric internal geometry leads to direction-dependent fluidic resistance. Systematic tests for steady forcing conditions reveal that diodicity turns on abruptly at Reynolds number $${\rm{Re}}\approx 200$$ Re ≈ 200 and is accompanied by nonlinear pressure-flux scaling and flow instabilities, suggesting a laminar-to-turbulent transition that is triggered at unusually low $${\rm{Re}}$$ Re . To assess performance for unsteady forcing, we devise a circuit that functions as an AC-to-DC converter, rectifier, or pump in which diodes transform imposed oscillations into directed flow. Our results confirm Tesla’s conjecture that diodic performance is boosted for pulsatile flows. The connections between diodicity, early turbulence and pulsatility uncovered here can inform applications in fluidic mixing and pumping.

Effect of Nonreciprocal Forces on the Stability of Dust Clusters

Results are presented from studies of the stability of the plane dust clusters in the form of a regular polygon with the number of particles from two to five. It is assumed that the particles are placed in the plasma consisting of Maxwellian electrons and a directed flow of cold ions. It is shown that, in such clusters, the oscillatory instabilities can develop along with the aperiodic instabilities. The ranges of plasma parameters are determined, within which the oscillatory instability of the five-particle cluster becomes saturated at the weakly nonlinear stage. As a result, the cluster forms a time crystal, which can be a chiral crystal.