arXiv subjects

Jonathan I. Katz

Publications and source records attributed to Jonathan I. Katz.

6 recordsLinked to original sources

arXiv2026

Transient X-ray Sources as Extremely Eccentric Mass-Transfer Binaries with Compact Companions

It has long been suggested that X-ray transients are produced at periastron of stellar-compact object binaries with eccentric orbits. Recoil of matter evaporated from the star by X-rays from matter transferred at periastron increases the orbital semi-major axis and eccentricity. After periastrons the object would be a transient X-ray source, a Galactic analogue of a tidal disruption event (TDE), but recurrent with a gradually increasing period rather than catastrophic.

astro-ph.HE↗

arXiv2024

Jupiter Mass Binaries and Cosmic Ray Viscosity

The fraction of planetary mass objects in the Trapezium cluster that are in wide binaries is much greater than implied by extrapolation to lower masses of the fraction of stars that are in wide binaries. Wide binaries may be produced by gravitational collapse of a medium with fluid vorticity. In a uniform medium with uniform vorticity the collapse criterion is independent of the size and mass of the collapsing region, which would imply a wide binary fraction independent of mass, in contradiction to observation. Angular momentum, rather than thermal pressure, may be the chief obstacle to star formation. The excess of Jupiter Mass Binary Objects in the Trapezium cluster may be attributed to cosmic ray viscosity that transports angular momentum to surrounding material. Viscosity is more effective in smaller and less massive collapsing regions, preferentially producing planetary mass wide binaries. Energetic particles trapped on magnetic field lines in a corona contribute to viscosity, dissipation and angular momentum flow in accretion discs.

astro-ph.GA↗

arXiv2014

Rheology in the Teaching Lab: Properties of Starch Suspensions

In everyday life we encounter many complex fluids, from shear-thinning paint and toothpaste to shear-thickening starch suspensions. The study of their properties offers an opportunity for students to relate sophisticated physical concepts to their everyday experience. Modern rheology uses expensive equipment impractical for the teaching laboratory. Here we describe a rudimentary rheometer suitable for student laboratories that can demonstrate and quantify discontinuous shear thickening, the most dramatic property of complex fluids, and use it to measure the properties of starch suspensions.

physics.ed-ph↗

arXiv2014

Hysteresis and Lubrication in Shear Thickening of Cornstarch Suspensions

Aqueous and brine suspensions of corn starch show striking discontinuous shear thickening. We have found that a suspension shear-thickened throughout may remain in the jammed thickened state as the strain rate is reduced, but an unjamming front may propagate from any unjammed regions. Transient shear thickening is observed at strain rates below the thickening threshold, and above it the stress fluctuates. The jammed shear-thickened state may persist to low strain rates, with stresses resembling sliding friction and effective viscosity inversely proportional to the strain rate. At the thickening threshold fluid pressure depins the suspension's contact lines on solid boundaries so that it slides, shears, dilates and jams. In oil suspensions lubrication and complete wetting of confining surfaces eliminate contact line forces and prevent jamming and shear thickening, as does addition of immiscible liquid surfactant to brine suspensions. Starch suspensions in glycerin-water solutions, viscous but incompletely wetting, have intermediate properties.

cond-mat.soft↗

arXiv2013

Ultrasonic Attenuation and Speed of Sound of Cornstarch Suspensions

The goal of this study is to contribute to the physics underlying the material properties of suspensions that exhibit shear thickening through the ultrasonic characterization of suspensions of cornstarch in a density-matched solution. Ultrasonic measurements at frequencies in the range of 4 to 8 MHz of the speed of sound and the frequency-dependent attenuation properties are reported for concentrations of cornstarch in a density-matched aqueous (cesium chloride brine) suspension, ranging up to 40% cornstarch. The speed of sound is found to range from 1483 +/- 10 m/s in pure brine to 1765 +/- 9 m/s in the 40% cornstarch suspension. The bulk modulus of a granule of cornstarch is inferred to be (1.2 +/- 0.1) X 10^{10} Pa. The attenuation coefficient at 5 MHz increases from essentially zero in brine to 12.0 +/- 1.2 dB/cm at 40% cornstarch.

physics.chem-ph↗

arXiv2000

Low Frequency Radio Pulses from Gamma-Ray Bursts?

Gamma-ray bursts, if they are generated in the process of interaction between relativistic strongly magnetized winds and an ambient medium, may be accompanied by very short pulses of low-frequency radio emission. The bulk of this emission is expected to be at the frequencies of $\sim 0.1-1$ MHz and cannot be observed. However, the high-frequency tail of the low-frequency radio emission may reach a few ten MHz and be detected, especially if the strength of the magnetic field of the wind is extremely high.

astro-ph↗