298 research outputs found
The measurement of the material parameters of viscoelastic fluids using a rotating sphere and a rheogoniometer
ΠΠΎΠ½ΡΠ΅ΠΏΡ "Π·Π½Π°Π½ΠΈΠ΅" Π² ΡΠΎΡΡΠ°Π²Π΅ ΡΠ΅ΡΠ΅Π²ΠΎΠ³ΠΎ ΠΆΠ°Π½ΡΠ° "ΠΠΈΡΡΠΈΡ ΡΠ½ΠΈΠ²Π΅ΡΡΠΈΡΠ΅ΡΠ°"
ΠΡΠ΅Π΄Π»Π°Π³Π°Π΅ΡΡΡ Π΄Π΅ΡΠΈΠ½ΠΈΡΠΈΡ ΡΠ΅ΡΠ΅Π²ΠΎΠ³ΠΎ ΠΆΠ°Π½ΡΠ° "ΠΠΈΡΡΠΈΡ ΡΠ½ΠΈΠ²Π΅ΡΡΠΈΡΠ΅ΡΠ°". ΠΠΏΡΠ΅Π΄Π΅Π»ΡΡΡΡΡ ΠΎΡΠΎΠ±Π΅Π½Π½ΠΎΡΡΠΈ Π²Π΅ΡΠ±Π°Π»ΠΈΠ·Π°ΡΠΈΠΈ ΠΊΠΎΠ½ΡΠ΅ΠΏΡΠ° "Π·Π½Π°Π½ΠΈΠ΅" Π½Π° ΠΌΠ°ΡΠ΅ΡΠΈΠ°Π»Π΅ Π°Π½Π°Π»ΠΈΠ·Π° 30 ΠΌΠΈΡΡΠΈΠΉ Π²Π΅Π΄ΡΡΠΈΡ
ΡΠ½ΠΈΠ²Π΅ΡΡΠΈΡΠ΅ΡΠΎΠ² (ΠΏΠΎ Π΄Π°Π½Π½ΡΠΌ "ΠΠ°ΡΠΈΠΎΠ½Π°Π»ΡΠ½ΠΎΠ³ΠΎ ΡΠ΅ΠΉΡΠΈΠ½Π³Π° ΡΠΎΡΡΠΈΠΉΡΠΊΠΈΡ
Π²ΡΠ·ΠΎΠ²")
Metamagnetism in the 2D Hubbard Model with easy axis
Although the Hubbard model is widely investigated, there are surprisingly few
attempts to study the behavior of such a model in an external magnetic field.
Using the Projector Quantum Monte Carlo technique, we show that the Hubbard
model with an easy axis exhibits metamagnetic behavior if an external field is
turned on. For the case of intermediate correlations strength , we observe a
smooth transition from an antiferromagnetic regime to a paramagnetic phase.
While the staggered magnetization will decrease linearly up to a critical field
, uniform magnetization develops only for fields higher than .Comment: RevTeX 5 pages + 2 postscript figures (included), accepted for PRB
Rapid Communication
Thixotropy in macroscopic suspensions of spheres
An experimental study of the viscosity of a macroscopic suspension, i.e. a
suspension for which Brownian motion can be neglected, under steady shear is
presented. The suspension is prepared with a high packing fraction and is
density-matched in a Newtonian carrier fluid. The viscosity of the suspension
depends on the shear rate and the time of shearing. It is shown for the first
time that a macroscopic suspension shows thixotropic viscosity, i.e.
shear-thinning with a long relaxation time as a unique function of shear. The
relaxation times show a systematic decrease with increasing shear rate. These
relaxation times are larger when decreasing the shear rates, compared to those
observed after increasing the shear. The time scales involved are about 10000
times larger than the viscous time scale and about 1000 times smaller than the
thermodynamic time scale. The structure of the suspension at the outer cylinder
of a viscometer is monitored with a camera, showing the formation of a
hexagonal structure. The temporal decrease of the viscosity under shear
coincides with the formation of this hexagonal pattern
Convective Nonlinearity in Non-Newtonian Fluids
In the limit of infinite yield time for stresses, the hydrodynamic equations
for viscoelastic, Non-Newtonian liquids such as polymer melts must reduce to
that for solids. This piece of information suffices to uniquely determine the
nonlinear convective derivative, an ongoing point of contention in the rheology
literature.Comment: 4 page
Solitary coherent structures in viscoelastic shear flow: computation and mechanism
Starting from stationary bifurcations in Couette-Dean flow, we compute
nontrivial stationary solutions in inertialess viscoelastic circular Couette
flow. These solutions are strongly localized vortex pairs, exist at arbitrarily
large wavelengths, and show hysteresis in the Weissenberg number, similar to
experimentally observed ``diwhirl'' patterns. Based on the computed velocity
and stress fields, we elucidate a heuristic, fully nonlinear mechanism for
these flows. We propose that these localized, fully nonlinear structures
comprise fundamental building blocks for complex spatiotemporal dynamics in the
flow of elastic liquids.Comment: 5 pages text and 4 figures. Submitted to Physical Review Letter
A computer-controlled four-roll mill for investigations of particle and drop dynamics in two-dimensional linear shear flows
Elastic turbulence in curvilinear flows of polymer solutions
Following our first report (A. Groisman and V. Steinberg, \sl Nature , 53 (2000)) we present an extended account of experimental observations of
elasticity induced turbulence in three different systems: a swirling flow
between two plates, a Couette-Taylor (CT) flow between two cylinders, and a
flow in a curvilinear channel (Dean flow). All three set-ups had high ratio of
width of the region available for flow to radius of curvature of the
streamlines. The experiments were carried out with dilute solutions of high
molecular weight polyacrylamide in concentrated sugar syrups. High polymer
relaxation time and solution viscosity ensured prevalence of non-linear elastic
effects over inertial non-linearity, and development of purely elastic
instabilities at low Reynolds number (Re) in all three flows. Above the elastic
instability threshold, flows in all three systems exhibit features of developed
turbulence. Those include: (i)randomly fluctuating fluid motion excited in a
broad range of spatial and temporal scales; (ii) significant increase in the
rates of momentum and mass transfer (compared to those expected for a steady
flow with a smooth velocity profile). Phenomenology, driving mechanisms, and
parameter dependence of the elastic turbulence are compared with those of the
conventional high Re hydrodynamic turbulence in Newtonian fluids.Comment: 23 pages, 26 figure
On the performance of enhanced constitutive models for polymer melts in a cross-slot flow
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