11,522 research outputs found
Photonic measurements of the longitudinal expansion dynamics in Heavy-Ion collisions
Due to the smallness of the electromagnetic coupling, photons escape from the
hot and dense matter created in an heavy-ion collision at all times, in
contrast to hadrons which are predominantly emitted in the final freeze-out
phase of the evolving system. Thus, the thermal photon yield carries an imprint
from the early evolution. We suggest how this fact can be used to gain
information about where between the two limiting cases of Bjorken
(boost-invariant expansion) and Landau (complete initial stopping and
re-expansion) hydrodynamics the actual evolution can be found. We argue that
both the rapidity dependence of the photon yield and photonic HBT radii are
capable of answering this question.Comment: 10 pages, 3 figure
A predictive phenomenological tool at small Bjorken-x
We present the results from global fits of inclusive DIS experimental data
using the Balitsky-Kovchegov equation with running coupling.Comment: 5 pages, 2 figures, prepared for the Proceedings of 'Hot Quarks 2010
Synchronizing Automata on Quasi Eulerian Digraph
In 1964 \v{C}ern\'{y} conjectured that each -state synchronizing automaton
posesses a reset word of length at most . From the other side the best
known upper bound on the reset length (minimum length of reset words) is cubic
in . Thus the main problem here is to prove quadratic (in ) upper bounds.
Since 1964, this problem has been solved for few special classes of \sa. One of
this result is due to Kari \cite{Ka03} for automata with Eulerian digraphs. In
this paper we introduce a new approach to prove quadratic upper bounds and
explain it in terms of Markov chains and Perron-Frobenius theories. Using this
approach we obtain a quadratic upper bound for a generalization of Eulerian
automata.Comment: 8 pages, 1 figur
Evidence of a Solar Origin for Pressure Balance Structures in the High-Latitude Solar Wind
Ulysses observations of the high-latitude solar wind have shown that on time scales of \u3c 1 day, the polar wind is dominated by pressure balance structures (PBSs). Fluctuations of the plasma beta within PBSs appear to be strongly correlated with fluctuations in the helium abundance. The correlation occurs in both the northern and southern hemispheres. In addition, a mechanism is apparently at work in the high-latitude solar wind that dissipates the beta/He correlation over a distance of a few AU. Solar wind composition is established at the base of the corona; thus, the He abundance signature strongly suggests the observed solar wind PBSs are associated with structures low in the solar atmosphere. In particular, high-beta structures appear to originate in locations of enhanced He abundance. We suggest an interpretation of the high-beta portion of PBSs as the solar wind extensions of polar plumes
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
Hypertriglyceridaemia‐induced pancreatitis prompted by acute corticosteroid treatment: caution for clinicians
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/148397/1/imj14228.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/148397/2/imj14228_am.pd
Mixing by polymers: experimental test of decay regime of mixing
By using high molecular weight fluorescent passive tracers with different
diffusion coefficients and by changing the fluid velocity we study dependence
of a characteristic mixing length on the Peclet number, , which controls
the mixing efficiency. The mixing length is found to be related to by a
power law, , and increases faster than
expected for an unbounded chaotic flow. Role of the boundaries in the mixing
length abnormal growth is clarified. The experimental findings are in a good
quantitative agreement with the recent theoretical predictions.Comment: 4 pages,5 figures. accepted for publication in PR
Elastic turbulence in von Karman swirling flow between two disks
We discuss the role of elastic stress in the statistical properties of
elastic turbulence, realized by the flow of a polymer solution between two
disks. The dynamics of the elastic stress are analogous to those of a small
scale fast dynamo in magnetohydrodynamics, and to those of the turbulent
advection of a passive scalar in the Batchelor regime. Both systems are
theoretically studied in literature, and this analogy is exploited to explain
the statistical properties, the flow structure, and the scaling observed
experimentally. Several features of elastic turbulence are confirmed
experimentally and presented in this paper: (i) saturation of the rms of the
vorticity and of velocity gradients in the bulk, leading to the saturation of
the elastic stress; (ii) large rms of the velocity gradients in the boundary
layer, linearly growth with Wi; (iii) skewed PDFs of the injected power, with
exponential tails, which indicate intermittency; PDF of the acceleration
exhibit well-pronounced exponential tails too; (iv) a new length scale, i.e the
thickness of the boundary layer, as measured from the profile of the rms of the
velocity gradient, is found to be relevant and much smaller than the vessel
size; (v) the scaling of the structure functions of the vorticity, velocity
gradients, and injected power is found to be the same as that of a passive
scalar advected by an elastic turbulent velocity field.Comment: submitted to Physics of Fluids; 31 pages, 29 figures (resolution
reduced to screen quality
Understanding and Affecting Student Reasoning About Sound Waves
Student learning of sound waves can be helped through the creation of
group-learning classroom materials whose development and design rely on
explicit investigations into student understanding. We describe reasoning in
terms of sets of resources, i.e. grouped building blocks of thinking that are
commonly used in many different settings. Students in our university physics
classes often used sets of resources that were different from the ones we wish
them to use. By designing curriculum materials that ask students to think about
the physics from a different view, we bring about improvement in student
understanding of sound waves. Our curriculum modifications are specific to our
own classes, but our description of student learning is more generally useful
for teachers. We describe how students can use multiple sets of resources in
their thinking, and raise questions that should be considered by both
instructors and researchers.Comment: 23 pages, 4 figures, 3 tables, 28 references, 7 notes. Accepted for
publication in the International Journal of Science Educatio
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