471 research outputs found
Analysis of segmental residual growth after progressive bone lengthening in congenital lower limb deformity
SummaryIntroductionThe issue of prognosis in limb length discrepancy in children affected by congenital abnormality remains a subject of concern. Therapeutic strategy must take length prediction into account, to adapt equalization techniques and the timing of treatment. Initial prognosis, however, may need revising after completion of one or several surgical interventions on the pathologic limb. The aim of this study was to determine the different types of growth response that a bone segment can present after progressive lengthening in case of congenital limb length discrepancy.Materials and methodsA series of 114 bone lengthenings with external fixator, performed in 36 girls and 50 boys with congenital lower limb length discrepancy, was retrospectively analyzed. Bone segment growth rates were measured before lengthening, during the first year after frame removal and finally over long-term follow-up, calculating the ratios of radiological bone length to the number of months between two measurements. Mean follow-up was 4.54±0.2 years.ResultsChanges in short- and long-term growth rate distinguished five patterns of bone behavior after lengthening, ranging from growth acceleration to total inhibition.DiscussionThese five residual growth patterns depended on certain factors causing acceleration or, on the contrary, slowing down of growth: age at the lengthening operation, percentage lengthening, and minimal period between two lengthenings. These criteria help optimize conditions for resumed growth after progressive segmental lengthening, avoiding conditions liable to induce slowing down or inhibition, and providing a planning aid in multi-step lengthening programs.Level of evidenceLevel IV. Retrospective study
Hierarchy of boundary driven phase transitions in multi-species particle systems
Interacting systems with driven particle species on a open chain or
chains which are coupled at the ends to boundary reservoirs with fixed particle
densities are considered. We classify discontinuous and continuous phase
transitions which are driven by adiabatic change of boundary conditions. We
build minimal paths along which any given boundary driven phase transition
(BDPT) is observed and reveal kinetic mechanisms governing these transitions.
Combining minimal paths, we can drive the system from a stationary state with
all positive characteristic speeds to a state with all negative characteristic
speeds, by means of adiabatic changes of the boundary conditions. We show that
along such composite paths one generically encounters discontinuous and
continuous BDPTs with taking values depending on
the path. As model examples we consider solvable exclusion processes with
product measure states and particle species and a non-solvable
two-way traffic model. Our findings are confirmed by numerical integration of
hydrodynamic limit equations and by Monte Carlo simulations. Results extend
straightforwardly to a wide class of driven diffusive systems with several
conserved particle species.Comment: 12 pages, 11 figure
Why spontaneous symmetry breaking disappears in a bridge system with PDE-friendly boundaries
We consider a driven diffusive system with two types of particles, A and B,
coupled at the ends to reservoirs with fixed particle densities. To define
stochastic dynamics that correspond to boundary reservoirs we introduce
projection measures. The stationary state is shown to be approached dynamically
through an infinite reflection of shocks from the boundaries. We argue that
spontaneous symmetry breaking observed in similar systems is due to placing
effective impurities at the boundaries and therefore does not occur in our
system. Monte-Carlo simulations confirm our results.Comment: 24 pages, 7 figure
Steady-state selection in driven diffusive systems with open boundaries
We investigate the stationary states of one-dimensional driven diffusive
systems, coupled to boundary reservoirs with fixed particle densities. We argue
that the generic phase diagram is governed by an extremal principle for the
macroscopic current irrespective of the local dynamics. In particular, we
predict a minimal current phase for systems with local minimum in the
current--density relation. This phase is explained by a dynamical phenomenon,
the branching and coalescence of shocks, Monte-Carlo simulations confirm the
theoretical scenario.Comment: 6 pages, 5 figure
On the Fibonacci universality classes in nonlinear fluctuating hydrodynamics
We present a lattice gas model that without fine tuning of parameters is
expected to exhibit the so far elusive modified Kardar-Parisi-Zhang (KPZ)
universality class. To this end, we review briefly how non-linear fluctuating
hydrodynamics in one dimension predicts that all dynamical universality classes
in its range of applicability belong to an infinite discrete family which we
call Fibonacci family since their dynamical exponents are the Kepler ratios
of neighbouring Fibonacci numbers , including
diffusion (), KPZ (), and the limiting ratio which is the
golden mean . Then we revisit the case of two
conservation laws to which the modified KPZ model belongs. We also derive
criteria on the macroscopic currents to lead to other non-KPZ universality
classes.Comment: 17 page
Symmetry breaking and phase coexistence in a driven diffusive two-channel system
We consider classical hard-core particles moving on two parallel chains in
the same direction. An interaction between the channels is included via the
hopping rates. For a ring, the stationary state has a product form. For the
case of coupling to two reservoirs, it is investigated analytically and
numerically. In addition to the known one-channel phases, two new regions are
found, in particular the one, where the total density is fixed, but the filling
of the individual chains changes back and forth, with a preference for strongly
different densities. The corresponding probability distribution is determined
and shown to have an universal form. The phase diagram and general aspects of
the problem are discussed.Comment: 12 pages, 10 figures, to appear in Phys.Rev.
Scaling of the von Neumann entropy across a finite temperature phase transition
The spectrum of the reduced density matrix and the temperature dependence of
the von Neumann entropy (VNE) are analytically obtained for a system of hard
core bosons on a complete graph which exhibits a phase transition to a
Bose-Einstein condensate at . It is demonstrated that the VNE undergoes
a crossover from purely logarithmic at T=0 to purely linear in block size
behaviour for . For intermediate temperatures, VNE is a sum of two
contributions which are identified as the classical (Gibbs) and the quantum
(due to entanglement) parts of the von Neumann entropy.Comment: 4 pages, 2 figure
Spontaneous Symmetry Breaking in a Non-Conserving Two-Species Driven Model
A two species particle model on an open chain with dynamics which is
non-conserving in the bulk is introduced. The dynamical rules which define the
model obey a symmetry between the two species. The model exhibits a rich
behavior which includes spontaneous symmetry breaking and localized shocks. The
phase diagram in several regions of parameter space is calculated within
mean-field approximation, and compared with Monte-Carlo simulations. In the
limit where fluctuations in the number of particles in the system are taken to
zero, an exact solution is obtained. We present and analyze a physical picture
which serves to explain the different phases of the model
The Fokker-Planck equation, and stationary densities
The most general local Markovian stochastic model is investigated, for which
it is known that the evolution equation is the Fokker-Planck equation. Special
cases are investigated where uncorrelated initial states remain uncorrelated.
Finally, stochastic one-dimensional fields with local interactions are studied
that have kink-solutions.Comment: 10 page
Phase diagram of two-lane driven diffusive systems
We consider a large class of two-lane driven diffusive systems in contact
with reservoirs at their boundaries and develop a stability analysis as a
method to derive the phase diagrams of such systems. We illustrate the method
by deriving phase diagrams for the asymmetric exclusion process coupled to
various second lanes: a diffusive lane; an asymmetric exclusion process with
advection in the same direction as the first lane, and an asymmetric exclusion
process with advection in the opposite direction. The competing currents on the
two lanes naturally lead to a very rich phenomenology and we find a variety of
phase diagrams. It is shown that the stability analysis is equivalent to an
`extremal current principle' for the total current in the two lanes. We also
point to classes of models where both the stability analysis and the extremal
current principle fail
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