3,556 research outputs found
The dynamics of critical Kauffman networks under asynchronous stochastic update
We show that the mean number of attractors in a critical Boolean network
under asynchronous stochastic update grows like a power law and that the mean
size of the attractors increases as a stretched exponential with the system
size. This is in strong contrast to the synchronous case, where the number of
attractors grows faster than any power law.Comment: submitted to PR
Next-to-leading order QCD corrections to one hadron-production in polarized pp collisions at RHIC
We calculate the next-to-leading order QCD corrections to the spin-dependent
cross section for single-inclusive hadron production in hadronic collisions.
This process will be soon studied experimentally at RHIC, providing a tool to
unveil the polarized gluon distribution . We observe a considerably
improvement in the perturbative stability for both unpolarized and polarized
cross sections. The NLO corrections are found to be non-trivial, resulting in a
reduction of the asymmetry.Comment: 8 pages, RevTeX4, 9 figures include
Resonant and Kondo tunneling through molecular magnets
Transport through molecular magnets is studied in the regime of strong
coupling to the leads. We consider a resonant-tunneling model where the
electron spin in a quantum dot or molecule is coupled to an additional local,
anisotropic spin via exchange interaction. The two opposite regimes dominated
by resonant tunneling and by Kondo transport, respectively, are considered. In
the resonant-tunneling regime, the stationary state of the impurity spin is
calculated for arbitrarily strong molecule-lead coupling using a
master-equation approach, which treats the exchange interaction perturbatively.
We find that the characteristic fine structure in the differential conductance
persists even if the hybridization energy exceeds thermal energies. Transport
in the Kondo regime is studied within a diagrammatic approach. We show that
magnetic anisotropy gives rise to a splitting of the Kondo peak at low bias
voltages.Comment: 13 pages, 5 figures, version as publishe
Dynamical multistability in high-finesse micromechanical optical cavities
We analyze the nonlinear dynamics of a high-finesse optical cavity in which
one mirror is mounted on a flexible mechanical element. We find that this
system is governed by an array of dynamical attractors, which arise from
phase-locking between the mechanical oscillations of the mirror and the ringing
of the light intensity in the cavity. We describe an analytical approximation
to map out the diagram of attractors in parameter space, derive the slow
amplitude dynamics of the system, including thermally activated hopping between
different attractors, and suggest a scheme for exploiting the dynamical
multistability in the measurement of small displacements.Comment: 5 pages, 4 figure
Quantum Theory of Cavity-Assisted Sideband Cooling of Mechanical Motion
We present a fully quantum theory describing the cooling of a cantilever
coupled via radiation pressure to an illuminated optical cavity. Applying the
quantum noise approach to the fluctuations of the radiation pressure force, we
derive the opto-mechanical cooling rate and the minimum achievable phonon
number. We find that reaching the quantum limit of arbitrarily small phonon
numbers requires going into the good cavity (resolved phonon sideband) regime
where the cavity linewidth is much smaller than the mechanical frequency and
the corresponding cavity detuning. This is in contrast to the common assumption
that the mechanical frequency and the cavity detuning should be comparable to
the cavity damping.Comment: 5 pages, 2 figure
Persistent holes in a fluid
We observe stable holes in a vertically oscillated 0.5 cm deep aqueous
suspension of cornstarch for accelerations a above 10g. Holes appear only if a
finite perturbation is applied to the layer. Holes are circular and
approximately 0.5 cm wide, and can persist for more than 10^5 cycles. Above a =
17g the rim of the hole becomes unstable producing finger-like protrusions or
hole division. At higher acceleration, the hole delocalizes, growing to cover
the entire surface with erratic undulations. We find similar behavior in an
aqueous suspension of glass microspheres.Comment: 4 pages, 6 figure
Prospects of Open Charm Production at GSI-FAIR and J-PARC
We present a detailed phenomenological study of the prospects of open charm
physics at the future and facilities GSI-FAIR and J-PARC,
respectively. In particular, we concentrate on differential cross sections and
the charge and longitudinal double-spin asymmetries at next-to-leading order
accuracy. Theoretical uncertainties for the proposed observables are estimated
by varying the charm quark mass and the renormalization and factorization
scales.Comment: 11 pages, 13 figure
Fleming's bound for the decay of mixed states
Fleming's inequality is generalized to the decay function of mixed states. We
show that for any symmetric hamiltonian and for any density operator
on a finite dimensional Hilbert space with the orthogonal projection onto
the range of there holds the estimate \Tr(\Pi \rme^{-\rmi ht}\rho
\rme^{\rmi ht}) \geq\cos^{2}((\Delta h)_{\rho}t) for all real with
We show that equality either holds for all
or it does not hold for a single with All the density operators saturating the bound for
all i.e. the mixed intelligent states, are determined.Comment: 12 page
Poynting's theorem and energy conservation in the propagation of light in bounded media
Starting from the Maxwell-Lorentz equations, Poynting's theorem is
reconsidered. The energy flux vector is introduced as S_e=(E x B)/mu_0 instead
of E x H, because only by this choice the energy dissipation can be related to
the balance of the kinetic energy of the matter subsystem. Conservation of the
total energy as the sum of kinetic and electromagnetic energy follows. In our
discussion, media and their microscopic nature are represented exactly by their
susceptibility functions, which do not necessarily have to be known. On this
footing, it can be shown that energy conservation in the propagation of light
through bounded media is ensured by Maxwell's boundary conditions alone, even
for some frequently used approximations. This is demonstrated for approaches
using additional boundary conditions and the dielectric approximation in
detail, the latter of which suspected to violate energy conservation for
decades.Comment: 5 pages, RevTeX4, changes: complete rewrit
Tangential View and Intraoperative Three-Dimensional Fluoroscopy for the Detection of Screw-Misplacements in Volar Plating of Distal Radius Fractures
Background: Volar locking plate fixation has become the gold standard in the treatment of unstable distal radius fractures. Juxta-articular screws should be placed as close as possible to the subchondral zone, in an optimized length to buttress the articular surface and address the contralateral cortical bone. On the other hand, intra-articular screw misplacements will promote osteoarthritis, while the penetration of the contralateral bone surface may result in tendon irritations and ruptures. The intraoperative control of fracture reduction and implant positioning is limited in the common postero-anterior and true lateral two-dimensional (2D)-fluoroscopic views. Therefore, additional 2D-fluoroscopic views in different projections and intraoperative three-dimensional (3D) fluoroscopy were recently reported. Nevertheless, their utility has issued controversies.
Objectives: The following questions should be answered in this study; 1) Are the additional tangential view and the intraoperative 3D fluoroscopy useful in the clinical routine to detect persistent fracture dislocations and screw misplacements, to prevent revision surgery? 2) Which is the most dangerous plate hole for screw misplacement?
Patients and Methods: A total of 48 patients (36 females and 13 males) with 49 unstable distal radius fractures (22 x 23 A; 2 x 23 B, and 25 x 23 C) were treated with a 2.4 mm variable angle LCP Two-Column volar distal radius plate (Synthes GmbH, Oberdorf, Switzerland) during a 10-month period. After final fixation, according to the manufactures' technique guide and control of implant placement in the two common perpendicular 2D-fluoroscopic images (postero-anterior and true lateral), an additional tangential view and intraoperative 3D fluoroscopic scan were performed to control the anatomic fracture reduction and screw placements. Intraoperative revision rates due to screw misplacements (intra-articular or overlength) were evaluated. Additionally, the number of surgeons, time and radiation-exposure, for each step of the operating procedure, were recorded.
Results: In the standard 2D-fluoroscopic views (postero-anterior and true lateral projection), 22 screw misplacements of 232 inserted screws were not detected. Based on the additional tangential view, 12 screws were exchanged, followed by further 10 screws after performing the 3D fluoroscopic scan. The most lateral screw position had the highest risk for screw misplacement (accounting for 45.5% of all exchanged screws). The mean number of images for the tangential view was 3 ± 2.5 images. The mean surgical time was extended by 10.02 ± 3.82 minutes for the 3D fluoroscopic scan. An additional radiation exposure of 4.4 ± 4.5seconds, with a dose area product of 39.2 ± 14.5 cGy/cm2 were necessary for the tangential view and 54.4 ± 20.9 seconds with a dose area product of 2.1 ± 2.2 cGy/cm2, for the 3D fluoroscopic scan.
Conclusions: We recommend the additional 2D-fluoroscopic tangential view for detection of screw misplacements caused by overlength, with penetration on the dorsal cortical surface of the distal radius, predominantly observed for the most lateral screw position. The use of intraoperative 3D fluoroscopy did not become accepted in our clinical routine, due to the technical demanding and time consuming procedure, with a limited image quality so far
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