4,085 research outputs found
Biomechanical evaluation of three surgical scenarios of posterior lumbar interbody fusion by finite element analysis
BACKGROUND: For the treatment of low back pain, the following three scenarios of posterior lumbar interbody fusion (PLIF) were usually used, i.e., PLIF procedure with autogenous iliac bone (PAIB model), PLIF with cages made of PEEK (PCP model) or titanium (Ti) (PCT model) materiel. But the benefits or adverse effects among the three surgical scenarios were still not fully understood. METHOD: Finite element analysis (FEA), as an efficient tool for the analysis of lumbar diseases, was used to establish a three-dimensional nonlinear L1-S1 FE model (intact model) with the ligaments of solid elements. Then it was modified to simulate the three scenarios of PLIF. 10 Nm moments with 400 N preload were applied to the upper L1 vertebral body under the loading conditions of extension, flexion, lateral bending and torsion, respectively. RESULTS: Different mechanical parameters were calculated to evaluate the differences among the three surgical models. The lowest stresses on the bone grafts and the greatest stresses on endplate were found in the PCT model. The PCP model obtained considerable stresses on the bone grafts and less stresses on ligaments. But the changes of stresses on the adjacent discs and endplate were minimal in the PAIB model. CONCLUSIONS: The PCT model was inferior to the other two models. Both the PCP and PAIB models had their own relative merits. The findings provide theoretical basis for the choice of a suitable surgical scenario for different patients
Cooling mechanical resonators to quantum ground state from room temperature
Ground-state cooling of mesoscopic mechanical resonators is a fundamental
requirement for test of quantum theory and for implementation of quantum
information. We analyze the cavity optomechanical cooling limits in the
intermediate coupling regime, where the light-enhanced optomechanical coupling
strength is comparable with the cavity decay rate. It is found that in this
regime the cooling breaks through the limits in both the strong and weak
coupling regimes. The lowest cooling limit is derived analytically at the
optimal conditions of cavity decay rate and coupling strength. In essence,
cooling to the quantum ground state requires , with being the mechanical quality factor and
being the thermal phonon number. Remarkably, ground-state
cooling is achievable starting from room temperature, when mechanical
-frequency product , and both of the
cavity decay rate and the coupling strength exceed the thermal decoherence
rate. Our study provides a general framework for optimizing the backaction
cooling of mesoscopic mechanical resonators
Dependence of the decoherence of polarization states in phase-damping channels on the frequency spectrum envelope of photons
We consider the decoherence of photons suffering in phase-damping channels.
By exploring the evolutions of single-photon polarization states and two-photon
polarization-entangled states, we find that different frequency spectrum
envelopes of photons induce different decoherence processes. A white frequency
spectrum can lead the decoherence to an ideal Markovian process. Some color
frequency spectrums can induce asymptotical decoherence, while, some other
color frequency spectrums can make coherence vanish periodically with variable
revival amplitudes. These behaviors result from the non-Markovian effects on
the decoherence process, which may give rise to a revival of coherence after
complete decoherence.Comment: 7 pages, 4 figures, new results added, replaced by accepted versio
Quantum electrodynamics in a whispering-gallery microcavity coated with a polymer nanolayer
Quasi-transverse-electric and -transverse-magnetic fundamental whispering
gallery modes in a polymer-coated silica microtoroid are theoretically
investigated and demonstrated to possess very high-quality factors. The
existence of a nanometer-thickness layer not only evidently reduces the cavity
mode volume but also draws the maximal electric field's position of the mode to
the outside of the silica toroid, where single quantum dots or nanocrystals are
located. Both effects result in a strongly enhanced coherent interaction
between a single dipole (for example, a single defect center in a diamond
crystal) and the quantized cavity mode. Since the coated microtoroid is highly
feasible and robust in experiments, it may offer an excellent platform to study
strong-coupling cavity quantum electrodynamics, quantum information, and
quantum computation
2,2′-[Octane-1,8-diyldioxybis(nitrilomethylidyne)]diphenol
The complete molecule of the title compound, C22H28N2O4, is generated by a crystallographic inversion centre at the mid-point of the central C—C bond. The two benzene rings are parallel to each other with a perpendicular interplanar spacing of 1.488 (2) Å. Intramolecular O—H⋯N hydrogen bonds generate two six-membered rings with S(6) motifs. In the crystal, weak intermolecular C—H⋯O hydrogen bonds link neighbouring molecules into an infinite three-dimensional network, which is further stabilized by weak C—H⋯π interactions
High-Q exterior whispering gallery modes in a metal-coated microresonator
We propose a kind of plasmonic whispering gallery modes highly localized on
the exterior surface of a metal-coated microresonator. This exterior (EX)
surface mode possesses high quality factors at room temperature, and can be
efficiently excited by a tapered fiber. The EX mode can couple to an interior
(IN) mode and this coupling produces a strong anti-crossing behavior, which not
only allows conversion of IN to EX modes, but also forms a long-lived
anti-symmetric mode. As a potential application, the EX mode could be used for
a biosensor with a sensitivity high up to 500 nm per refraction index unit, a
large figure of merit, and a wide detection range
An experimental study on biased cognitive processing in accidentally injured patients with different posttraumatic growth levels
Background: Various studies have assessed the negative and/or positive changes in the aftermath of traumatic events. Accidental injuries (such as accidents, injuries, etc.), for its high incidence and disability rate, is easy to cause serious psychological problems and hinder the physical and psychological rehabilitation of the patients.Material and Methods: To explore the characteristics of attention bias in accidentally injured patients with different levels of Posttraumatic growth (PTG), total score of PTG was adopted to screen out 15 high-PTG group and low-PTG group respectively among accidentally injured patients. Dot probe task was used with positive, negative and neutral facial expression pictures as experimental materials. An experimental design of 2 (facial expression: positive and negative)×2 (consistency of probe point and facial expression: consistent and inconsistent)×2 (PTG level: high and low) was employed.Results: Patients with low PTG level had attention bias toward the negative emotional stimuli, and difficulty in distraction from the negative emotional pictures. The value of D and DI were both significantly greater than 0 (p<0.05). Patients with high PTG level did not demonstrate significant attention bias toward positive or negative emotional stimuli. The responding time of patients with high PTG level was significantly shorter than that in patients with low PTG level in the incongruent task (p<0.05).Conclusion: There are different characteristics of implicit cognitive processing in patients with different level of PTG, suggesting the necessity of psychological intervention on the accidentally injured patients.Keywords: Accidentally injured patients; Posttraumatic growth; Attention bias; Dot probe tas
Cosmological constraints from the redshift dependence of the Alcock-Paczynski effect: Dynamical dark energy
We perform an anisotropic clustering analysis of 1,133,326 galaxies from the
Sloan Digital Sky Survey (SDSS-III) Baryon Oscillation Spectroscopic Survey
(BOSS) Data Release (DR) 12 covering the redshift range . The
geometrical distortions of the galaxy positions, caused by incorrect
cosmological model assumptions, are captured in the anisotropic two-point
correlation function on scales 6 -- 40 . The redshift evolution
of this anisotropic clustering is used to place constraints on the cosmological
parameters. We improve the methodology of Li et al. 2016, to enable efficient
exploration of high dimensional cosmological parameter spaces, and apply it to
the Chevallier-Polarski-Linder parametrization of dark energy,
. In combination with the CMB, BAO, SNIa and from
Cepheid data, we obtain $\Omega_m = 0.301 \pm 0.008,\ w_0 = -1.042 \pm 0.067,\
w_a = -0.07 \pm 0.29\sim\sim$2. We check the robustness
of the results using realistic mock galaxy catalogues.Comment: 12 pages, 9 figures, accepted to Ap
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