16,400 research outputs found
Radical anterior decompression and fusion for cervical spondylotic myelopathy
Sixty-seven patients with cervical spondylotic myelopathy were treated by radical anterior decompression and anterior spinal fusion. Of the 51 patients followed post-operatively for an average of 4.02 years, 34 obtained complete or partial relief, nine were unchanged and two deteriorated. Early complete anterior decompression and spinal fusion led to the most favourable results.published_or_final_versio
Creep and fracture behavior of peak-aged Mg-11Y-5Gd-2Zn-0.5Zr (wt pct)
The tensile-creep and creep-fracture behavior of peak-aged Mg-11Y-5Gd-2Zn-0.5Zr (wt pct) (WGZ1152) was investigated at temperatures between 523 K (250 °C) to 598 K (325 °C) (0.58 to 0.66 T m) and stresses between 30 MPa to 140 MPa. The minimum creep rate of the alloy was almost two orders of magnitude lower than that for WE54-T6 and was similar to that for HZ32-T5. The creep behavior exhibited an extended tertiary creep stage, which was believed to be associated with precipitate coarsening. The creep stress exponent value was 4.5, suggesting that dislocation creep was the rate-controlling mechanism during secondary creep. At T = 573 K (300 °C), basal slip was the dominant deformation mode. The activation energy for creep (Q avg = 221 ± 20 kJ/mol) was higher than that for self-diffusion in magnesium and was believed to be associated with the presence of second-phase particles as well as the activation of nonbasal slip and cross slip. This finding was consistent with the slip-trace analysis and surface deformation observations, which revealed that the nonbasal slip was active. The minimum creep rate and time-to-fracture followed the original and modified Monkman-Grant relationships. The microcracks and cavities nucleated preferentially at grain boundaries and at the interface between the matrix phase and the second phase. In-situ creep experiments highlighted the intergranular cracking evolution
Creep and fracture behavior of peak-aged Mg-11Y-5Gd-2Zn-0.5Zr (wt pct)
The tensile-creep and creep-fracture behavior of peak-aged Mg-11Y-5Gd-2Zn-0.5Zr (wt pct) (WGZ1152) was investigated at temperatures between 523 K (250 °C) to 598 K (325 °C) (0.58 to 0.66 T m) and stresses between 30 MPa to 140 MPa. The minimum creep rate of the alloy was almost two orders of magnitude lower than that for WE54-T6 and was similar to that for HZ32-T5. The creep behavior exhibited an extended tertiary creep stage, which was believed to be associated with precipitate coarsening. The creep stress exponent value was 4.5, suggesting that dislocation creep was the rate-controlling mechanism during secondary creep. At T = 573 K (300 °C), basal slip was the dominant deformation mode. The activation energy for creep (Q avg = 221 ± 20 kJ/mol) was higher than that for self-diffusion in magnesium and was believed to be associated with the presence of second-phase particles as well as the activation of nonbasal slip and cross slip. This finding was consistent with the slip-trace analysis and surface deformation observations, which revealed that the nonbasal slip was active. The minimum creep rate and time-to-fracture followed the original and modified Monkman-Grant relationships. The microcracks and cavities nucleated preferentially at grain boundaries and at the interface between the matrix phase and the second phase. In-situ creep experiments highlighted the intergranular cracking evolution
Incentivizing High Quality Crowdwork
We study the causal effects of financial incentives on the quality of
crowdwork. We focus on performance-based payments (PBPs), bonus payments
awarded to workers for producing high quality work. We design and run
randomized behavioral experiments on the popular crowdsourcing platform Amazon
Mechanical Turk with the goal of understanding when, where, and why PBPs help,
identifying properties of the payment, payment structure, and the task itself
that make them most effective. We provide examples of tasks for which PBPs do
improve quality. For such tasks, the effectiveness of PBPs is not too sensitive
to the threshold for quality required to receive the bonus, while the magnitude
of the bonus must be large enough to make the reward salient. We also present
examples of tasks for which PBPs do not improve quality. Our results suggest
that for PBPs to improve quality, the task must be effort-responsive: the task
must allow workers to produce higher quality work by exerting more effort. We
also give a simple method to determine if a task is effort-responsive a priori.
Furthermore, our experiments suggest that all payments on Mechanical Turk are,
to some degree, implicitly performance-based in that workers believe their work
may be rejected if their performance is sufficiently poor. Finally, we propose
a new model of worker behavior that extends the standard principal-agent model
from economics to include a worker's subjective beliefs about his likelihood of
being paid, and show that the predictions of this model are in line with our
experimental findings. This model may be useful as a foundation for theoretical
studies of incentives in crowdsourcing markets.Comment: This is a preprint of an Article accepted for publication in WWW
\c{opyright} 2015 International World Wide Web Conference Committe
Observation of giant positive magnetoresistance in a Cooper pair insulator.
Ultrathin amorphous Bi films, patterned with a nanohoneycomb array of holes, can exhibit an insulating phase with transport dominated by the incoherent motion of Cooper pairs (CP) of electrons between localized states. Here, we show that the magnetoresistance (MR) of this Cooper pair insulator (CPI) phase is positive and grows exponentially with decreasing temperature T, for T well below the pair formation temperature. It peaks at a field estimated to be sufficient to break the pairs and then decreases monotonically into a regime in which the film resistance assumes the T dependence appropriate for weakly localized single electron transport. We discuss how these results support proposals that the large MR peaks in other unpatterned, ultrathin film systems disclose a CPI phase and provide new insight into the CP localization
Molybdenum Evidence for Inherited Planetary Scale Isotope Heterogeneity of the Protosolar Nebula
Isotope anomalies provide important information about early solar system
evolution. Here we report molybdenum isotope abundances determined in samples
of various meteorite classes. There is no fractionation of molybdenum isotopes
in our sample set within 0.1 permil and no contribution from the extinct
radionuclide 97Tc at mass 97 (97Tc/92Mo<3E-6). Instead, we observe clear
anomalies in bulk iron meteorites, mesosiderites, pallasites, and chondrites
characterized by a coupled excess in p- and r- or a mirror deficit in s-process
nuclides (Mo-HL). This large scale isotope heterogeneity of the solar system
observed for molybdenum must have been inherited from the interstellar
environment where the sun was born, illustrating the concept of ``cosmic
chemical memory''. The presence of molybdenum anomalies is used to discuss the
filiation between planetesimals.Comment: 7 pages, 2 figures, 1 table, accepted in Ap
Lanthanum distribution and dielectric properties of intergrowth Bi₅ˍₓLaₓTiNbWO₁₅ ferroelectrics
Bi₅ˍₓLaₓTiNbWO₁₅ (x=0–1.50)ceramics prepared by conventional solid-state reaction were studied using x-ray diffraction(XRD),dielectric spectroscopy and Raman scattering techniques. The XRD analysis implied that single-phase intergrowth bismuth layered perovskite structure was obtained for all the samples and when x=0.75, the Bi³⁺ in (Bi₂O₂)²⁺ layer begins to be substituted by La³⁺. The dielectric spectra showed that, when Bi³⁺ in (Bi₂O₂)²⁺ is substituted, the Curie temperature becomes diffusive and the dielectricpermittivity at room temperature is increased in a wide frequency range. Especially when x=1.50, the dielectricpermittivity reaches its maximum of 270, nearly two times larger than that of the La3+ undoped sample. The Raman scattering experiments evidenced further that Bi³⁺ in (Bi₂O₂)²⁺ is substituted when x⩾0.75 and revealed the orthorhombic distortion of the octahedra is responsible for the increase of the dielectricpermittivity at x⩾1.25.This work was supported by the Ministry of Science and
Technology of China through 973-Project under Grant No.
2002CB613307
Efficient Phase-Encoding Quantum Key Generation with Narrow-Band Single Photons
We propose an efficient phase-encoding quantum secret key generation scheme
with heralded narrow-band single photons. The key information is carried by the
phase modulation directly on the single-photon temporal waveform without using
any passive beam splitters or optical switches. We show that, when the
technique is applied to the conventional fiber-based phase-encoding BB84 and
differential phase shift (DPS) quantum key distribution schemes, the key
generation efficiencies can be improved by a factor of 2 and 3, respectively.
For N(>3)-period DPS systems, the key generation efficiency can be improved by
a factor of N. The technique is suitable for quantum memory-based long-distance
fiber communication system.Comment: 5 pages, 5 figure
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