114,391 research outputs found
Dynamic delamination crack propagation in a graphite/epoxy laminate
Dynamic delamination crack propagation in a (90/0) 5s Graphite/Epoxy laminate with an embedded interfacial crack was investigated experimentally using high speed photography. The dynamic motion was produced by impacting the beamlike laminate specimen with a silicon rubber ball. The threshold impact velocities required to initiate dynamic crack propagation in laminates with varying initial crack positions were determined. The crack propagation speeds were estimated from the photographs. Results show that the through the thickness position of the embedded crack can significantly affect the dominant mechanism and the threshold impact velocity for the onset of crack movement. If the initial delamination is placed near the top of bottom surface of the laminate, local buckling of the delaminated plies may cause instability of the crack. If the initial delamination lies on the midplane, local buckling does not occur and the initiation of crack propagation appears to be dominated by Mode II fracture. The crack propagation and arrest observed was seen to be affected by wave motion within the delamination region
Green's function method for single-particle resonant states in relativistic mean field theory
Relativistic mean field theory is formulated with the Green's function method
in coordinate space to investigate the single-particle bound states and
resonant states on the same footing. Taking the density of states for free
particle as a reference, the energies and widths of single-particle resonant
states are extracted from the density of states without any ambiguity. As an
example, the energies and widths for single-neutron resonant states in
Sn are compared with those obtained by the scattering phase-shift
method, the analytic continuation in the coupling constant approach, the real
stabilization method and the complex scaling method. Excellent agreements are
found for the energies and widths of single-neutron resonant states.Comment: 20 pages, 7 figure
Tunable subpicosecond electron bunch train generation using a transverse-to-longitudinal phase space exchange technique
We report on the experimental generation of a train of subpicosecond electron
bunches. The bunch train generation is accomplished using a beamline capable of
exchanging the coordinates between the horizontal and longitudinal degrees of
freedom. An initial beam consisting of a set of horizontally-separated beamlets
is converted into a train of bunches temporally separated with tunable bunch
duration and separation. The experiment reported in this Letter unambiguously
demonstrates the conversion process and its versatility.Comment: 4 pages, 5 figures, 1 table; accepted for publication in PR
Authorship Attribution Using a Neural Network Language Model
In practice, training language models for individual authors is often
expensive because of limited data resources. In such cases, Neural Network
Language Models (NNLMs), generally outperform the traditional non-parametric
N-gram models. Here we investigate the performance of a feed-forward NNLM on an
authorship attribution problem, with moderate author set size and relatively
limited data. We also consider how the text topics impact performance. Compared
with a well-constructed N-gram baseline method with Kneser-Ney smoothing, the
proposed method achieves nearly 2:5% reduction in perplexity and increases
author classification accuracy by 3:43% on average, given as few as 5 test
sentences. The performance is very competitive with the state of the art in
terms of accuracy and demand on test data. The source code, preprocessed
datasets, a detailed description of the methodology and results are available
at https://github.com/zge/authorship-attribution.Comment: Proceedings of the 30th AAAI Conference on Artificial Intelligence
(AAAI'16
Ground-state phases of rung-alternated spin-1/2 Heisenberg ladder
The ground-state phase diagram of Heisenberg spin-1/2 system on a two-leg
ladder with rung alternation is studied by combining analytical approaches with
numerical simulations. For the case of ferromagnetic leg exchanges a unique
ferrimagnetic ground state emerges, whereas for the case of antiferromagnetic
leg exchanges several different ground states are stabilized depending on the
ratio between exchanges along legs and rungs. For the more general case of a
honeycomb-ladder model for the case of ferromagnetic leg exchanges besides
usual rung-singlet and saturated ferromagnetic states we obtain a ferrimagnetic
Luttinger liquid phase with both linear and quadratic low energy dispersions
and ground state magnetization continuously changing with system parameters.
For the case of antiferromagnetic exchanges along legs, different dimerized
states including states with additional topological order are suggested to be
realized
Formation and Acceleration of Uniformly-Filled Ellipsoidal Electron Bunches Obtained via Space-Charge-Driven Expansion from a Cesium-Telluride Photocathode
We report the experimental generation, acceleration and characterization of a
uniformly-filled electron bunch obtained via space-charge-driven expansion
(often referred to as "blow-out regime") in an L-band (1.3-GHz) radiofrequency
photoinjector. The beam is photoemitted from a Cesium-Telluride semiconductor
photocathode using a short ( fs) ultraviolet laser pulse. The produced
electron bunches are characterized with conventional diagnostics and the
signatures of their ellipsoidal character is observed. We especially
demonstrate the production of ellipsoidal bunches with charges up to
nC corresponding to a -fold increase compared to previous experiments
with metallic photocathodes.Comment: 9, pages, 13 figure
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