1,162 research outputs found
Shear bands and cracking of metallic glass plates in bending
The thickness dependence of yielding and fracture of metallic glass plates subjected to bending is considered in terms of the shear band processes responsible for these properties. We argue that the shear band spacing (and length) scales with the thickness of the plate because of strain relaxation in the vicinity of the shear band at the surface. This is consistent with recent measurements of shear band spacing versus sample size. We also argue that the shear displacements in the shear band scale with the shear band length and plate thickness, thus causing cracks to be initiated in thicker plates at smaller bending strains. This leads to fracture bending strains that decrease markedly with increasing plate thickness, consistent with recent experiments. These results suggest that amorphous metals in the form of foams might have superior ductility and toughness
Nuclear Ground-State Masses and Deformations
We tabulate the atomic mass excesses and nuclear ground-state deformations of
8979 nuclei ranging from O to . The calculations are based on the
finite-range droplet macroscopic model and the folded-Yukawa single-particle
microscopic model. Relative to our 1981 mass table the current results are
obtained with an improved macroscopic model, an improved pairing model with a
new form for the effective-interaction pairing gap, and minimization of the
ground-state energy with respect to additional shape degrees of freedom. The
values of only 9 constants are determined directly from a least-squares
adjustment to the ground-state masses of 1654 nuclei ranging from O to
106 and to 28 fission-barrier heights. The error of the mass model is
0.669~MeV for the entire region of nuclei considered, but is only 0.448~MeV for
the region above .Comment: 50 pages plus 20 PostScript figures and 160-page table obtainable by
anonymous ftp from t2.lanl.gov in directory masses, LA-UR-93-308
BREXIT: Psychometric Profiling the Political Salubrious Through Machine Learning: Predicting personality traits of Boris Johnson through Twitter political text
Whilst the CIA have been using psychometric profiling for decades, Cambridge Analytica showed that people\u27s psychological characteristics can be accurately predicted from their digital footprints, such as their Facebook or Twitter accounts. To exploit this form of psychological assessment from digital footprints, we propose machine learning methods for assessing political personality from Twitter. We have extracted the tweet content of Prime Minster Boris Johnsonâs Twitter account and built three predictive personality models based on his Twitter political content. We use a Multi-Layer Perceptron Neural network, a Naive Bayes multinomial model and a Support Machine Vector model to predict the OCEAN model which consists of the Big Five personality factors from a sample of 3355 political tweets. The approach vectorizes political tweets, then it learns word vector representations as embeddings from spaCy that are then used to feed a supervised learner classifier. We demonstrate the effectiveness of the approach by measuring the quality of the predictions for each trait per model from a classification algorithm. Our findings show that all three models compute the personality trait âOpennessâ with the Support Machine Vector model achieving the highest accuracy. âExtraversionâ achieved the second highest accuracy personality score by the Multi-Layer Perceptron neural network and Support Machine Vector model
Final Report: Buffalo National River Ecosystems
The objective of this study was to sample the Buffalo River on a seasonal basis for a year, in order to determine whether any potential water quality problems existed
Statistical Model of Heavy-Ion Fusion-Fission Reactions
Cross-section and neutron-emission data from heavy-ion fusion-fission
reactions are consistent with the fission of fully equilibrated systems with
fission lifetime estimates obtained via a Kramers-modified statistical model
which takes into account the collective motion of the system about the ground
state, the temperature dependence of the location and height of fission
transition points, and the orientation degree of freedom. If the standard
techniques for calculating fission lifetimes are used, then the calculated
excitation-energy dependence of fission lifetimes is incorrect. We see no
evidence to suggest that the nuclear viscosity has a temperature dependence.
The strong increase in the nuclear viscosity above a temperature of
approximately 1.3 MeV deduced by others is an artifact generated by an
inadequate fission model.Comment: Full paper submitted to PRC to accompany our recently published Phys.
Rev. Lett. 101, 032702 (2008
Memory effects on descent from nuclear fission barrier
Non-Markovian transport equations for nuclear large amplitude motion are
derived from the collisional kinetic equation. The memory effects are caused by
the Fermi surface distortions and depend on the relaxation time. It is shown
that the nuclear collective motion and the nuclear fission are influenced
strongly by the memory effects at the relaxation time . In particular, the descent of the nucleus from the fission
barrier is accompanied by characteristic shape oscillations. The eigenfrequency
and the damping of the shape oscillations depend on the contribution of the
memory integral in the equations of motion. The shape oscillations disappear at
the short relaxation time regime at , which corresponds to the
usual Markovian motion in the presence of friction forces. We show that the
elastic forces produced by the memory integral lead to a significant delay for
the descent of the nucleus from the barrier. Numerical calculations for the
nucleus U shows that due to the memory effect the saddle-to-scission
time grows by a factor of about 3 with respect to the corresponding
saddle-to-scission time obtained in liquid drop model calculations with
friction forces.Comment: 22 pages, 8 figures, submitted to Phys. Rev.
Fission studies with 140 MeV -Particles
Binary fission induced by 140 MeV -particles has been measured for
Ag, La, Ho and Au targets. The measured
quantities are the total kinetic energies, fragment masses, and fission cross
sections. The results are compared with other data and systematics. A minimum
of the fission probability in the vicinity is observed.Comment: 4 figures, 2 table
Characterization of Landau-Zener Transitions in Systems with Complex Spectra
This paper is concerned with the study of one-body dissipation effects in
idealized models resembling a nucleus. In particular, we study the quantum
mechanics of a free particle that collides elastically with the slowly moving
walls of a Bunimovich stadium billiard. Our results are twofold. First, we
develop a method to solve in a simple way the quantum mechanical evolution of
planar billiards with moving walls. The formalism is based on the {\it scaling
method} \cite{ver} which enables the resolution of the problem in terms of
quantities defined over the boundary of the billiard. The second result is
related to the quantum aspects of dissipation in systems with complex spectra.
We conclude that in a slowly varying evolution the energy is transferred from
the boundary to the particle through LandauZener transitions.Comment: 24 pages (including 7 postcript figures), Revtex. Submitted to PR
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