The Effect on the Lifetime of an Atom Undergoing a Dipole Transition Due to the Presence of a Resonating Atom

First order perturbation analysis of atom lifetime undergoing dipole transition due to presence of resonating ato

Semi-supervised sequence tagging with bidirectional language models

Pre-trained word embeddings learned from unlabeled text have become a standard component of neural network architectures for NLP tasks. However, in most cases, the recurrent network that operates on word-level representations to produce context sensitive representations is trained on relatively little labeled data. In this paper, we demonstrate a general semi-supervised approach for adding pre- trained context embeddings from bidirectional language models to NLP systems and apply it to sequence labeling tasks. We evaluate our model on two standard datasets for named entity recognition (NER) and chunking, and in both cases achieve state of the art results, surpassing previous systems that use other forms of transfer or joint learning with additional labeled data and task specific gazetteers.Comment: To appear in ACL 201

Explaining Violation Traces with Finite State Natural Language Generation Models

An essential element of any verification technique is that of identifying and communicating to the user, system behaviour which leads to a deviation from the expected behaviour. Such behaviours are typically made available as long traces of system actions which would benefit from a natural language explanation of the trace and especially in the context of business logic level specifications. In this paper we present a natural language generation model which can be used to explain such traces. A key idea is that the explanation language is a CNL that is, formally speaking, regular language susceptible transformations that can be expressed with finite state machinery. At the same time it admits various forms of abstraction and simplification which contribute to the naturalness of explanations that are communicated to the user

Guiding of Rydberg atoms in a high-gradient magnetic guide

We study the guiding of $^{87}$Rb 59D$_{5/2}$ Rydberg atoms in a linear, high-gradient, two-wire magnetic guide. Time delayed microwave ionization and ion detection are used to probe the Rydberg atom motion. We observe guiding of Rydberg atoms over a period of 5 ms following excitation. The decay time of the guided atom signal is about five times that of the initial state. We attribute the lifetime increase to an initial phase of $l$-changing collisions and thermally induced Rydberg-Rydberg transitions. Detailed simulations of Rydberg atom guiding reproduce most experimental observations and offer insight into the internal-state evolution

Life and letters of Robert Louis Stevenson

Thesis (Ed.M.)--Boston University This item was digitized by the Internet Archive

Properties of Bose-Mesons

The Thesis contains an analysis of the properties of the pi-meson. Current meson theory is used in an attempt to distinguish between possible meson types. After a survey of the experimental data involving mesons as real particles, there is a brief summary of the theory involved. An approximate method is proposed for the computation of cross-sections for meson processes involving matrix elements over exact nucleon eigenstates. The validity of this approach, the distorted wave approximation, is considered in detail for spin zero mesons. Comparison is also made with other phenomenological approaches. The distorted wave approximation is used to calculate cross-sections for the production of pi-mesons in nucleon-nucleon collisions under certain simplifying assumptions concerning the nuclear forces. For a final continuous nuclear relative motion, it is found that low energy nucleon states are favoured. This, in the case of a final neutron-proton system, together with a large contribution from transitions to a final bound deuteron, leads to a meson spectrum well peaked at the highest allowed energies in agreement with recent experiments. The total cross-section depends more on the shape and size of the inter-nucleon potential than on the meson type, but the spectrum at a given angle, and, more particularly, the angular distribution, are critically dependent on the parity of the meson produced. A comparison with experiment favours scalar mesons. There is also a consideration of the relatively small cross-section for the production of neutral pi-mesons in the observations of simple collisions. The absorption of pi-mesons by nuclei is then discussed on the assumption that capture takes place from the close shells of the meson-nuclear system. Detailed calculations are presented for the direct capture by heavy nuclei, and for various capture processes in Deuterium. When compared with recent observations, the selection rules for the absorption of mesons in light nuclei favour pseudoscalar mesons. The final problem considered is of a different character, and consists of a field theoretical calculation using Pauli regulators with the Feynman technique. It concerns the decay of heavy neutral bosons to two pi-mesons through an assumed nucleon coupling. Comparison is made with the various V-meson decays reported in cosmic ray photographs. Chapter Six summarises the contemporary position of the relation of meson theory in the light of the calculations presented in this paper, with experiment

Microscopic Theory of Spontaneous Decay in a Dielectric

The local field correction to the spontanous dacay rate of an impurity source atom imbedded in a disordered dielectric is calculated to second order in the dielectric density. The result is found to differ from predictions associated with both "virtual" and "real" cavity models of this decay process. However, if the contributions from two dielectric atoms at the same position are included, the virtual cavity result is reproduced.Comment: 12 Page

Scale-invariant large nonlocality in polycrystalline graphene

The observation of large nonlocal resistances near the Dirac point in graphene has been related to a variety of intrinsic Hall effects, where the spin or valley degrees of freedom are controlled by symmetry breaking mechanisms. Engineering strong spin or valley Hall signals on scalable graphene devices could stimulate further practical developments of spin- and valleytronics. Here we report on scale-invariant nonlocal transport in large-scale chemical vapour deposition graphene under an applied external magnetic field. Contrary to previously reported Zeeman spin Hall effect, our results are explained by field-induced spin-filtered edge states whose sensitivity to grain boundaries manifests in the nonlocal resistance. This phenomenon, related to the emergence of the quantum Hall regime, persists up to the millimeter scale, showing that polycrystalline morphology can be imprinted in nonlocal transport. This suggests that topological Hall effects in large-scale graphene materials are highly sensitive to the underlying structural morphology, limiting practical realizations.Comment: Main paper (14 pages, 5 figures) and Supplementary information (8 pages, 8 figures