3,324 research outputs found
Capturing Hiproofs in HOL Light
Hierarchical proof trees (hiproofs for short) add structure to ordinary proof
trees, by allowing portions of trees to be hierarchically nested. The
additional structure can be used to abstract away from details, or to label
particular portions to explain their purpose. In this paper we present two
complementary methods for capturing hiproofs in HOL Light, along with a tool to
produce web-based visualisations. The first method uses tactic recording, by
modifying tactics to record their arguments and construct a hierarchical tree;
this allows a tactic proof script to be modified. The second method uses proof
recording, which extends the HOL Light kernel to record hierachical proof trees
alongside theorems. This method is less invasive, but requires care to manage
the size of the recorded objects. We have implemented both methods, resulting
in two systems: Tactician and HipCam
Stark shift and field ionization of arsenic donors in Si-SOI structures
We develop an efficient back gate for silicon-on-insulator (SOI) devices
operating at cryogenic temperatures, and measure the quadratic hyperfine Stark
shift parameter of arsenic donors in isotopically purified Si-SOI layers
using such structures. The back gate is implemented using MeV ion implantation
through the SOI layer forming a metallic electrode in the handle wafer,
enabling large and uniform electric fields up to 2 V/m to be
applied across the SOI layer. Utilizing this structure we measure the Stark
shift parameters of arsenic donors embedded in the Si SOI layer and find
a contact hyperfine Stark parameter of m/V. We also demonstrate electric-field driven dopant ionization in
the SOI device layer, measured by electron spin resonance.Comment: 5 pages, 3 figure
Semiclassical ionization dynamics of the hydrogen molecular ion in an electric field of arbitrary orientation
Quasi-static models of barrier suppression have played a major role in our
understanding of the ionization of atoms and molecules in strong laser fields.
Despite their success, in the case of diatomic molecules these studies have so
far been restricted to fields aligned with the molecular axis. In this paper we
investigate the locations and heights of the potential barriers in the hydrogen
molecular ion in an electric field of arbitrary orientation. We find that the
barriers undergo bifurcations as the external field strength and direction are
varied. This phenomenon represents an unexpected level of intricacy even on
this most elementary level of the dynamics. We describe the dynamics of
tunnelling ionization through the barriers semiclassically and use our results
to shed new light on the success of a recent theory of molecular tunnelling
ionization as well as earlier theories that restrict the electric field to be
aligned with the molecular axis
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Contributions to twentieth century total column ozone change from halocarbons, tropospheric ozone precursors, and climate change
We investigate ozone changes from preindustrial times
to the present using a chemistry-climate model. The
influence of changes in physical climate, ozone-depleting
substances, N2O, and tropospheric ozone precursors is estimated using equilibrium simulations with these different factors set at either preindustrial or present-day values. When these effects are combined, the entire decrease in total column ozone from preindustrial to present day is very small (–1.8 DU) in the global annual average, though with significant decreases in total column ozone over large parts of the Southern Hemisphere during austral spring and widespread increases in column ozone over the Northern Hemisphere during boreal summer. A significant contribution to the total ozone column change is the increase in lower stratospheric ozone associated with the increase in ozone precursors (5.9 DU). Also noteworthy is the near cancellation of the global average climate change effect on ozone (3.5 DU) by the increase in N2O (–3.9 DU)
Templating porosity in polymethylsilsesquioxane coatings using trimethylsilylated hyperbranched polymers
A series of trimethylsilyl end-functionalized aliphatic hyperbranched polymers has been used to template porosity in polymethylsilsesquioxane films prepared by heat treatment of a spin cast methylsilsesquioxane precursor. By varying the extent of the end-functionalization, closed pore foams with controlled pore sizes and pore contents of up to 40 vol% were obtained by chemically-induced phase separation and thermal degradation of the hyperbranched polymers during the heat treatmen
Direct extraction of the Eliashberg function for electron-phonon coupling: A case study of Be(1010)
We propose a systematic procedure to directly extract the Eliashberg function
for electron-phonon coupling from high-resolution angle-resolved photoemission
data. The procedure is successfully applied to the Be(1010) surface, providing
new insights to electron-phonon coupling at this surface. The method is shown
to be robust against imperfections in experimental data and suitable for wider
applications.Comment: 4 pages, 4 figures. More details concerning the procedure are
include
Confidentiality and public protection: ethical dilemmas in qualitative research with adult male sex offenders
This paper considers the ethical tensions present when engaging in in-depth interviews with convicted sex offenders. Many of the issues described below are similar to those found in other sensitive areas of research. However, confidentiality and public protection are matters that require detailed consideration when the desire to know more about men who have committed serious and harmful offences is set against the possibility of a researcher not disclosing previously unknown sensitive information that relates to the risk of someone being harmed.</p
Cs-Induced Surface State on GaAs(110)
Cesium adsorption on GaAs(110) has been studied by angle-resolved photoemission spectroscopy at room temperature in the submonolayer-coverage regime. We report the observation of a Cs-induced surface state in the vicinity of the surface-Brillouin-zone edge. The possible origin of the state is discussed in relation to recent structural observations. The onset of the Cs-induced surface state can be correlated with the appearance of a second Cs 5p core-level emission feature at ∼0.2 monolayer Cs coverage
Modelling the dynamical evolution of the Bootes dwarf spheroidal galaxy
We investigate a wide range of possible evolutionary histories for the
recently discovered Bootes dwarf spheroidal galaxy, a Milky Way satellite. By
means of N-body simulations we follow the evolution of possible progenitor
galaxies of Bootes for a variety of orbits in the gravitational potential of
the Milky Way. The progenitors considered cover the range from dark-matter-free
star clusters to massive, dark-matter dominated outcomes of cosmological
simulations. For each type of progenitor and orbit we compare the observable
properties of the remnant after 10 Gyr with those of Bootes observed today. Our
study suggests that the progenitor of Bootes must have been, and remains now,
dark matter dominated. In general our models are unable to reproduce the
observed high velocity dispersion in Bootes without dark matter. Our models do
not support time-dependent tidal effects as a mechanism able to inflate
significantly the internal velocity dispersion. As none of our initially
spherical models is able to reproduce the elongation of Bootes, our results
suggest that the progenitor of Bootes may have had some intrinsic flattening.
Although the focus of the present paper is the Bootes dwarf spheroidal, these
models may be of general relevance to understanding the structure, stability
and dark matter content of all dwarf spheroidal galaxies.Comment: 10 pages, 7 figures, accepted by MNRA
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