State-Selective High-Energy Excitation of Nuclei by Resonant Positron Annihilation

In the annihilation of a positron with a bound atomic electron, the virtual gamma photon created may excite the atomic nucleus. We put forward this effect as a spectroscopic tool for an energy-selective excitation of nuclear transitions. This scheme can efficiently populate nuclear levels of arbitrary multipolarities in the MeV regime, including monopole transitions and giant resonances. In certain cases, it may have a higher cross sections than the conventionally used Coulomb excitation

Two-loop QED corrections with closed fermion loops for the bound-electron g factor

Two-loop QED corrections with closed fermion loops are calculated for the 1s bound-electron g factor. Calculations are performed to all orders in the nuclear binding strength parameter Z\alpha (where Z is the nuclear charge and \alpha is the fine structure constant) except for the closed fermion loop, which is treated within the free-loop (Uehling) approximation in some cases. Comparison with previous Z\alpha-expansion calculations is made and the higher-order remainder of order \alpha^2(Z\alpha)^5 and higher is separated out from the numerical results

Analysis of standing vertical jumps using a force platform

A force platform analysis of vertical jumping provides an engaging demonstration of the kinematics and dynamics of one-dimensional motion. The height of the jump may be calculated (1) from the flight time of the jump, (2) by applying the impulse–momentum theorem to the force–time curve, and (3) by applying the work–energy theorem to the force-displacement curve

The effects of climate change and variation in New Zealand: An assessment using the CLIMPACTS system

Along with a need to better understand the climate and biophysical systems of New Zealand, the need to develop an improved capacity for evaluating possible changes in climate and their effects on the New Zealand environment has been recognised. Since the middle of 1993 the CLIMPACTS programme, has been focused on the development of such a capacity, in the first instance for the agricultural sector. the goals of this present assessment are: 1. To present current knowledge on likely scenarios of climate change and associated uncertainties in New Zealand; 2. To present current knowledge, based on quantitative analyses using a consistent set of scenarios, on the likely effects of climate change on a range of agricultural and horticultural crops of economic importance; 3. To demonstrate, by way of this report and the associated technical report, the capacity that has been developed for ongoing assessments of this kind in New Zealand. This report has been prepared for both the science and policy communities in New Zealand. There are two main components: 1. The detailed findings of the assessment, presented in a series of chapters; 2. An annex, which contains technical details on models used in the assessment

Mixing and merging for spoken document retrieval

This paper describes a number of experiments that explo- red the issues surrounding the retrieval of spoken documents. Two such issues were examined. First, attempting to find the best use of speech recogniser output to produce the highest retrieval effectiveness. Second, investigating the potential problems of retrieving from a so-called "mi- xed collection", i.e. one that contains documents from both a speech recognition system (producing many errors) and from hand transcription (producing presumably near perfect documents). The result of the first part of the work found that merging the transcripts of multiple recognisers showed most promise. The investigation in the second part showed how the term weighting scheme used in a retrieval system was important in determining whether the system was affected detrimentally when retrieving from a mixed collection

Nuclear-size self-energy and vacuum-polarization corrections to the bound-electron g factor

The finite nuclear-size effect on the leading bound-electron g factor and the one-loop QED corrections to the bound-electron g factor is investigated for the ground state of hydrogen-like ions. The calculation is performed to all orders in the nuclear binding strength parameter Z\alpha\ (where Z is the nuclear charge and \alpha\ is the fine structure constant) and for the Fermi model of the nuclear charge distribution. In the result, theoretical predictions for the isotope shift of the 1s bound-electron g factor are obtained, which can be used for the determination of the difference of nuclear charge radii from experimental values of the bound-electron g factors for different isotopes

QED calculation of the nuclear magnetic shielding for hydrogen-like ions

We report an ab initio calculation of the shielding of the nuclear magnetic moment by the bound electron in hydrogen-like ions. This investigation takes into account several effects that have not been calculated before (electron self-energy, vacuum polarization, nuclear magnetization distribution), thus bringing the theory to the point where further progress is impeded by the uncertainty due to nuclear-structure effects. The QED corrections are calculated to all orders in the nuclear binding strength parameter and, independently, to the leading order in the expansion in this parameter. The results obtained lay the ground for the high-precision determination of nuclear magnetic dipole moments from measurements of the g-factor of hydrogen-like ions

QED theory of the nuclear magnetic shielding in hydrogen-like ions

The shielding of the nuclear magnetic moment by the bound electron in hydrogen-like ions is calculated ab initio with inclusion of relativistic, nuclear, and quantum electrodynamics (QED) effects. The QED correction is evaluated to all orders in the nuclear binding strength parameter and, independently, to the first order in the expansion in this parameter. The results obtained lay the basis for the high-precision determination of nuclear magnetic dipole moments from measurements of the g-factor of hydrogen-like ions.Comment: 4 pages, 2 tables, 2 figure

CO2 reduction with protons and electrons at a boron-based reaction center.

Borohydrides are widely used reducing agents in chemical synthesis and have emerging energy applications as hydrogen storage materials and reagents for the reduction of CO2. Unfortunately, the high energy cost associated with the multistep preparation of borohydrides starting from alkali metals precludes large scale implementation of these latter uses. One potential solution to this issue is the direct synthesis of borohydrides from the protonation of reduced boron compounds. We herein report reactions of the redox series [Au(B2P2)] n (n = +1, 0, -1) (B2P2, 9,10-bis(2-(diisopropylphosphino)phenyl)-9,10-dihydroboranthrene) and their conversion into corresponding mono- and diborohydride complexes. Crucially, the monoborohydride can be accessed via protonation of [Au(B2P2)]-, a masked borane dianion equivalent accessible at relatively mild potentials (-2.05 V vs. Fc/Fc+). This species reduces CO2 to produce the corresponding formate complex. Cleavage of the formate complex can be achieved by reduction (ca. -1.7 V vs. Fc/Fc+) or by the addition of electrophiles including H+. Additionally, direct reaction of [Au(B2P2)]- with CO2 results in reductive disproportion to release CO and generate a carbonate complex. Together, these reactions constitute a synthetic cycle for CO2 reduction at a boron-based reaction center that proceeds through a B-H unit generated via protonation of a reduced borane with weak organic acids