Collision damping in the pi 3He -> d'N reaction near the threshold

We present a simple quantum mechanical model exploiting the optical potential approach for the description of collision damping in the reaction pi 3He -> d'N near the threshold, which recently has been measured at TRIUMF. The influence of the open d'N -> NNN channel is taken into account. It leads to a suppression factor of about ten in the d' survival probability. Applications of the method to other reactions are outlined.Comment: RevTeX4, 14 pages, 3 Postscript figures, uses epsfig.sty, to appear in Phys.Rev.

Africa's digital future

The main thrust of this book is to examine whether Africa is in a position to benefit from the digital age, given the continent’s many development challenges and slow adoption of digital technologies. While there is substantial literature on the digital economy and the quickening pace of the Fourth Industrial Revolution (4IR), comparatively little research has been conducted on what the digital age means for Africa. This book aims to close this research gap by using various qualitative and quantitative research methodologies to arrive at a cross-section of original findings and perspectives on how Africa can capitalise on the benefits of digital developments, including their potential to create jobs and bring about more inclusive growth. The book’s main contribution is its coverage of a range of topics that will affect Africa’s digital future, including industrialisation, global value chains, transport and logistics, trade facilitation, labour-market dynamics, employment and education. The theme of digital trade forms a backdrop to many of the chapters, along with references to the COVID-19 pandemic. The book acknowledges that although African countries should learn from international best practices, they need to chart their own course according to their own particular circumstances. By adopting a digital mindset, countries should be able to diversify economically and extend their market reach across the continent. Furthermore, while Africa should be looking to the future and determining how digital technologies can become effective tools of sustainable development, the continent has much catching up to do

Africa's digital future

The main thrust of this book is to examine whether Africa is in a position to benefit from the digital age, given the continent’s many development challenges and slow adoption of digital technologies. While there is substantial literature on the digital economy and the quickening pace of the Fourth Industrial Revolution (4IR), comparatively little research has been conducted on what the digital age means for Africa. This book aims to close this research gap by using various qualitative and quantitative research methodologies to arrive at a cross-section of original findings and perspectives on how Africa can capitalise on the benefits of digital developments, including their potential to create jobs and bring about more inclusive growth. The book’s main contribution is its coverage of a range of topics that will affect Africa’s digital future, including industrialisation, global value chains, transport and logistics, trade facilitation, labour-market dynamics, employment and education. The theme of digital trade forms a backdrop to many of the chapters, along with references to the COVID-19 pandemic. The book acknowledges that although African countries should learn from international best practices, they need to chart their own course according to their own particular circumstances. By adopting a digital mindset, countries should be able to diversify economically and extend their market reach across the continent. Furthermore, while Africa should be looking to the future and determining how digital technologies can become effective tools of sustainable development, the continent has much catching up to do

Pion double charge exchange on 4He

The doubly differential cross sections for the $^4$He$(\pi^+,\pi^-) 4p$ reaction were calculated using both a two-nucleon sequential single charge exchange model and an intranuclear cascade code. Final state interactions between the two final protons which were the initial neutrons were included in both methods. At incident pion energies of 240 and 270 MeV the low-energy peak observed experimentally in the energy spectrum of the final pions can be understood only if the contribution of pion production is included. The calculated cross sections are compared with data.Comment: 25 pages, 9 figure

Heisenberg frustrated magnets: a nonperturbative approach

Frustrated magnets are a notorious example where the usual perturbative methods are in conflict. Using a nonperturbative Wilson-like approach, we get a coherent picture of the physics of Heisenberg frustrated magnets everywhere between $d=2$ and $d=4$. We recover all known perturbative results in a single framework and find the transition to be weakly first order in $d=3$. We compute effective exponents in good agreement with numerical and experimental data.Comment: 5 pages, Revtex, technical details available at http://www.lpthe.jussieu.fr/~tissie

A non perturbative approach of the principal chiral model between two and four dimensions

We investigate the principal chiral model between two and four dimensions by means of a non perturbative Wilson-like renormalization group equation. We are thus able to follow the evolution of the effective coupling constants within this whole range of dimensions without having recourse to any kind of small parameter expansion. This allows us to identify its three dimensional critical physics and to solve the long-standing discrepancy between the different perturbative approaches that characterizes the class of models to which the principal chiral model belongs.Comment: 5 pages, 1 figure, Revte

Optimization of the derivative expansion in the nonperturbative renormalization group

We study the optimization of nonperturbative renormalization group equations truncated both in fields and derivatives. On the example of the Ising model in three dimensions, we show that the Principle of Minimal Sensitivity can be unambiguously implemented at order $\partial^2$ of the derivative expansion. This approach allows us to select optimized cut-off functions and to improve the accuracy of the critical exponents $\nu$ and $\eta$. The convergence of the field expansion is also analyzed. We show in particular that its optimization does not coincide with optimization of the accuracy of the critical exponents.Comment: 13 pages, 9 PS figures, published versio

Glacier outflow dissolved organic matter as a window into seasonally changing carbon sources: Leverett Glacier, Greenland

The Greenland Ice Sheet is losing mass at a remarkable rate as a result of climatic warming. This mass loss coincides with the export of dissolved organic matter (DOM) in glacial meltwaters. However, little is known about how the source and composition of exported DOM changes over the melt season, which is key for understanding its fate in downstream ecosystems. Over the 2015 ablation season, we sampled the outflow of Leverett Glacier, a large land‐terminating glacier of the Greenland Ice Sheet. Dissolved organic carbon (DOC) concentrations and DOM fluorescence were analyzed to assess the evolution of DOM sources over the course of the melt season. DOC concentrations and red‐shifted fluorescence were highly associated (R2 > 0.95) and suggest terrestrial inputs from overridden soils dominated DOM early season inputs before progressive dilution with increasing discharge. During the outburst period, supraglacial drainage events disrupted the subglacial drainage system and introduced dominant protein‐like fluorescence signatures not observed in basal flow. These results suggest that subglacial hydrology and changing water sources influence exported DOC concentration and DOM composition, and these sources were differentiated using fluorescence characteristics. Red‐shifted fluorescence components were robust proxies for DOC concentration. Finally, the majority of DOM flux, which occurs during the outburst and postoutburst periods, was characterized by protein‐like fluorescence from supraglacial and potentially subglacial microbial sources. As protein‐like fluorescence is linked to the bioavailability of DOM, the observed changes likely reflect seasonal variations in the impact of glacial inputs on secondary production in downstream ecosystems due to shifting hydrologic regimes

Few-body resonances in light nuclei

We have localized several few-body resonances in light nuclei, using methods which can properly handle two- or three-body resonant states. Among other results, we predict the existence of a three-neutron resonance, small spin-orbit splittings between the low-lying states in He-5 and Li-5, the nonexistence of the soft dipole resonance in He-6, new 1+ states in Li-8 and B-8, and the presence of a nonlinear amplification phenomenon in the 0+_2 state of C-12