Have transport costs contributed to the relative decline of sub-Saharan African exports? Some preliminary empirical evidence

From the mid-1950s to 1990, sub-Saharan Africa's share of global exports fell from 3.1 to under 1.2 percent, a decline that implies associated export earning losses of about $65 billion annually. Previous studies show that foreign trade barriers do not account for this poor performance. Indeed, African exports enjoy OECD tariff preferences. In the sub-Saharan African countries, too high a proportion of foreign exchange earnings is paying for Africa's high export transport costs. The authors demonstrate that relatively high transportation costs - especially for processed products - often place African exporters at a serious competitive disadvantage. African countries must use a far larger share of their foreign exchange earnings to pay for international transport services than other developing countries do - and the relative importance of those payments has been increasing. Why are Africa's transport costs so high? Ill-advised policies on the part of some African governments seem to have played a role, as their cargo reservation policies produced high"rents"for lines that have been shielded from the effects of competition. The failure to maintain or improve port and transport infrastructure has also played a role.Rural Roads&Transport,Economic Theory&Research,Transport and Trade Logistics,Common Carriers Industry,Environmental Economics&Policies,Transport and Trade Logistics,Common Carriers Industry,TF054105-DONOR FUNDED OPERATION ADMINISTRATION FEE INCOME AND EXPENSE ACCOUNT,Environmental Economics&Policies,Economic Theory&Research

Maximal 2-rainbow domination number of a graph

AbstractA 2-rainbow dominating function (2RDF) of a graph G is a function f from the vertex set V(G) to the set of all subsets of the set {1,2} such that for any vertex v∈V(G) with f(v)=0̸ the condition ⋃u∈N(v)f(u)={1,2} is fulfilled, where N(v) is the open neighborhood of v. A maximal 2-rainbow dominating function on a graph G is a 2-rainbow dominating function f such that the set {w∈V(G)|f(w)=0̸} is not a dominating set of G. The weight of a maximal 2RDF f is the value ω(f)=∑v∈V|f(v)|. The maximal 2-rainbow domination number of a graph G, denoted by γmr(G), is the minimum weight of a maximal 2RDF of G. In this paper we initiate the study of maximal 2-rainbow domination number in graphs. We first show that the decision problem is NP-complete even when restricted to bipartite or chordal graphs, and then, we present some sharp bounds for γmr(G). In addition, we determine the maximal rainbow domination number of some graphs

Thin Circular Diamond Membrane with Embedded Nitrogen-Vacancy Centers for Hybrid Spin-Mechanical Quantum Systems

Coupling mechanical degrees of freedom to single well-controlled quantum systems has become subject to intense research recently. Here, we report on the design, fabrication, and characterization of a diamond architecture consisting of a high-quality thin circular diamond membrane with embedded near-surface nitrogen-vacancy centers (NVCs). To demonstrate this architecture, we employ the NVCs by means of their optical and spin interfaces as nanosensors of the motion of the membrane under static pressure and in-resonance vibration. We also monitor the static residual stress within the membrane using the same method. Driving the membrane at its fundamental resonance mode, we observe coupling of this vibrational mode to the spin of the NVCs. Our realization of this architecture can manifest the applications of diamond structures in 3D piezometry such as mechanobiology and vibrometry, as well as mechanically mediated spin-spin coupling in quantum-information science

Association between duration of symptoms and severity of disease at first presentation to paediatric rheumatology: results from the Childhood Arthritis Prospective Study

Objectives. To study the association between disease severity at first presentation to paediatric rheumatology (PRh) and length of time since symptom onset in children recruited to the Childhood Arthritis Prospective Study

An actionable guide to creating Educational Escape Rooms: handbook

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Stretchable Dual-Capacitor Multi-Sensor for Touch-Curvature-Pressure-Strain Sensing

We introduce a new type of multi-functional capacitive sensor that can sense several different external stimuli. It is fabricated only with polydimethylsiloxane (PDMS) films and silver nanowire electrodes by using selective oxygen plasma treatment method without photolithography and etching processes. Differently from the conventional single-capacitor multi-functional sensors, our new multifunctional sensor is composed of two vertically-stacked capacitors (dual-capacitor). The unique dual-capacitor structure can detect the type and strength of external stimuli including curvature, pressure, strain, and touch with clear distinction, and it can also detect the surface-normal directionality of curvature, pressure, and touch. Meanwhile, the conventional single-capacitor sensor has ambiguity in distinguishing curvature and pressure and it can detect only the strength of external stimulus. The type, directionality, and strength of external stimulus can be determined based on the relative capacitance changes of the two stacked capacitors. Additionally, the logical flow reflected on a tree structure with its branches reaching the direction and strength of the corresponding external stimulus unambiguously is devised. This logical flow can be readily implemented in the sensor driving circuit if the dual-capacitor sensor is commercialized actually in the future

Views and Experiences of Sex, Sexuality and Relationships Following Spinal Cord Injury: A Systematic Review and Narrative Synthesis of the Qualitative Literature

Research examining the effects of spinal cord injury on sexuality has largely focused on physiological functioning and quantification of dysfunction following injury. This paper reports a systematic review of qualitative research that focused on the views and experiences of people with spinal cord injury on sex and relationships. The review addressed the following research question: What are the views and experiences of people with spinal cord injury of sex, sexuality and relationships following injury? Five databases were relevant and employed in the review: CINAHL (1989-2016 only), PsychInfo, PubMed, Scopus and Web of Science, for research published between 1 January 1980 and 30 November 2019. After removing duplicates, 257 records remained and were screened using a two-stage approach to inclusion and quality appraisal. Following screening, 27 met the criteria for inclusion and are reported in the paper. The review includes studies from fifteen countries across five continents. Two main approaches to data analysis summary and thematic synthesis were undertaken to analyze the qualitative data reported in the papers. The analysis revealed four main themes: sexual identity; significant and generalized others, sexual embodiment; and; sexual rehabilitation and education