Stable propagation of pulsed beams in Kerr focusing media with modulated dispersion

We propose the modulation of dispersion to prevent collapse of planar pulsed beams which propagate in Kerr-type self-focusing optical media. As a result, we find a new type of two-dimensional spatio-temporal solitons stabilized by dispersion management. We have studied the existence and properties of these solitary waves both analytically and numerically. We show that the adequate choice of the modulation parameters optimizes the stabilization of the pulse.Comment: 3 pages, 3 figures, submitted to Optics Letter

Prosperity prospects in contested forest areas: evidence from community forestry development in Guatemala and Nicaragua

Tropentag, September 18-21, 2016, Vienna, Austria “Solidarity in a competing world — fair use of resources” Prosperity Prospects in Contested Forest Areas: Evidence from Community Forestry Development in Guatemala and Nicaragua Dietmar Stoian 1 , Aldo Rodas 2 , Jessenia Arguello 3 1 Bioversity International, Healthy Diets from Sustainable Food Systems Initiative, France 2 Ministry of Agriculture and Livestock, Guatemala, Natural Resources and Agrotourism, 3 Independent Consultant, Abstract Community forestry is carried out under diverse institutional, environmental, and socio-economic conditions. Local communities may have de jure rights to forest resources, but de facto protection is often weak. This study focuses on 25-year community concessions in the Maya Biosphere Reserve (MBR) in Guatemala and indigenous territories in the North Caribbean Coast Autonomous Region (RACCN), Nicaragua. In both cases, communities are struggling to enforce their rights as powerful external groups seek to expand cattle ranching, cash crops, tourism, and oil exploration. We found evidence that community forestry can generate significant socio-economic benefits that, along with contributions to forest conservation, substantiate the communities’ claim for strengthened and extended community forest stewardship. We selected six community forest enterprises (CFEs) along a business development gradient and assessed their context, economic viability, and livelihood benefits among randomly selected CFE members (n=180). Adopting an asset lens, we determined human, social, natural, physical and financial capital endowments at household and enterprise levels. Enterprise assets varied widely, both within and across countries. CFEs were well endowed with natural capital (7,000–54,000 ha of broadleaf forests) but highly dependent on precious woods, such as mahogany ( Swietenia macropylla ) or andiroba ( Carapa guianensis ). Human capital was sufficiently developed for managing forests, but less so for processing wood and doing business. Social capital has been built in Guatemala through internal organisation, bringing CFEs under the umbrella of a regional association, and developing relationships with buyers. In Nicaragua, however, building of social capital has been insufficient for inducing a self-sustaining process of CFE development. Physical capital for logging and wood processing was moderate but, in Guatemala, conditions facilitate significant value adding. CFEs there were profitable, while those in the RACCN struggled to break even. Household assets varied widely but, in the MBR, we found evidence that forest-based income can lift people out of poverty. Our analyses reveal that critical success factors for community forestry to reduce poverty, conserve forests and enhance equity are: secure long-term forest usufruct rights or ownership, efficient business organisation, credible advocacy, a conducive service environment, and differentiated opportunities for women, men and youth

Controllable soliton emission from a Bose-Einstein condensate

We demonstrate, through numerical simulations, the controllable emission of matter-wave bursts from a Bose-Einstein Condensate in a shallow optical dipole trap. The process is triggered by spatial variations of the scattering length along the trapping axis. In our approach, the outcoupling mechanism are atom-atom interactions and thus, the trap remains unaltered. Once emitted, the matter wave forms a robust soliton. We calculate analytically the parameters for the experimental implementation of this atomic soliton machine gun.Comment: 4 pages, 5 figure

Built Environment Factors Affecting Bike Sharing Ridership: Data-Driven Approach for Multiple Cities

Identification of factors influencing ridership is necessary for policy-making, as well as, when examining transferability and aspects of performance and reliability. In this work, a data-driven method is formulated to correlate arrivals and departures of station-based bike sharing systems with built environment factors in multiple cities. Ridership data from stations of multiple cities are pooled in one data set regardless of their geographic boundaries. The method bundles the collection, analysis, and processing of data, as well as, the model’s estimation using statistical and machine learning techniques. The method was applied on a national level in six cities in Germany, and also on an international level in three cities in Europe and North America. The results suggest that the model’s performance did not depend on clustering cities by size but by the relative daily distribution of the rentals. Selected statistically significant factors were identified to vary temporally (e.g., nightclubs were significant during the night). The most influencing variables were related to the city population, distance to city center, leisure-related establishments, and transport-related infrastructure. This data-driven method can help as a support decision-making tool to implement or expand bike sharing systems

Clonal Relatedness of Enterotoxigenic Escherichia coli (ETEC) Strains Expressing LT and CS17 Isolated from Children with Diarrhoea in La Paz, Bolivia

BACKGROUND: Enterotoxigenic Escherichia coli (ETEC) is a major cause of traveller's and infantile diarrhoea in the developing world. ETEC produces two toxins, a heat-stable toxin (known as ST) and a heat-labile toxin (LT) and colonization factors that help the bacteria to attach to epithelial cells. METHODOLOGY/PRINCIPAL FINDINGS: In this study, we characterized a subset of ETEC clinical isolates recovered from Bolivian children under 5 years of age using a combination of multilocus sequence typing (MLST) analysis, virulence typing, serotyping and antimicrobial resistance test patterns in order to determine the genetic background of ETEC strains circulating in Bolivia. We found that strains expressing the heat-labile (LT) enterotoxin and colonization factor CS17 were common and belonged to several MLST sequence types but mainly to sequence type-423 and sequence type-443 (Achtman scheme). To further study the LT/CS17 strains we analysed the nucleotide sequence of the CS17 operon and compared the structure to LT/CS17 ETEC isolates from Bangladesh. Sequence analysis confirmed that all sequence type-423 strains from Bolivia had a single nucleotide polymorphism; SNP(bol) in the CS17 operon that was also found in some other MLST sequence types from Bolivia but not in strains recovered from Bangladeshi children. The dominant ETEC clone in Bolivia (sequence type-423/SNP(bol)) was found to persist over multiple years and was associated with severe diarrhoea but these strains were variable with respect to antimicrobial resistance patterns. CONCLUSION/SIGNIFICANCE: The results showed that although the LT/CS17 phenotype is common among ETEC strains in Bolivia, multiple clones, as determined by unique MLST sequence types, populate this phenotype. Our data also appear to suggest that acquisition and loss of antimicrobial resistance in LT-expressing CS17 ETEC clones is more dynamic than acquisition or loss of virulence factors