Collective dynamic properties in simple crystals: Influence of the structural disorder

Collective dynamic properties in Lennard-Jones crystals are investigated by molecular dynamics simulation. The study is focused on properties such as the dynamic structure factors, the longitudinal and transverse currents and the density of states. The influence on these properties of the structural disorder is analyzed by comparing the results for one-component crystals with those for liquids and supercooled liquids at analogous conditions. The effects of species-disorder on the collective properties of binary crystals are also discussed.

Absence of collective effects in Heisenberg systems with localized magnetic moments

Existence of collective effects in magnetic coupling in ionic solids is studied by mapping spin eigenstates of the Heisenberg and exact nonrelativistic Hamiltonians on cluster models representing KNiF3, K2NiF4, NiO, and La2CuO4. Ab initio techniques are used to estimate the Heisenberg constant J. For clusters with two magnetic centers, the values obtained are about the same for models having more magnetic centers. The absence of collective effects in J strongly suggests that magnetic interactions in this kind of ionic solids are genuinely local and entangle only the two magnetic centers involved.

Relativistic Thomas-Fermi description of collective modes in droplets of nuclear matter

Isoscalar collective modes in a relativistic meson-nucleon system are investigated in the framework of the time-dependent Thomas-Fermi method. The energies of the collective modes are determined by solving consistently the dispersion relations and the boundary conditions. The energy weighted sum rule satisfied by the models considered allows the identification of the giant resonances. The percentage of the energy weighted sum rule exhausted by the collective modes is in agreement with experimental data, but the agreement with the energy of the modes depends on the model considered.

Isolation and characterization of broad spectrum bacteriophages lytic to Vibrio harveyi from shrimp farms of Kerala, India

Of 33 phages isolated from various shrimp farms in Kerala, India, six were segregated to have broad spectrum lytic efficiency towards 87 isolates of Vibrio harveyi with cross-infecting potential to a few other important aquaculture pathogens. They were further tested on beneficial aquaculture micro-organisms such as probiotics and nitrifying bacterial consortia and proved to be noninfective. Morphological characterization by transmission electron microscopy (TEM) and molecular characterization by RAPD and SDS-PAGE proved them distinct and positioned under Caudovirales belonging to Myoviridae and Siphoviridae

Studies on collective excitations of quasi-two-dimensional Bose-Einstein condensate

Theory Division Department of Physics

Factors influencing a conversion to organic farming in Nepalese tea farms

Organic agriculture in developing countries has increased in past decades especially due to the high demand of organic products in developed countries. The rate of conversion to organic production in Nepal, however, is observed much slower than expected. This study investigates factors that determine the conversion to organic production using Nepalese tea producers as a case study. A survey of 181 farmers was conducted in the Ilam and Panchthar district of Nepal, among which 86 were organic farmers and 95 were conventional farmers. A discriminant analysis was used to identify socio-economic characteristics that distinguish conventional and organic farmers. Results from the estimated discriminant function suggest that farmers located in a distance from regional markets, older in age, better trained, affiliated with institutions and having larger farms are more likely to adopt organic production. Similarly, a factor analysis shows that environmental awareness, bright market prospects, observable economic benefit and health consciousness are the major factors influencing farmers’ decisions on the conversion to organic production. While planning programs for the development of the organic tea sector in Nepal, policy makers should consider the support of farmers’ institutions, provision of training to farmers and raise farmers’ awareness about the environmental, economic and health benefits of organic farming.

Producers’ motivation for collective action for kola production and marketing in Cameroon

Collective action has been used as a strategy to improve the benefits of smallholder producers of kola nuts in Cameroon. Despite demonstrated benefits, not all producers are involved in the collective action. The presented study used a modified Technology Acceptance Model (TAM) namely the Collective Action Behaviour model (CAB model) to analyse kola producers’ motivation for collective action activities. Five hypotheses are formulated and tested using data obtained from 185 farmers who are involved in kola production and marketing in theWestern highlands of Cameroon. Results which were generated using Partial Least Squares (PLS) approach for Structural Equation Modelling (SEM) showed that farmers’ intrinsic motivators and ease of use influenced their behavioural intent to join a group marketing activities. The perceived usefulness that was mainly related to the economic benefits of group activities did not influence farmers’ behavioural intent. It is therefore concluded that extension messages and promotional activities targeting collective action need to emphasise the perceived ease of use of involvement and social benefits associated with group activities in order to increase farmers’ participation.

Soil, water and nutrient loss under conventional and organic vegetable production managed in small farms

Agricultural systems with conventional tillage and intensive use of agrochemicals, especially those on high slopes and with shallow soils, have the potential to release pollutants. This study aimed at evaluating the soil, water and nutrient lost via agricultural runoff in large plots (small catchments) under conventional and organic farming of vegetables as well as under forest (control) system in a Cambisol in the Campestre catchment. Samples of runoff were collected biweekly for one year through a Coshocton wheel. The soil and water losses from the conventional farming were 218 and 6 times higher, respectively, than forest. Under organic farming the soil and water losses were 12 and 4 times higher, respectively, than forest. However the soil losses (0.5 to 114 kg ha^(−1) year^(−1)) are considered low in agronomy but environmentally represent a potential source of surface water contamination by runoff associated pollutants. The concentrations and losses of all forms of phosphorus (P) were higher in the conventional system (9.5, 0.9 and 0.3 mg L^(−1) of total P for conventional, organic and forest systems, respectively), while the organic system had the highest concentrations and losses of soluble nitrogen (4.7, 38.6 and 0.4 mg L^(−1) of NO_3-N, respectively). The percentage of bioavailable P was proportionally higher in the organic system (91% of total P lost was as bioavailable P), indicating greater potential for pollution in the short term.

Dairy farms typology and management of animal genetic resources in the peri-urban zone of Bamako (Mali)

Facing growth in demand, dairy production in peri-urban areas of developing countries is changing rapidly. To characterise this development around Bamako (Mali), this study establishes a typology of dairy production systems with a special focus on animal genetic resources. The survey included 52 dairy cattle farms from six peri-urban sites. It was conducted in 2011 through two visits, in the dry and harvest seasons. The median cattle number per farm was 17 (range 5-118) and 42% of farmers owned cropland (8.3 +/- 7.3 ha, minimum 1 ha, maximum 25 ha). Feeding strategy was a crucial variable in farm characterisation, accounting for about 85% of total expenses. The use of artificial insemination and a regular veterinary follow-up were other important parameters. According to breeders’ answers, thirty genetic profiles were identified, from local purebreds to different levels of crossbreds. Purebred animals raised were Fulani Zebu (45.8%), Maure Zebu (9.2%), Holstein (3.0%), Azawak Zebu (1.3%), Mere Zebu (0.5%) and Kuri taurine (0.1%). Holstein crossbred represented 30.5% of the total number of animals (19.0% Fulani-Holstein, 11.2% Maure-Holstein and 0.3% Kuri-Holstein). Montbéliarde, Normande and Limousin crossbreds were also found (6.6%, 0.7% and 0.3%, respectively). A multivariate analysis helped disaggregate the diversity of management practices. The high diversity of situations shows the need for consideration of typological characteristics for an appropriate intervention. Although strongly anchored on local breeds, the peri-urban dairy systems included a diversity of exotic cattle, showing an uncoordinated quest of breeders for innovation. Without a public intervention, this dynamic will result in an irremediable erosion of indigenous animal genetic resources.

Psychometric properties of the Spanish version of the Collective Efficacy Questionnaire for Sports

Resumen tomado de la publicaci??n

Spanish adaptation of the Adolescents' Perceived Collective Family Efficacy Scale

Resumen tomado de la publicaci??n

Does the collective strategy ensure the small and medium sized perdurability?

El posicionamiento estratégico se define como el punto de partida de toda reflexión de la organización (por más pequeña que sea) que pretende poner un lugar dentro de la empresa el”give back” del propio rendimiento. En el caso de la estrategia colectiva, no sólo hay una visión de un dirigente (manager), al contrario hay una gran cantidad de visiones de diferentes gestores, que tendrá que tomar decisiones comunes beneficiosas para sus propios intereses y el común de los intereses de cada empresa. Por lo tanto, es esencial que la situación actual y los objetivos a alcanzar estén claramente definidos desde el comienzo de la elaboración de la estrategia, para evitar las posibles divergencias que puedan poner en riesgo la coherencia de la estrategia. Con los problemas encontrados en la PYME francesa, como el inicio de la actividad, los problemas financieros, la integración organizativa y la competencia y el desarrollo de productos, la estrategia colectiva aparece como una posible solución que permite a la PYME perdurar en el tiempo. En Francia, impulsada por el Gobierno y otras instituciones financieras y administrativas, esta estrategia ha conseguido resultados que antes no se habían pensado, como lo demuestra el estudio de modelo urbano el cuál es presentado en esta investigación. Esta es la razón y el por qué se eligió este tema.

Six Degrees: The New Science of Networks (Collective Dynamics Group ISERP -- Columbia University) Course Syllabus

Six Degrees: The New Science of Networks (Sociology, W3233, Spring 2006) Original URL: http://cdg.columbia.edu/cdg/courses/spring06/sixDegrees/syllabus.jsp