2,092 research outputs found
Efficient Computation of Multiple Density-Based Clustering Hierarchies
HDBSCAN*, a state-of-the-art density-based hierarchical clustering method,
produces a hierarchical organization of clusters in a dataset w.r.t. a
parameter mpts. While the performance of HDBSCAN* is robust w.r.t. mpts in the
sense that a small change in mpts typically leads to only a small or no change
in the clustering structure, choosing a "good" mpts value can be challenging:
depending on the data distribution, a high or low value for mpts may be more
appropriate, and certain data clusters may reveal themselves at different
values of mpts. To explore results for a range of mpts values, however, one has
to run HDBSCAN* for each value in the range independently, which is
computationally inefficient. In this paper, we propose an efficient approach to
compute all HDBSCAN* hierarchies for a range of mpts values by replacing the
graph used by HDBSCAN* with a much smaller graph that is guaranteed to contain
the required information. An extensive experimental evaluation shows that with
our approach one can obtain over one hundred hierarchies for the computational
cost equivalent to running HDBSCAN* about 2 times.Comment: A short version of this paper appears at IEEE ICDM 2017. Corrected
typos. Revised abstrac
Electrostatics of electron-hole interactions in van der Waals heterostructures
The role of dielectric screening of electron-hole interaction in van der
Waals heterostructures is theoretically investigated. A comparison between
models available in the literature for describing these interactions is made
and the limitations of these approaches are discussed. A simple numerical
solution of Poissons equation for a stack of dielectric slabs based on a
transfer matrix method is developed, enabling the calculation of the
electron-hole interaction potential at very low computational cost and with
reasonable accuracy. Using different potential models, direct and indirect
exciton binding energies in these systems are calculated within Wannier-Mott
theory, and a comparison of theoretical results with recent experiments on
excitons in two-dimensional materials is discussed.Comment: 10 pages, 8 figure
Produção e distribuição sazonal de litter em áreas de caatinga sob diferentes manejos.
Resumo: O litter compreende restos vegetais e animais. Sua presença confere proteção ao solo evitando o efeito negativo das enxurradas, mantendo a temperatura e estrutura do solo. Este trabalho objetivou quantificar a produção e distribuição de litter em áreas de caatinga raleada e não manipulada. Três áreas foram utilizadas: raleada para fins pastoris, raleada para fins apícolas e não manipulada. A produção foi obtida a partir do lançamento de molduras e 1,0x0,25m em diferentes épocas do ano de 2012. O litter foi fracionado manualmente em seus componentes e determinados suas proporções da massa total. A área não manipulada apresentou maior produção de litter, 5.714,35 Kg/ha enquanto a área de Caatinga raleada para fins apícolas a menor produção, 3.921,21 Kg/ha. A miscelânea foi a fração do litter que apresentou maior representatividade chegando a responder por 50% de toda a produção. A produção de litter de uma área nativa pode ser semelhante a uma área raleada. A produção tem relação direta com a precipitação. Esta mostrou sazonalidade na produção total, contrariando suas frações que mantiveram-se equilibrados durante todo o ano. [Seasonal production and distribution of litter in different areas under caatinga managements]. Abstract: The litter includes plant and animal remains. Its presence confers protection to the ground avoiding the negative effect of floods, keeping the temperature and soil structure. This study aimed to quantify the production and distribution of litter in areas of thinned caatinga and not manipulated. Three areas were used for grazing purposes thinned, thinned for apiculture and not manipulated. The production was obtained from the launch of frames and 1.0 x0, 25m at different times of the year 2012. The litter was manually fractionated into its components, and certain proportions of their total mass. The area had not manipulated greater production of litter, 5714.35 kg / ha while the area of Caatinga thinned for apiculture lower production, 3921.21 kg / ha. The smorgasbord was the fraction of the litter with the highest representation coming to account for 50% of all production. The production of litter from an area native can be similar to a thinned area. The production is directly related to precipitation. The total production of litter showed seasonality, contradicting its fractions which remained balanced throughout the year
Uma abordagem com cálculo fracionário ao transporte de contaminantes em solos tropicais lateríticos.
Uso do orçamento forrageiro em abordagem participativa para produção de caprinos no bioma caatinga.
Resumo: O uso do orçamento forrageiro (OF) com enfoque participativo visa envolver agricultores no processo de construção de técnicas que possam ser facilmente utilizadas para o manejo sustentável dos recursos naturais. O objetivo deste trabalho foi testar OF como instrumento para planejamento do rebanho caprino. A experiência foi conduzida em área individual de 11ha, em assentamento no sertão do Apodi (RN). A área foi composta por cultivo de algodão agroecológico, sistema agrossilvipastoril e pasto nativo. O rebanho foi de vinte animais. OF foi realizado em três etapas: levantamento da produção de massa seca total de forragem disponível, avaliação do efetivo animal e planejamento. As informações do levantamento determinaram o tempo máximo de uso da área para manter as metas de ganho de peso para cabritos e manutenção de peso dos adultos. As práticas agroecológicas aumentaram a oferta de forragem. Houve manutenção do peso das cabras e ganhos de peso nas novilhas. Os cabritos ganharam peso de forma linear. O monitoramento permitiu confirmar que a ferramenta do orçamento forrageiro foi efetiva em auxiliar no planejamento zootécnico do rebanho no semiárido. [Forage budget on participatory approach to goat production in caatinga biome]. Abstract: Forage budget (FB) using participatory approach had been used to include smallholders in technology generation process and improving transfer technology for others. This research was carried out to test FB as a tool to make a planning for goat production system in Brazilian semi arid land. In an individual settlement area about 11 ha was implemented it. There were agroecological cotton system, agrossilvipastoral and native vegetation there. There were 20 animal in the area. FB was implemented in three phases: quantification of forage biomass total and available, herd evaluation and planning. It was determinate a maximum time to keep animal in the land using information from planning that preview as goal keep weight in goats and gain weight in kids. Ecological practices improved amount of forage. There was possible keep weight in goats. Young goats had gained weight. All kids gained weight during experimental period. Monitoring zootechnical aspects were effective to ensure forage budget like a good tool to help smallholders in sustainable planning use natural resources
GPS-based CERN-LNGS time link for Borexino
We describe the design, the equipment, and the calibration of a new GPS based
time link between CERN and the Borexino experiment at the Gran Sasso Laboratory
in Italy. This system has been installed and operated in Borexino since March
2012, and used for a precise measurement of CNGS muon neutrinos speed in May
2012. The result of the measurement will be reported in a different letter.Comment: 13 pages, 11 figure
Recomendação de diferentes épocas de colheita para cultivares de mandioca tipo Indústria em Alagoas.
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