Separable Convex Optimization with Nested Lower and Upper Constraints

We study a convex resource allocation problem in which lower and upper bounds are imposed on partial sums of allocations. This model is linked to a large range of applications, including production planning, speed optimization, stratified sampling, support vector machines, portfolio management, and telecommunications. We propose an efficient gradient-free divide-and-conquer algorithm, which uses monotonicity arguments to generate valid bounds from the recursive calls, and eliminate linking constraints based on the information from sub-problems. This algorithm does not need strict convexity or differentiability. It produces an $\epsilon$-approximate solution for the continuous problem in $\mathcal{O}(n \log m \log \frac{n B}{\epsilon})$ time and an integer solution in $\mathcal{O}(n \log m \log B)$ time, where $n$ is the number of decision variables, $m$ is the number of constraints, and $B$ is the resource bound. A complexity of $\mathcal{O}(n \log m)$ is also achieved for the linear and quadratic cases. These are the best complexities known to date for this important problem class. Our experimental analyses confirm the good performance of the method, which produces optimal solutions for problems with up to 1,000,000 variables in a few seconds. Promising applications to the support vector ordinal regression problem are also investigated

Assortative-Constrained Stochastic Block Models

Stochastic block models (SBMs) are often used to find assortative community structures in networks, such that the probability of connections within communities is higher than in between communities. However, classic SBMs are not limited to assortative structures. In this study, we discuss the implications of this model-inherent indifference towards assortativity or disassortativity, and show that this characteristic can lead to undesirable outcomes for networks which are presupposedy assortative but which contain a reduced amount of information. To circumvent this issue, we introduce a constrained SBM that imposes strong assortativity constraints, along with efficient algorithmic approaches to solve it. These constraints significantly boost community recovery capabilities in regimes that are close to the information-theoretic threshold. They also permit to identify structurally-different communities in networks representing cerebral-cortex activity regions

Reproductive biology of two bombacaceous trees in the Brazilian Central Amazon

Studies were carried out on the reproductive biology of two bombacaceous trees (Pseudobombax munguba and Ceiba pentandra) which occur in the seasonally flooded areas of the white-water river basins ('varzea') in the Amazon region. The unique pollinator of P. munguba, which has nectarless flowers, is the large-sized phyllostomid bat Phyllostomus hastatus. In contrast, the flowers of C. pentandra are visited by a wide range of nocturnal (bats, marsupials, night-monkeys, hawk moths) and diurnal (bees, wasps, hummingbirds) animals, but only the phyllostomid bats, especially Phyllostomus hastatus and Phyllostomus discolor, play a relevant role in the pollination of this mass-flowering species. Both species appear to be self-incompatible since hand self-pollinated flowers always abscised 5-8 days after pollination, whereas a proportion of cross-pollinated flowers (20-29% in P. munguba; 17% in C. pentandra) formed fruit. However, analysis of fixed pistils using fluorescence microscopy revealed that in both species the self-pollen germinated normally on the stigma and the self-pollen tubes penetrated the ovules at the same rate as the cross-pollen tubes. Mixed-pollinated flowers (self- plus cross-pollen on the stigma) also set some fruits (9-14% in P. munguba; 9% in C. pentandra). Paternity analyses using isozyme genetic markers indicated that fruits resulting from controlled mixed-pollinations set a few selfed seeds (range of 0-28% in P. munguba; ca 2% in the studied tree of C. pentandra). The multilocus estimate of the outcrossing rate (tm) was calculated for P. munguba using data from two isozyme loci of 29 parent trees and 728 progenies. The population outcrossing estimation was high (tm = 0.948) suggesting that the breeding population is large and the level of inbreeding (both uniparental and biparental) is very low. The proportion of selfed-seeds produced by two neighbouring C. pentandra trees, which flowered simultaneously, was estimated using isozyme genetic markers at 9% and 28% respectively. It is considered that a high level of genetic load is the main factor responsible for the self-sterility and the predominant outcrossing mating system observed in both species. The number of lethal equivalents per zygote estimated for each was high: average of 13.8 (minimum 6.4) in the P. munguba population, and 12.3 for the single assessed individual of C. pentandra

Extreme long-distance dispersal of the lowland tropical rainforest tree Ceiba pentandra L. (Malvaceae) in Africa and the Neotropics

Many tropical tree species occupy continental expanses of rainforest and flank dispersal barriers such as oceans and mountains. The role of long-distance dispersal in establishing the range of such species is poorly understood. In this study, we test vicariance hypotheses for range disjunctions in the rainforest tree Ceiba pentandra , which is naturally widespread across equatorial Africa and the Neotropics. Approximate molecular clocks were applied to nuclear ribosomal [ITS (internal transcribed spacer)] and chloroplast ( psb B- psb F) spacer DNA sampled from 12 Neotropical and five West African populations. The ITS ( N  = 5) and psb B- psb F ( N  = 2) haplotypes exhibited few nucleotide differences, and ITS and psb B- psb F haplotypes were shared by populations on both continents. The low levels of nucleotide divergence falsify vicariance explanations for transatlantic and cross-Andean range disjunctions. The study shows how extreme long-distance dispersal, via wind or marine currents, creates taxonomic similarities in the plant communities of Africa and the Neotropics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71417/1/j.1365-294X.2007.03341.x.pd

Propriedades mecânicas de filmes finos de carbono amorfo hidrogenados

Orientador: Francisco das Chagas MarquesDissertação (mestrado) - Universidade estadual de Campinas, Instituto de Fisica Gleb WataghinResumo: Neste trabalho realizamos o estudo das propriedades mecânicas de filmes de carbono amorfo hidrogenados. Estes filmes possuem grande interesse em várias aplicações tecnológicas como camada protetora, revestimento de discos magnéticos, camada anti-refletora, diodos fotoluminescente, entre outras. Um dos maiores problemas que limita a sua aplicação, é o alto valor de stress geralmente encontrado em filmes com alta dureza. Este stress é o principal responsável pela pouca adesão dos filmes de carbono amorfo duros. Desta forma, a produção de filmes com baixo stress, sem decréscimo da dureza, é bastante importante para a aplicação tecnológica deste material. Os filmes foram preparados utilizando um sistema de rf sputtering através da decomposição do metano. Conseguimos obter filmes com excelentes propriedades mecânicas, isto é, filmes com alta dureza, baixo stress e alta taxa de deposição ao variarmos a tensão de bias do sistema. Foram preparados filmes com dureza de 17 GPa, stress de 0.5 GPa e taxa de deposição de 2.5 Å/s. Filmes com a dureza e stress acima podem ser de grande interesse para uma possível aplicação tecnológica como camada protetora. Conseguimos também encontrar uma grande evidência do processo de sub-implantação, utilizado para explicar o processo de formação de filmes de carbono amorfo altamente tetraédricos (ta-C,ta-C:H), para filmes de a-C:H preparados através de decomposição de gases. Propomos que a estrutura dos nossos filmes consiste de uma matriz dispersa dos sítios sp2 responsáveis pela rigidez da rede. O papel principal das ligações Sp3 C-C ( carbono quaternário) é de gerar a maior contribuição do stress compressivo existente no material, como também contribuir para a dureza do filme. Realizamos também a preparação de filmes com boas propriedades mecânicas variando a pressão de metano da câmara. Obtivemos nestas condições de preparação, filmes de a-C:H duros em toda a faixa de pressão estudada. Além disto, conseguimos uma considerável redução do stress, cerca de 50%, sem um significante decréscimo da dureza do material. Encontramos também que o coeficiente de dilatação térmica e o módulo biaxial permanecem constantes em toda a faixa de pressão estudada. O aumento no gap de Tauc e da área da vibração C-H stretching sugere um aumento no número de ligações C-H na estrutura dos filmes com o aumento da pressão. Conseguimos obter filmes com dureza de 17 GPa, stress de 1.3 Gpa, e com uma taxa de deposição relativamente alta de 2 Å/s. Dependendo da espessura, a redução do stress obtida já é baixa o suficiente para a preparação de filmes estáveis. Apesar do stress deste filme (1.3 GPa) ser maior quando comparado com o stress obtido dos filmes preparados a alto bias (0.56 GPa), estes possuem um valor de gap ótico mais alto o que viabiliza a sua utilização como camada anti-refletora ou revestimento de peças óticasAbstract: In this work we have developed a study on the mechanical properties of hydrogenated amorphous carbon films. These films have numerous potential applications like wear resistant coatings, magnetic recording disk, antireflective coatings, photoluminescent diode, etc. One of the main problems that hinders these applications is the high internal stress, usually present in films with high hardness. It is well known that high stress is responsible for the poor adhesion of hard amorphous carbon films. Therefore, the production of films with low stress is extremely important for technological application. In this work, the films were prepared in a conventional rf sputtering system through methane gas decomposition. The fi1ms produced as a function of the bias voltage possessed excellent mechanical properties: high hardness, low stress and high deposition rate. We have been able to prepare a fi1m with hardness of 17 GPa, stress as low as 0.5 GPa and with a deposition rate of 2.5 Å/s. A film with these properties can be of significant interest for technological application as hard coating. Also, we found a strong evidence that the subimplantation process, used to explain the formation of highly tetrahedral amorphous carbon films (ta-C,ta-C:H), is also valid for a-C:H films deposited by methane plasma decomposition. We proposed that the rigidity of our films is basically provided by a matrix of dispersed cross-linked Sp2 sites. The main role of the quaternary carbon (Sp3 C-C) would be to strain the cross-linked structure, providing the major contribution to the compressive stress presented in the films, and also a small improvement of the material hardness. We have also obtained films with good mechanical properties by varying the methane gas pressure. Remarkable reductions of the film stress, of about 50%, without a significant decrease of the film hardness were obtained. The thermal expansion coefficient and the biaxial modulus remained constant in alI pressure range. The increase in both Tauc gap and C-H stretching area suggests a increase of the number of C-H bonds in the film structure as the methane pressure increases. We also prepared films with hardness of 17 GPa, stress of 1.3 GPa and a deposition rate of 2 Å/s. The stress of these films are sufficient low for a possible application of these material as hard coating. Although this stress is higher than the stress of the films produced at high bias, these films have a higher value of the Tauc gap, which provides a potential application of these films as anti-reflecting coatingsMestradoFísicaMestre em Físic

Genetics of cytosolic phosphoglucose isomerase (PGI) variation in the Amazonian tree Pseudobombax munguba (Bombacaceae)

A genetic analysis of cytosolic phosphoglucose isomerase (PGI) variation in the tropical tree Pseudobombax munguba (Bombacaceae) was carried out in one population from Central Amazon. It was shown that cytosolic PGI variation is controlled by two diallelic loci (Pgi-2 and Pgi-3). All nine possible enzyme phenotypes produced by allelic variation at these two loci were easily identified on gels stained for PGI. Progeny analysis from cross-pollinated families revealed that the two loci assorted independently and exhibited disomic inheritance, suggesting that allopolyploidy may have been the cause of the duplication of the cytosolic PGI gene in this species. ©1996 The Genetical Society of Great Britain

Flexible mating system in a logged population of Swietenia macrophylla King (Meliaceae): implications for the management of a threatened neotropical tree species.

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