Recursive McCormick Linearization of Multilinear Programs

Linear programming (LP) relaxations are widely employed in exact solution methods for multilinear programs (MLP). One example is the family of Recursive McCormick Linearization (RML) strategies, where bilinear products are substituted for artificial variables, which deliver a relaxation of the original problem when introduced together with concave and convex envelopes. In this article, we introduce the first systematic approach for identifying RMLs, in which we focus on the identification of linear relaxation with a small number of artificial variables and with strong LP bounds. We present a novel mechanism for representing all the possible RMLs, which we use to design an exact mixed-integer programming (MIP) formulation for the identification of minimum-size RMLs; we show that this problem is NP-hard in general, whereas a special case is fixed-parameter tractable. Moreover, we explore structural properties of our formulation to derive an exact MIP model that identifies RMLs of a given size with the best possible relaxation bound is optimal. Our numerical results on a collection of benchmarks indicate that our algorithms outperform the RML strategy implemented in state-of-the-art global optimization solvers.Comment: 22 pages, 11 figures, Under Revie

Stereotactic Radiosurgery for Management of Cavernous Malformations

Cavernous malformations (CMs) are abnormal vascular formations of the brain with an estimated incidence of 0.4%-0.8% in the general population.1 CMs have the potential to cause significant morbidity, and have been associated with epileptic seizures, intracranial hemorrhage, and focal neurological deficits.2 Management options include non-treatment, surgical resection, and radiosurgery. We review here the efficacy of different management strategies for cavernous malformations and highlight the specific role of radiosurgery. One of the major complications of cerebral cavernous malformations is intracranial hemorrhage. To optimize patient treatment, it is beneficial to be able to identify patients that are at an increased risk of developing a hemorrhage and would most benefit from intervention. The overall rate of hemorrhage in patients with CMs has been estimated to be 2.25%.3 The rate of hemorrhage, however, is significantly affected by the initial symptom presentation. Patients presenting with a hemorrhage have significantly higher rates of rehemorrhage compared to patients presenting due to incidental findings.3,4 Flemming et al. found that patients presenting with hemorrhage had an overall annual rate of hemorrhage of 6.19% compared to patients presenting without hemorrhage of 0.33%. With increasing use of MR imaging, the percentage of cavernous malformations found incidentally approaches 40%.1 Because the risk of hemorrhage is low in patients with CMs found incidentally, surgical or radiosurgery management may not be indicated. In contrast, patients presenting with symptoms of hemorrhage should be considered for therapeutic intervention due to a high risk for subsequent hemorrhage. One option for the management of cavernous malformations is surgical intervention by CM resection. There is conflicting evidence in the literature regarding the effectiveness of CM resection, likely due to different methodologies used for determining efficacy. When post-operative outcomes are compared to pre-operative values, significant improvement is observed as demonstrated by improvements in the modified Rankin scale and decreased annual hemorrhage rate.5,6 However, the results are limited by the fact that studies did not include a control group of patients that did not receive surgery. A recent retrospective study by Moultrie and colleagues compared the outcome of patients treated with surgical to conservative management. Patients who underwent CM resection had worsened short-term disability scores, increased risk of developing intracranial hemorrhage, and new focal neurologic deficits.

First complete pterosaur from the Afro-Arabian continent : insight into pterodactyloid diversity

Despite being known from every continent, the geological record of pterosaurs, the first group of vertebrates to develop powered flight, is very uneven, with only a few deposits accounting for the vast majority of specimens and almost half of the taxonomic diversity. Among the regions that stand out for the greatest gaps of knowledge regarding these flying reptiles, is the Afro-Arabian continent, which has yielded only a small number of very fragmentary and incomplete materials. Here we fill part of that gap and report on the most complete pterosaur recovered from this continent, more specifically from the Late Cretaceous (~95 mya) Hjoûla Lagerstätte of Lebanon. This deposit is known since the Middle Ages for the exquisitely preserved fishes and invertebrates, but not for tetrapods, which are exceedingly rare. Mimodactylus libanensis gen. et sp. nov. differs from the other Afro-Arabian pterosaur species named to date and is closely related to the Chinese species Haopterus gracilis, forming a new clade of derived toothed pterosaurs. Mimodactylidae clade nov. groups species that are related to Istiodactylidae, jointly designated as Istiodactyliformes (clade nov.). Istiodactyliforms were previously documented only in Early Cretaceous sites from Europe and Asia, with Mimodactylus libanensis the first record in Gondwana

Cambios en las comunidades bacterianas de suelo luego de una contaminación con hexadecano

This paper reports on changes in the soil bacterial community from a petroleum zone of Argentina. Changes were observed in a microcosm test which was subject to contamination with hexadecane. The determination of hydrocarbons and bacterial counts were performed weekly. Changes in bacterial diversity were determined by the analysis of membrane fatty acids (FAMEs), identified and quantified by gas chromatography using according to MIDI parameters. It was observed that contamination with hexadecane cause a disturbance in the soil leading to a change in the bacterial community structure.El presente trabajo informa sobre los cambios en la comunidad bacteriana de un suelo proveniente de una zona hidrocarburífera de Argentina. Los cambios se observaron en un ensayo de microcosmo el cual fue sometido a contaminación con hexadecano. La determinacion de hidrocarburos y los recuentos bacterianos fueron realizados semanalmente. Los cambios en la diversidad bacteriana se determinaron por la el análisis de los ácidos grasos de membrana (FAMEs); identificándose y cuantificándose por cromatografía gaseosa utilizando los parámetros según MIDI. Se observó que la contaminación con hexadecano causa un disturbio en el suelo que conduce a un cambio en la estructura de la comunidad bacteriana

Herd-level risk for Salmonella culture positive status in slaughtered pigs.

Quantitative definition of risk factors is needed for farms to develop programs and procedures to reduce Salmonella shedding economically and reliably. It is essential that this information be available to producers before full implementation of proposed Salmonella reduction regulations. Producers should then be able to retain market access and choose informed interventions while avoiding unnecessary costs

Identification of Methanoculleus spp. as active methanogens during anoxic incubations of swine manure storage tank samples

Methane emissions represent a major environmental concern associated with manure management in the livestock industry. A more thorough understanding of how microbial communities function in manure storage tanks is a prerequisite for mitigating methane emissions. Identifying the microorganisms that are metabolically active is an important first step. Methanogenic archaea are major contributors to methanogenesis in stored swine manure, and we investigated active methanogenic populations by DNA stable isotope probing (DNA-SIP). Following a preincubation of manure samples under anoxic conditions to induce substrate starvation, [U-¹³C] acetate was added as a labeled substrate. Fingerprint analysis of density-fractionated DNA, using length-heterogeneity analysis of PCR-amplified mcrA genes (encoding the alpha subunit of methyl coenzyme M reductase), showed that the incorporation of ¹³C into DNA was detectable at in situ acetate concentrations (~7g/liter). Fingerprints of DNA retrieved from heavy fractions of the ¹³C treatment were primarily enriched in a 483-bp amplicon and, to a lesser extent, in a 481-bp amplicon. Analyses based on clone libraries of the mcrA and 16S rRNA genes revealed that both of these heavy DNA amplicons corresponded to Methanoculleus spp. Our results demonstrate that uncultivated methanogenic archaea related to Methanoculleus spp. were major contributors to acetate-C assimilation during the anoxic incubation of swine manure storage tank samples. Carbon assimilation and dissimilation rate estimations suggested that Methanoculleus spp. were also major contributors to methane emissions and that the hydrogenotrophic pathway predominated during methanogenesis