Efficient Algorithms for Large Scale Global Optimization: Lennard-Jones Clusters

A stochastic global optimization method is applied to the challenging problem of finding the minimum energy conformation of a cluster of identical atoms interacting through the Lennard-Jones potential. The method proposed incorporates within an already existing and quite successful method, monotonic basin hopping, a two-phase local search procedure which is capable of significantly enlarging the basin of attraction of the global optimum. The experiments reported confirm the considerable advantages of this approach, in particular for all those cases which are considered in the literature as the most challenging ones, namely 75, 98, 102 atoms. While being capable of discovering all putative global optima in the range considered, the method proposed improves by more than two orders of magnitude the speed and the percentage of success in finding the global optima of clusters of 75, 98, 102 atoms.     

Simulated Annealing Algorithms for Continuous Global Optimization: Convergence Conditions

In this paper, simulated annealing algorithms for continuous global optimization are considered. After a review of recent convergence results from the literature, a class of algorithms is presented for which strong convergence results can be proved without introducing assumptions which are too restrictive. The main idea of the paper is that of relating both the temperature value and the support dimension of the next candidate point, so that they are small at points with function value close to the current record and bounded away from zero otherwise.     

A spectro-microscopic study of the reactive phase separation of Au + Pd and O on Rh(1 1 0)

Reorganization of Au + Pd submonolayers on a Rh(1 1 0) surface occurring during the water formation reaction has been observed and characterized by low energy electron microscopy (LEEM) and X-ray photoemission electron microscopy (XPEEM). The results demonstrate segregation of Au + Pd and oxygen into separate surface phases, the morphology and size of the O and Au + Pd patterns being governed by the reaction parameters and adsorbate coverage. At moderate Au + Pd coverages and temperatures in the range 760-860 K, lamellar periodic Au + Pd/O micro-structures are generated. The results are interpreted in terms of kinetic and thermodynamic considerations.     

Undominated d.c. Decompositions of Quadratic Functions and Applications to Branch-and-Bound Approaches

In this paper we analyze difference-of-convex (d.c.) decompositions for indefinite quadratic functions. Given a quadratic function, there are many possible ways to decompose it as a difference of two convex quadratic functions. Some decompositions are dominated, in the sense that other decompositions exist with a lower curvature. Obviously, undominated decompositions are of particular interest. We provide three different characterizations of such decompositions, and show that there is an infinity of undominated decompositions for indefinite quadratic functions. Moreover, two different procedures will be suggested to find an undominated decomposition starting from a generic one. Finally, we address applications where undominated d.c.d.s may be helpful: in particular, we show how to improve bounds in branch-and-bound procedures for quadratic optimization problems.     

Geometry‐Related Children's Literature Improves the Geometry Achievement and Attitudes of Second‐Grade Students

Use of mathematics‐related literature can engage students' interest and increase their understanding of mathematical concepts. A quasi‐experimental study of two second‐grade classrooms assessed whether daily inclusion of geometry‐related literature in the classroom improved attitudes toward geometry and achievement in geometry. Consistent with the hypothesis, only the students in the classroom with a strong emphasis on geometry‐related children's literature showed a significant improvement in their attitudes about geometry over time. While both classes improved their geometry performance over the 4 weeks of the study, the class with a strong emphasis on geometry‐related literature improved significantly more (51.2%) than the control class (33.47%). Children's literature can provide a useful and interesting context in which students can develop their understanding of geometry.     

Speciation of metal(loid)s in environmental samples by X-ray absorption spectroscopy: A critical review

Element specificity is one of the key factors underlying the widespread use and acceptance of X-ray absorption spectroscopy (XAS) as a research tool in the environmental and geo-sciences. Independent of physical state (solid, liquid, gas), XAS analyses of metal(loid)s in complex environmental matrices over the past two decades have provided important information about speciation at environmentally relevant interfaces (e.g. solid–liquid) as well as in different media: plant tissues, rhizosphere, soils, sediments, ores, mineral process tailings, etc. Limited sample preparation requirements, the concomitant ability to preserve original physical and chemical states, and independence from crystallinity add to the advantages of using XAS in environmental investigations. Interpretations of XAS data are founded on sound physical and statistical models that can be applied to spectra of reference materials and mixed phases, respectively. For spectra collected directly from environmental matrices, abstract factor analysis and linear combination fitting provide the means to ascertain chemical, bonding, and crystalline states, and to extract quantitative information about their distribution within the data set. Through advances in optics, detectors, and data processing, X-ray fluorescence microprobes capable of focusing X-rays to micro- and nano-meter size have become competitive research venues for resolving the complexity of environmental samples at their inherent scale. The application of μ-XANES imaging, a new combinatorial approach of X-ray fluorescence spectrometry and XANES spectroscopy at the micron scale, is one of the latest technological advances allowing for lateral resolution of chemical states over wide areas due to vastly improved data processing and detector technology.     

Superhydrophobic-Superhydrophilic Micropatterning: Towards Genome-on-a-Chip Cell Microarrays

High-density cell microarrays based on superhydrophilic microspots separated by superhydrophobic barriers have been realized. The microspots absorb water solutions, while the barriers prevent cross-contamination, thus allowing the spots to be used as reservoirs for transfection mixtures and preventing cell proliferation and cell migration between the microspots. The picture shows four cell types after two days of culturing on the microarray.     

Anthraquinone profile, antioxidant and antimicrobial properties of bark extracts of Rhamnus catharticus and R. orbiculatus

The anthraquinone profile, antioxidant and antimicrobial activities as well as the total phenol and total flavonoid contents were determined in methanol extracts of the barks of Rhamnus catharticus L. and R. orbiculatus Bornm. The most abundant anthraquinone derivatives in R. catharticus were physcion (67.8%) and emodin (26.2%), while R. orbiculatus contained mostly physcion (81.3%) and chrysophanol (14.6%). R. catharticus displayed better activity in the beta-carotene-linoleic acid assay, as well as chelating activity, whereas its activity in the reducing power assay was significantly lower than that of R. orbiculatus. Both methanol extracts showed antimicrobial activity against all microbial species tested (Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, Candida albicans, Aspergillus niger, Microsporum gypseum) with MIC values either equal to or lower than 2.50 mg/mL. R. catharticus and R. orbiculatus contained several anthranoid aglycones and their bark extracts demonstrated notable antioxidant and antimicrobial properties. The results obtained indicate the medicinal potential of these two species.