A Branch and Bound approach for truss topology design problems with valid inequalities

One of the classical problems in the structural optimization field is the Truss Topology Design Problem (TTDP) which deals with the selection of optimal configuration for structural systems for applications in mechanical, civil, aerospace engineering, among others. In this paper we consider a TTDP where the goal is to find the stiffest truss, under a given load and with a bound on the total volume. The design variables are the cross-section areas of the truss bars that must be chosen from a given finite set. This results in a large-scale non-convex problem with discrete variables. This problem can be formulated as a Semidefinite Programming Problem (SDP problem) with binary variables. We propose a branch and bound algorithm to solve this problem. In this paper it is considered a binary formulation of the problem, to take advantage of its structure, which admits a Knapsack problem as subproblem. Thus, trying to improve the performance of the Branch and Bound, at each step, some valid inequalities for the Knapsack problem are included

Columnar Molecular Aggregation In The Aqueous Solutions Of Disodium Cromoglycate

Stack, chimneylike, and threadlike assemblies have previously been proposed for the structure of disodium cromoglycate (DSCG) aggregates in aqueous solutions. The results of the synchrotron x-ray scattering investigations reported here reveal the formation of simple columnar assemblies with pi-pi stacking at a separation of 3.4 angstrom between the DSCG molecules. Lateral separation between the assemblies is concentration and temperature dependent, varying from similar to 35 to 42 angstrom in the orientationally ordered nematic (N) phase and from 27 to 32 angstrom in the columnar or middle (M) phase having long range lateral positional order. The assemblies\u27 length depends on concentration and consists of similar to 23 molecules in the N phase, becoming three to ten times larger in the M phase. The scission energy is concentration dependent in the N phase with values similar to 7.19 +/- 0.14 k(B)T (15 wt%), 2.73 +/- 0.4 k(B)T (20 wt%), and 3.05 +/- 0.2 k(B)T (25 wt%). Solutions of all concentrations undergo a spinodal decomposition at temperatures above similar to 40 degrees C, resulting in DSCG-rich regions with the M phase and water-rich regions in the N and isotropic phases

Theory of orientational ordering in colloidal molecular crystals

Freezing of charged colloids on square or triangular two-dimensional periodic substrates has been recently shown to realize a rich variety of orientational orders. We propose a theoretical framework to analyze the corresponding structures. A fundamental ingredient is that a non spherical charged object in an electrolyte creates a screened electrostatic potential that is anisotropic at any distance. Our approach is in excellent agreement with the known experimental and numerical results, and explains in simple terms the reentrant orientational melting observed in these so called colloidal molecular crystals. We also investigate the case of a rectangular periodic substrate and predict an unusual phase transition between orientationnaly ordered states, as the aspect ratio of the unit cell is changed.Comment: 4 pages, to appear in Phys. Rev. Let

Uji Senyawa Taurin Sebagai Antikanker Terhadap Jumlah Sel-Sel Leukosit Dan Sel-Sel Eritrosit Mencit (Mus musculus L.) yang Diinduksi Benzo (Α) Pyren Secara In Vivo

The aim of this research was to determine the effect of taurine supplementation on the totalcount of leucocyte cells and erythrocyte cells of mice that have been induced to benzo (α)pyrene in vivo. The parameters of this experiment were the total count of leucocyte cells anderythrocyte cells of mice (Mus musculus L.). This experiment was conducted in a completerandomized design by using six treatments, each in five replications. The mice were dividedinto six groups. Group I used as control were not given any treatment. Group II were given0,2 mL of oleum olevarum (olive oil) orally to the end of the experiment. Group III wereinduced to benzo (α) pyrene without being given any taurine. Group IV were given 7,8mg/bw of taurine before being induced to benzo (α) pyrene. Group V were given 7,8 mg/bwof taurine after being induced to benzo (α) pyrene. Group VI were given 15,6 mg/bw oftaurine after being induced to benzo (α) pyrene. Mice of group III, V, and VI were injectedwith 0,5 mL of benzo (α) pyrene solution every day for 10 days on their subcutant tissue forthe purpose of a nodule being formed in this area. It was then continued by giving taurineorally for 15 days. In the final treatment, mice blood was taken to count the leucocyte cellsand erythrocyte cells. The data were analyzed using ANOVA (Analysis of Variance) thencontinued by calculating least significant difference at 5 per cent level of significance. Theresults indicated that taurine had the ability to reduce leucocyte cells into its normalquantity, and was able to increase the number of erythrocyte cells of mice suffered fromleukaemia back to normal.Key words: benzo (α) pyrene, leukaemia, leucocyte, mice , taurin

Measurement of the conductance of a hydrogen molecule

Recent years have shown steady progress in research towards molecular electronics [1,2], where molecules have been investigated as switches [3-5], diodes [6], and electronic mixers [7]. In much of the previous work a Scanning Tunnelling Microscope was employed to address an individual molecule. As this arrangement does not provide long-term stability, more recently metal-molecule-metal links have been made using break junction devices [8-10]. However, it has been difficult to establish unambiguously that a single molecule forms the contact [11]. Here, we show that a single H2 molecule can form a stable bridge between Pt electrodes. In contrast to results for other organic molecules, the bridge has a nearly perfect conductance of one quantum unit, carried by a single channel. The H2-bridge provides a simple test system and a fundamental step towards understanding transport properties of single-molecule devices.Comment: 6 pages, 4 figure

Lagrangian relaxation bounds for a production-inventory-routing problem

We consider a single item Production-Inventory-Routing problem with a single producer/supplier and multiple retailers. Inventory management constraints are considered both at the producer and at the retailers, following a vendor managed inventory approach, where the supplier monitors the inventory at retailers and decides on the replenishment policy for each retailer. We assume a constant production capacity. Based on the mathematical formulation we discuss a classical Lagrangian relaxation which allows to decompose the problem into four subproblems, and a new Lagrangian decomposition which decomposes the problem into just a production-inventory subproblem and a routing subproblem. The new decomposition is enhanced with valid inequalities. A computational study is reported to compare the bounds from the two approaches

Algorithm Engineering in Robust Optimization

Robust optimization is a young and emerging field of research having received a considerable increase of interest over the last decade. In this paper, we argue that the the algorithm engineering methodology fits very well to the field of robust optimization and yields a rewarding new perspective on both the current state of research and open research directions. To this end we go through the algorithm engineering cycle of design and analysis of concepts, development and implementation of algorithms, and theoretical and experimental evaluation. We show that many ideas of algorithm engineering have already been applied in publications on robust optimization. Most work on robust optimization is devoted to analysis of the concepts and the development of algorithms, some papers deal with the evaluation of a particular concept in case studies, and work on comparison of concepts just starts. What is still a drawback in many papers on robustness is the missing link to include the results of the experiments again in the design

Combined ship routing and inventory management in the salmon farming industry

We consider a maritime inventory routing problem for Norway's largest salmon farmer both producing the feed at a production factory and being responsible for fish farms located along the Norwegian coast. The company has bought two new ships to transport the feed from the factory to the fish farms and is responsible for the routing and scheduling of the ships. In addition, the company has to ensure that the feed at the production factory as well as at the fish farms is within the inventory limits. A mathematical model of the problem is presented, and this model is reformulated to improve the efficiency of the branch-and-bound algorithm and tightened with valid inequalities. To derive good solutions quickly, several practical aspects of the problem are utilized and two matheuristics developed. Computational results are reported for instances based on the real problem of the salmon farmer

Longitudinal relationship of liver injury with inflammation biomarkers in COVID-19 hospitalized patients using a joint modeling approach

The mechanisms underlying liver disease in patients with COVID-19 are not entirely known. The aim is to investigate, by means of novel statistical techniques, the changes over time in the relationship between inflammation markers and liver damage markers in relation to survival in COVID-19. The study included 221 consecutive patients admitted to the hospital during the first COVID-19 wave in Spain. Generalized additive mixed models were used to investigate the influence of time and inflammation markers on liver damage markers in relation to survival. Joint modeling regression was used to evaluate the temporal correlations between inflammation markers (serum C-reactive protein [CRP], interleukin-6, plasma D-dimer, and blood lymphocyte count) and liver damage markers, after adjusting for age, sex, and therapy. The patients who died showed a significant elevation in serum aspartate transaminase (AST) and alkaline phosphatase levels over time. Conversely, a decrease in serum AST levels was observed in the survivors, who showed a negative correlation between inflammation markers and liver damage markers (CRP with serum AST, alanine transaminase [ALT], and gamma-glutamyl transferase [GGT]; and D-dimer with AST and ALT) after a week of hospitalization. Conversely, most correlations were positive in the patients who died, except lymphocyte count, which was negatively correlated with AST, GGT, and alkaline phosphatase. These correlations were attenuated with age. The patients who died during COVID-19 infection displayed a significant elevation of liver damage markers, which is correlated with inflammation markers over time. These results are consistent with the role of systemic inflammation in liver damage during COVID-19S