Spatial Lanchester models

Lanchester equations have been widely used to model combat for many years, nevertheless, one of their most important limitations has been their failure to model the spatial dimension of the problems. Despite the fact that some efforts have been made in order to overcome this drawback, mainly through the use of Reaction–Diffusion equations, there is not yet a consistently clear theoretical framework linking Lanchester equations with these physical systems, apart from similarity. In this paper, a spatial modeling of Lanchester equations is conceptualized on the basis of explicit movement dynamics and balance of forces, ensuring stability and theoretical consistency with the original model. This formulation allows a better understanding and interpretation of the problem, thus improving the current treatment, modeling and comprehension of warfare applications. Finally, as a numerical illustration, a new spatial model of responsive movement is developed, confirming that location influences the results of modeling attrition conflict between two opposite forces.     

Hysteresis effects under CIR interest rates

Most decision making research in real options focuses on revenue uncertainty assuming discount rates remain constant. However, for many decisions revenue or cost streams are relatively static and investment is driven by interest rate uncertainty, for example the decision to invest in durable machinery and equipment. Using interest rate models from Cox et al. (1985b), we generalize the work of Ingersoll and Ross (1992) in two ways. Firstly, we include real options on perpetuities (in addition to zero coupon cash flows). Secondly, we incorporate abandonment or disinvestment as well as investment options, and thus model interest rate hysteresis (parallel to revenue uncertainty in Dixit (1989a)). Under stochastic interest rates, economic hysteresis is found to be significant, even for small sunk costs.     

A combinatorial proof of Marstrand’s theorem for products of regular Cantor sets

In a paper from 1954 Marstrand proved that if K⊂R² has a Hausdorff dimension greater than 1, then its one-dimensional projection has a positive Lebesgue measure for almost all directions. In this article, we give a combinatorial proof of this theorem when K is the product of regular Cantor sets of class C^1+α, α>0, for which the sum of their Hausdorff dimension is greater than 1.     

Solving the vendor–buyer integrated inventory system with arithmetic–geometric inequality

In the past, economic order quantity (EOQ) and economic production quantity (EPQ) were treated independently from the viewpoints of the buyer or the vendor. In most cases, the optimal solution for one player was non-optimal to the other player. In today’s competitive markets, close cooperation between the vendor and the buyer is necessary to reduce the joint inventory cost and the response time of the vendor–buyer system. The successful experiences of National Semiconductor, Wal-Mart, and Procter and Gamble have demonstrated that integrating the supply chain has significantly influenced the company’s performance and market share (Simchi-Levi et al. (2000) [1]). Recently, Yang et al. (2007) [2] presented an inventory model to determine the economic lot size for both the vendor and buyer, and the number of deliveries in an integrated two stage supply chain. In this paper, we present an alternative approach to determine the global optimal inventory policy for the vendor–buyer integrated system using arithmetic–geometric inequality.     

Generalized Benders’ Decomposition for topology optimization problems

This article considers the non-linear mixed 0–1 optimization problems that appear in topology optimization of load carrying structures. The main objective is to present a Generalized Benders’ Decomposition (GBD) method for solving single and multiple load minimum compliance (maximum stiffness) problems with discrete design variables to global optimality. We present the theoretical aspects of the method, including a proof of finite convergence and conditions for obtaining global optimal solutions. The method is also linked to, and compared with, an Outer-Approximation approach and a mixed 0–1 semi definite programming formulation of the considered problem. Several ways to accelerate the method are suggested and an implementation is described. Finally, a set of truss topology optimization problems are numerically solved to global optimality.     

Mechanism of formation of the internal aldimine in pyridoxal 5'-phosphate-dependent enzymes

In this paper we studied the mechanism of formation of the internal aldimine, a common intermediate to most pyridoxal 5'-phosphate (PLP)-dependent enzymes. A large model based on the crystal structure from the human ornithine decarboxylase (ODC) enzyme was constructed and in total accounts for 504 atoms. The reaction mechanism was investigated using the ONIOM methodology (B3LYP/6-31G(d)//AM1), and the final energies were calculated with the M06/6-311++G(2d,2p)//B3LYP/6-31G(d) level of theory. It was demonstrated that the reaction is accomplished in three sequential steps: (i) the nucleophilic attack of Lysine69 to PLP, (ii) the carbinolamine formation, and (iii) a final dehydration step. For the carbinolamine formation, several mechanistic hypotheses were explored, and the preferred pathway assigns a key role for the conserved active site Cys360. The overall reaction is exergonic in -9.1 kcal/mol, and the rate-limiting step is the dehydration step (E(a) = 13.5 kcal/mol). For the first time, we provide an atomistic portrait of this mechanism in an enzymatic environment. Moreover, we were able to assign a novel role to Cys360 in the ODC reaction mechanism that was never proposed.     

Highly efficient hydrogen-bonding catalysis of the Diels-Alder reaction of 3-vinylindoles and methyleneindolinones provides carbazolespirooxindole skeletons

Carbazolespirooxindole derivatives were synthesized in a high-yielding, atypically rapid, stereocontrolled Diels-Alder reaction catalyzed by a C(2)-symmetric bisthiourea organocatalyst. Simple precursors and mild conditions were used to construct carbazolespirooxindole derivatives with high enantiopurity and structural diversity under H-bonding catalysis. The practical approach recycles the organocatalyst and solvent. This simple and efficient operational procedure will allow diversity-oriented syntheses of this intriguing class of compounds.     

Highly polar carbohydrates stack onto DNA duplexes via CH/π interactions

Carbohydrate-nucleic acid contacts are known to be a fundamental part of some drug-DNA recognition processes. Most of these interactions occur through the minor groove of DNA, such as in the calicheamicin or anthracycline families, or through both minor and major groove binders such as in the pluramycins. Here, we demonstrate that carbohydrate-DNA interactions are also possible through sugar capping of a DNA double helix. Highly polar mono- and disaccharides are capable of CH/π stacking onto the terminal DNA base pair of a duplex as shown by NMR spectroscopy. The energetics of the carbohydrate-DNA interactions vary depending on the stereochemistry, polarity, and contact surface of the sugar involved and also on the terminal base pair. These results reveal carbohydrate-DNA base stacking as a potential recognition motif to be used in drug design, supramolecular chemistry, or biobased nanomaterials.     

Tuning the gas sensing performance of single PEDOT nanowire devices

This paper reports the synthesis and dopant dependent electrical and sensing properties of single poly(ethylenedioxythiophene) (PEDOT) nanowire sensors. Dopant type (i.e. polystyrenesulfonate (PSS(-)) and perchlorate (ClO(4)(-))) and solvent (i.e. acetonitrile and 1 : 1 water-acetonitrile mixture) were adjusted to change the conjugation length and hydrophilicity of nanowires which resulted in change of the electrical properties and sensing performance. Temperature dependent coefficient of resistance (TCR) indicated that the electrical properties are greatly dependent on dopants and electrolyte where greater disorder was found in PSS(-) doped PEDOT nanowires compared to ClO(4)(-) doped nanowires. Upon exposure to different analytes including water vapor and volatile organic compounds, these nanowire devices displayed substantially different sensing characteristics. ClO(4)(-) doped PEDOT nanowires from an acetonitrile bath show superior sensing responses toward less electronegative analytes and followed a power law dependence on the analyte concentration at high partial pressures. These tunable sensing properties were attributed to variation in the conjugation lengths, dopant type and concentration of the wires which may be attributed to two distinct sensing mechanisms: swelling within the bulk of the nanowire and work function modulation of Schottky barrier junction between nanowire and electrodes.     

Ionic azo-codendrimers: Influence of the acids contents in the liquid crystalline properties and the photoinduced optical anisotropy

A series of codendrimers has been prepared by the grafting of poly(propylene imine) PPI-(NH₂)₁₆ (G = 3) with two different carboxylic acids: the aromatic-based 5-[4′-(4-cyanophenylazo)phenyloxy]pentanoic acid (AZO) and the aliphatic 2,2-bis(undecanoyloxymethylene)propionic acid (BUPA) in different proportions. Their thermal properties, liquid crystalline behavior and photoinduced optical anisotropy have been investigated. The formation of the ionic compounds was confirmed by nuclear magnetic resonance (NMR) spectroscopy, and Fourier transform infrared (FT-IR) spectroscopy. The influence of the acid percentage in the liquid crystalline behavior was investigated by means of differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and X-ray diffractometry (XRD). All the resulting co-dendrimers present liquid crystalline properties displaying an evolution from nematic mesophase for the azo-richer dendrimers to smectic A mesophase for the BUPA-richer dendrimers. Only materials with low azobenzene contents up to four AZO units per dendrimer on average were processable by casting from dichloromethane solutions and resulted in transparent thin films appropriate for optical studies. The photoinduced dichroism reached was higher in the dendrimer with higher azo content (four units per dendrimer) being this material a good compromise between processability and optical response.