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.     

2,2']paracyclophane-based π-conjugated molecular wires reveal molecular-junction behavior

The electronic coupling as well as the attenuation factor (β), which depends primarily on the nature of the molecular bridge and is used as a benchmark to test the molecular wire behavior, have been determined in a systematic study carried out on a series of ZnP/C(60) conjugates connected through a [2,2']paracyclophane-oligophenylenevinylene (pCp-oPPV). The convergent synthesis involves a series of Horner-Emmons olefination reactions or double palladium-catalized Heck-type reactions. ZnP-pCp-C(60) conjugates were finally obtained by the 1,3-dipolar cycloaddition reaction of the in situ-generated azomethyne ylide containing the ZnP-pCp moiety to the [60]fullerene using Prato conditions. Experimental (UV-vis, fluorescence, transient absorption spectroscopy, and solution electrochemistry) and theoretical studies revealed that the pCps act as molecular junctions. If hole transfer is assumed to be the dominant charge transfer (CT) mechanism, CT is facilitated in one direction (from C(60) to ZnP via pCp) but disfavored in the other direction (from ZnP to C(60) via pCp).     

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.     

A new approach based on a combination of direct and headspace cold-fiber solid-phase microextraction modes in the same procedure for the determination of polycyclic aromatic hydrocarbons and phthalate esters in soil samples

This study describes a new approach to cold-fiber solid-phase microextraction (CF-SPME) based on a combination of different extraction modes in the same extraction procedure. Also, the high quantity of water required to facilitate both the desorption of analytes from the matrix and their transport to the fiber coating is reported. The extraction mode was changed from the direct to the headspace mode in a single extraction while manipulating the extraction times and coating temperature to improve the extraction of compounds with different volatilities. Compounds with low volatility were better extracted in the direct mode, while the headspace mode was more appropriate for volatile compounds. Polycyclic aromatic hydrocarbons (PAHs) and phthalic acid esters (PEs) in sand or soil samples were used as model compounds and matrices in this study. The optimized conditions were: sample pH in the range of 4-7, addition of 12 mL of 194 g L(-1) aqueous NaCl solution in a 15 mL vial, and 80 min total extraction time with a sample temperature of 90°C (50 min in direct mode with coating at 90°C followed by 30 min in headspace mode with coating at 30°C). The proposed procedure was compared with conventional CF-SPME (with and without addition of water) and was found to be more effective for all the analytes, since it is capable of extracting both heavier and lighter compounds from soil samples in a single extraction procedure. The use of an excess of water and a combination of extraction modes in the same CF-SPME procedure are the main factors responsible for this enhancement. The proposed method was applied to the extraction of PAHs and PEs in spiked soil samples and excellent results were obtained for most of the compounds evaluated.     

Alcohol and metal determination in alcoholic beverages through high-temperature liquid-chromatography coupled to an inductively coupled plasma atomic emission spectrometer

In the present work, an inductively coupled plasma atomic emission spectrometry (ICP-AES) system was used as a high temperature liquid chromatography (HTLC) detector for the determination of alcohols and metals in beverages. For the sake of comparison, a refractive index (RI) detector was also employed for the first time to detect alcohols with HTLC. The organic compounds studied were methanol, ethanol, propan-1-ol and butan-1-ol (in the 10-125 mg/L concentration range) and the elements tested were magnesium, aluminum, copper, manganese and barium at concentrations included between roughly 0.01 and 80 mg/L. Column heating temperatures ranged from 80 to 175 °C and the optimum ones in terms of peak resolution, sensitivity and column lifetime were 125 and 100 °C for the HTLC-RI and HTLC-ICP-AES couplings, respectively. The HTLC-ICP-AES interface design (i.e., spray chamber design and nebulizer type used) was studied and it was found that a single pass spray chamber provided about 2 times higher sensitivities than a cyclonic conventional design. Comparatively speaking, limits of detection for alcohols were of the same order for the two evaluated detection systems (from 5 to 25 mg/L). In contrast, unlike RI, ICP-AES provided information about the content of both organic and inorganic species. Furthermore, temperature programming was applied to shorten the analysis time and it was verified that ICP-AES was less sensitive to temperature changes and modifications in the analyte chemical nature than the RI detector. Both detectors were successfully applied to the determination of short chain alcohols in several beverages such as muscatel, pacharan, punch, vermouth and two different brands of whiskeys (from 10 to 40 g of ethanol/100 g of sample). The results of the inorganic elements studied by HTLC-ICP-AES were compared with those obtained using inductively coupled plasma mass spectrometry (ICP-MS) obtaining good agreement between them. Recoveries found for spiked samples were close to 100% for both, inorganic elements (with both HLTC-ICP-AES and ICP-MS) and alcohols (with both HTLC-ICP-AES and HTLC-RI hyphenations).