Determination of trace metals in estuarine sediments by graphite-furnace atomic absorption spectrometry

A simple and rapid acid digestion method for the decomposition of estuarine sediments is described. Quantitative recovery of Cd, Pb, Cu, Ni, Co, Be and Co is demonstrated. Sensitive, precise and accurate determination of these trace metals by graphite-furnace atomic absorption spectrometry in combination with the L'vov Platform provides an interference-free technique that permits calibration with simple aqueous solutions of metal standards. The accuracy of the method has been confirmed by analysis of two marine sediment reference materials, MESS-1 and BCSS-1.     

Synthesis of 15N-enriched pseudouridine derivatives

[reaction: see text]. A procedure for the chemical synthesis of [3-15N]-labeled pseudouridine and a methylated derivative was developed. A suitably protected pseudouridine precursor was nitrated at N3 followed by treatment with 15NH4Cl to afford the 15N-labeled product in six steps with a 20% yield. This methodology will allow for the production of RNAs with [3-15N]pseudouridine and [3-15N-methyl]pseudouridine at specific locations.     

Synthesis of helix 69 of Escherichia coli 23S rRNA containing its natural modified nucleosides,m(3)Psi and Psi

The synthesis of 3-methylpseudouridine (m(3)Psi) phosphoramidite, 5'-O-[benzhydryloxybis(trimethylsilyloxy)silyl]-2'-O-[bis(2-acetoxyethoxy)methyl]-3-methylpseudouridine-3'-(methyl-N,N-diisopropyl)phosphoramidite, is reported. Selective pivaloyloxymethyl protection of the Psi N1 followed by methylation at N3 was used to generate the naturally occurring pseudouridine analogue. The m(3)Psi phosphoramidite was used in combination with pseudouridine (Psi) and standard base phosphoramidites to synthesize a 19-nucleotide RNA representing helix 69 of Escherichia coli 23S ribosomal RNA (rRNA) (residues 1906-1924), containing a single m(3)Psi at position 1915 and two Psi's at positions 1911 and 1917. Our synthesis of the fully modified helix 69 RNA demonstrates the ability to make milligram quantities of RNA that can be used for further high-resolution structure studies. Site-selective introduction of the methyl group at the N3 position of pseudouridine at position 1915 causes a slight increase in the thermodynamic stability of the RNA hairpin relative to pseudouridine; RNAs containing either uridine or 3-methyluridine at position 1915 have similar stability. One-dimensional imino proton NMR and circular dichroism spectra of the modified RNAs reveal that the methyl group does not cause any substantial changes in the RNA hairpin structure.     

A branch-and-price algorithm for the Vehicle Routing Problem with Deliveries,Selective Pickups and Time Windows

In the Vehicle Routing Problem with Deliveries, Selective Pickups and Time Windows, the set of customers is the union of delivery customers and pickup customers. A fleet of identical capacitated vehicles based at the depot must perform all deliveries and profitable pickups while respecting time windows. The objective is to minimize routing costs, minus the revenue associated with the pickups. Five variants of the problem are considered according to the order imposed on deliveries and pickups. An exact branch-and-price algorithm is developed for the problem. Computational results are reported for instances containing up to 100 customers.     

Synthesis and properties of oligonucleotides that contain a triazole‐linked nucleic acid dimer

New chemically modified oligonucleotides at the site of the backbone are needed to improve the properties of oligonucleotides. A practical synthesis for a triazole‐linked nucleoside dimer based on a PNA‐like structure has been developed. This involves synthesizing two uracil‐based monomers that contain either an azide or an alkyne functionality, followed by copper‐catalyzed 1,3‐dipolar cycloaddition. This dimer was incorporated within an oligonucleotide via phosphoramidite chemistry and UV‐monitored thermal denaturation data illustrates slight destabilization relative to its target complementary sequence. This chemically modified dimer will allow for a future investigation of its properties within DNA and RNA‐based applications. J. Heterocyclic Chem., (2011).     

Column generation for vehicle routing problems with multiple synchronization constraints

Synchronization of workers and vehicles plays a major role in many industries such as logistics, healthcare or airport ground handling. In this paper, we focus on operational ground handling planning and model it as an archetype of vehicle routing problems with multiple synchronization constraints, coined as “abstract vehicle routing problem with worker and vehicle synchronization” (AVRPWVS). The AVRPWVS deals with routing workers to ground handling jobs such as unloading baggage or refuelling an aircraft, while meeting each job’s time window. Moreover, each job can be performed by a variable number of workers. As airports span vast distances and due to security regulations, workers use vehicles to travel between locations. Furthermore, each vehicle, moved by a driver, can carry several workers. We propose two mathematical multi-commodity flow formulations based on time-space networks to efficiently model five synchronization types including movement and load synchronization. Moreover, we develop a branch-and-price heuristic that employs both conventional variable branching and a novel variable fixing strategy. We demonstrate that the procedure achieves results close to the optimal solution in short time when compared to the two integer models.     

Multi-phase dynamic constraint aggregation for set partitioning type problems

Dynamic constraint aggregation is an iterative method that was recently introduced to speed up the linear relaxation solution process of set partitioning type problems. This speed up is mostly due to the use, at each iteration, of an aggregated problem defined by aggregating disjoint subsets of constraints from the set partitioning model. This aggregation is updated when needed to ensure the exactness of the overall approach. In this paper, we propose a new version of this method, called the multi-phase dynamic constraint aggregation method, which essentially adds to the original method a partial pricing strategy that involves multiple phases. This strategy helps keeping the size of the aggregated problem as small as possible, yielding a faster average computation time per iteration and fewer iterations. We also establish theoretical results that provide some insights explaining the success of the proposed method. Tests on the linear relaxation of simultaneous bus and driver scheduling problems involving up to 2,000 set partitioning constraints show that the partial pricing strategy speeds up the original method by an average factor of 4.5.     

Restoration of atmospherically degraded images using complex spectral ratios

A method for reconstructing atmospherically degraded stellar images from measured spectral ratios is described. An advantage of the ratio method is that an auxillary measurement to establish the OTF of the atmosphere is not required in most cases of interest.