Eutrophication risk assessment in Hamilton Harbour: System analysis and evaluation of nutrient loading scenarios

Environmental modeling has been an indispensable tool of the Hamilton Harbour restoration efforts, where a variety of data-oriented and process-based models have been used for linking management actions with potential ecosystem responses. In this study, our objective is to develop a biogeochemical model that can effectively describe the interplay among the different ecological mechanisms modulating the eutrophication problems in Hamilton Harbour, Ontario, Canada. First, we provide the rationale for the model structure adopted, the simplifications included, and the formulations used during the development phase of the model. We then present the results of a calibration exercise and examine the ability of the model to sufficiently reproduce the average observed patterns along with the major cause–effect relationships underlying the Harbour water quality conditions. The present modeling study also undertakes an estimation of the critical nutrient loads in the Harbour based on acceptable probabilities of compliance with different water quality criteria (e.g., chlorophyll a, total phosphorus). Our model suggests that the water quality goals for TP (17 μg L⁻¹) and chlorophyll a concentrations (5–10 μg L⁻¹) will likely be met, if the Hamilton Harbour RAP phosphorus loading target at the level of 142 kg day⁻¹ is achieved. We also provide evidence that the anticipated structural shifts of the zooplankton community will determine the restoration rate as well as the stability of the new trophic state in the Harbour.     

Electronic structures of neutral, cationic and dicationic states of the low band gap polymers. Polythieno[3,4-b]benzene, a case study

The electronic structures of neutral cationic and dicationic states of oligothieno[3,4-b]benzene containing up to 20 repeating units have been studied using broken symmetry B3LYP/3-21G* method. The model predicts that short oligomers (up to decamers) have closed shell aromatic ground state, while the ground state of longer oligomers possesses multireference character and cannot be described within a framework of one determinant methods. It has been found that the ground state has significant contributions from triplet state. The S0 → S1 energy calculated for longest of polythieno[3,4-b]benzene (PITN) oligomer containing 20 repeating units is in excellent agreement with experiment. Unlike polythiophene where the ground state of dications is open shell polaron pair state dicationic ground state of calculated oligomers is closed shell bipolaronic state (at least up to oligomers containing 20 repeating units) which was confirmed by stability calculations.     

Simple scanner-based image analysis for corrosion testing: Concrete application

A methodology for the assessment of the crown corrosion in concrete sewer pipes was developed based upon the principle that the surface roughness increases when concrete corrodes. The roughness was quantified by correlating the depths of the surface pits to the lengths of shadows produced in a single source of incident light. A computer program was used to reconstruct a pseudo three-dimensional concrete exterior and obtain the averaged corrosion rate.     

Experimental Characterization of an Electrohydrodynamic Micropump for Cryogenic Spot Cooling Applications

This article presents a study on the characterization of a planar, multistage, electrohydrodynamic (EHD) ion-drag micropump for pumping of liquid nitrogen. Two designs of the pump, consisting of different emitter configurations (flat and saw-tooth), similar emitter-collector spacing (50 microns), and similar gaps between successive electrode pairs (100 microns), were tested at DC voltages ranging from 0 to 2.5 kV. The electric currents they generated and the corresponding static pressure heads were measured to characterize the pumping performance. Pressure and current onset voltages as well as pressure-voltage (P-V) and pressure-current (P-I) relationships were investigated. The highest pressure head (30 Pa at 1700 V) was generated with the saw-tooth design. After collecting and processing the data for various prototypes, it was evident that incorporating saw-tooth electrodes can significantly improve the performance of the micropump.     

Cellular automata simulation of the phenomenon of multiple crystallization

The phenomenon of multiple crystallization from supersaturated solutions was simulated. For this simulation the model used is based on partitioning cellular automata (CA) with probabilistic table lookup for the implementation of diffusion and interaction according to diffusion and crystal growth basic equations. Such an approach, which takes into account temperature, crystallographic indexes of crystal surface and local fluctuations describes the problem at a mesoscopic level. This simulates the physical processes of diffusion, nucleation, and aggregation of particles. Results were obtained that are in qualitative agreement with the behavior of the majority of real situation for the: (i) temperature dependence of the crystal solubility; (ii) temperature dependence of the concentration of beginning of crystallization from supersaturated solutions. It was also studied the processes of crystallization at different temperatures and analyzed the behavior of the different parameters involved in crystallization systems: concentration of solution, interfacial energy, mass of crystals and average size of crystal. Finally, the process of crystallization was modeled at several conditions of temperature gradient.     

Single-molecule avidin-biotin association reaction studied by force-clamp spectroscopy

Using single-molecule force-clamp spectroscopy, where the distance between the AFM tip and the sample surface is fixed and a few parallel avidin-biotin complexes are kept stretched by a certain force, we were able to observe the formation of single avidin-biotin bonds. Perspectives to use such an approach to study association reactions at single-molecule level in the conditions resembling those characteristic for some processes in vivo (e.g. virus-cell membrane attachment) are briefly discussed.     

Low-swelling proton-conducting copoly(aryl ether nitrile)s containing naphthalene structure with sulfonic acid groups meta to the ether linkage

Wholly aromatic poly(aryl ether ether nitrile)s containing naphthalene structure with sulfonic acid groups meta to ether linkage (m-SPAEEN), intended for fuel cells applications as proton conducting membrane materials, were prepared via nucleophilic substitution polycondensation reactions. The incorporation of rigid naphthalene structure with meta-sulfonic acid groups was with the intent of improving the aggregation of hydrophilic and hydrophobic domains and to increase the acidity and conductivities. m-SPAEEN copolymers were readily synthesized by potassium carbonate mediated nucleophilic polycondensation reactions of commercially available monomers: 2,6-difluorobenzonitrile (2,6-DFBN), 2,8-dihydroxynaphthalene-6-sulfonate sodium salt (2,8-DHNS-6), and 4,4′-biphenol (4,4′-BP) in dimethylsulfoxide (DMSO) at 160-170 °C. The sulfonic acid group content (SC), expressed as a number per repeat unit of polymer, ranged from 0 to 0.6 and was readily controlled by changing the feed ratio of 2,8-DHNS-6 to 2,6-DFBN. High thermal stability of m-SPAEEN copolymers was indicated by observed glass transition temperatures (T_gs) ranging from 223 to 335 °C in sodium salt form and from 230 to 260 °C in acid form (m-SPAEENH) and decomposition temperatures (T_d)s over 250 °C in acid form and over 350 °C in sodium form in both nitrogen and air. All m-SPAEENH copolymers exhibited reasonable flexibility and tensile strength in the range of 39-78 MPa, indicating they were mechanically stronger than Nafion^®117, which had an approximate value of 10 MPa under the same test conditions. As expected, m-SPAEENH copolymers showed considerably reduced moisture absorption compared to previously prepared sulfonated hydroquinone based poly(aryl ether nitrile). m-SPAEENH copolymers also showed improved proton conductivities. Proton conductivity curves parallel to that of Nafion 117 were obtained with proton conductivity of 10⁻¹ S/cm at equivalent ion exchange capacities (IEC) of 1.6 and 1.9, comparable to Nafion^®117. The best compromise combining PEM mechanical strength, water swelling and proton conductivity, was achieved at SC of 0.5 and 0.6.     

Inventory competition and incentives to back-order

In this paper we consider the issue of inventory control in a multi-period environment with competition on product availability. Specifically, when a product is out of stock, the customer often must choose between placing a back-order or turning to a competitor selling a similar product. We consider a competition in which customers may switch between two retailers (substitute) in the case of a stock-out at the retailer of their first choice. In a multi-period setting, the following four situations may arise if the product is out of stock: (i) sales may be lost; (ii) customers may back-order the product with their first-choice retailer; (iii) customers may back-order the product with their second-choice retailer; or (iv) customers may attempt to acquire the product according to some other more complex rule. The question we address is: how do the equilibrium stocking quantities and profits of the retailers depend on the customers' back-ordering behaviors? In this work we consider the four alternative back-ordering scenarios and formulate each problem as a stochastic multi-period game. Under appropriate conditions, we show that a stationary base-stock inventory policy is a Nash equilibrium of the game that can be found by considering an appropriate static game. We derive conditions for the existence and uniqueness of such a policy and conduct a comparative statics analysis. Analytical expressions for the optimality conditions facilitate managerial insights into the effects of various back-ordering mechanisms. Furthermore, we recognize that often a retailer is willing to offer a monetary incentive to induce a customer to back-order instead of going to the competitor. Therefore, it is necessary to coordinate incentive decisions with operational decisions about inventory control. We analyze the impact of incentives to back-order the product on the optimal stocking policies under competition and determine the conditions that guarantee monotonicity of the equilibrium inventory in the amount of the incentive offered. Our analysis also suggests that, counterintuitively, companies might benefit from making their inventories “visible” to competitors' customers, since doing so reduces the level of competition, decreases optimal inventories and simultaneously increases profits for both players.     

Taking Perturbation to the Accuracy Frontier: A Hybrid of Local and Global Solutions

Local (perturbation) methods compute solutions in one point and tend to deliver far lower accuracy levels than global solution methods. We develop a hybrid method that solves for some policy functions locally (using a perturbation method) and that solves for the other policy functions globally (using closed-form expressions and a numerical solver). We applied our hybrid method to solve large-scale RBC models used in the comparison analysis of Kollmann et al. (J Econ Dyn Control 35:186–202, 2011b). We obtain more accurate solutions than those produced by any other (either local or global) solution method participating in that comparison. Our running time is a few seconds.     

Ferroelectricity in synthetic metals: Reality and hypotheses

Ferroelectricity is one of the demanded effects in fundamental and applied solid state physics. Till now, the ferroelectrics were available mostly in the inorganic world. The breakthrough of 2000s was an unexpected discovery of the ferroelectricity related to the charge ordering in quasi-1D organic conductors (TMTTF)₂X, and in some layered compounds. The achieved understanding of underlying mechanisms allows to speculate on synthesis of a would-be ferroelectric polymer: it must possess a combination of dimerizations of sites and bonds, one of which must be build-in and another spontaneous. The theory of these “combined Peierls states” predicts an existence of solitons (dimerization kinks) with non-integer variable charges—they are the walls separating domains with opposite electric polarization. The physics of these exotic solitons will serve to describe transient processes in ferroelectric polymers, linking optical- and low-frequency properties. The promising example of such an (AB)_x conjugated polymer has already appeared but was not yet tested for ferroelectricity. A wide chemical search is necessary because of a problematic competition of an anti-ferroelectric phase, whose occurrence depends on complicated details of the interchain coupling.