• Canada
• Publicationsclose
• 01 natural sciences close
• Natural Sciences and Engineering Research Council of Canada close

Abstract In this paper, we consider a discrete logistic equation x ( n +1)= x ( n ) exp r ( n ) 1 − x ( n ) K ( n ) where {r(n)} and {K(n)} are positive ω-periodic sequences. Sufficient conditions are obtained for the existence of a positive and globally asymptotically stable ω-periodic solution. Counterexamples are given to illustrate that the conclusions in [1] are incorrect.

A dramatic difference in the ability of the reducing An(III) center in AnCp3 (An=U, Np, Pu; Cp=C5 H5 ) to oxo-bind and reduce the uranyl(VI) dication in the complex [(UO2 )(THF)(H2 L)] (L="Pacman" Schiff-base polypyrrolic macrocycle), is found and explained. These are the first selective functionalizations of the uranyl oxo by another actinide cation. At-first contradictory electronic structural data are explained by combining theory and experiment. Complete one-electron transfer from Cp3 U forms the U(IV) -uranyl(V) compound that behaves as a U(V) -localized single molecule magnet below 4 K. The extent of reduction by the Cp3 Np group upon oxo-coordination is much less, with a Np(III) -uranyl(VI) dative bond assigned. Solution NMR and NIR spectroscopy suggest Np(IV) U(V) but single-crystal X-ray diffraction and SQUID magnetometry suggest a Np(III) -U(VI) assignment. DFT-calculated Hirshfeld charge and spin density analyses suggest half an electron has transferred, and these explain the strongly shifted NMR spectra by spin density contributions at the hydrogen nuclei. The Pu(III) -U(VI) interaction is too weak to be observed in THF solvent, in agreement with calculated predictions.

Application of pulsed electric fields (PEFs) is an alternative treatment to thermal pasteurization of liquid foods, which inactivates microorganisms without degrading flavor, texture, and nutrients compared to other conventional technologies. This article scrutinizes the applicability of PEF processing of carbonated beer using a titanium electrode based sealed processing chamber that provides not only effective use of the highest electric field but also eliminates edge effects, and at the same time reduces turbulence by providing steady and uniform flow of the fluid under treatment. The release of metal ions during PEF processing is evaluated by using inductively coupled plasma atomic emission spectrometry (ICP-AES). As metal ions directly affect the organoleptic properties of beer, a sensory evaluation is conducted with the panelists comprised of brewing experts. It has been found that the released amounts of metal ions are lower than the detection levels of ICP-AES, and much lower than what is accepted in consumable foods (<2 parts per billion). Supporting the metal analysis data, the sensory panel also reported nonoff flavors in the PEF-processed beer. The treated and untreated beer samples are aged at 5 °C, 22 °C, and 34 °C for ten days. The shelf-life analysis is conducted for PEF-treated and untreated beer samples. The organoleptic property profile of the beer treated at 4 kV by PEF shows the potential of extending shelf life at least for 90 days. In addition, analytical indicators like the deterioration of trans-iso-α-acids confirm no chemical changes in beer before and after PEF treatment under the conditions studied.

We present a holographic method for computing the response of Rényi entropies in conformal field theories to small shape deformations around a flat (or spherical) entangling surface. Our strategy employs the stress tensor one-point function in a deformed hyperboloid background and relates it to the coefficient in the two-point function of the displacement operator. We obtain explicit numerical results for d = 3 , · · · , 6 spacetime dimensions, and also evaluate analytically the limits where the Rényi index approaches 1 and 0 in general dimensions. We use our results to extend the work of 1602.08493 and disprove a set of conjectures in the literature regarding the relation between the Rényi shape dependence and the conformal weight of the twist operator. We also extend our analysis beyond leading order in derivatives in the bulk theory by studying Gauss-Bonnet gravity.

Different breakup regimes of bubbles and droplets caused by a sudden channel expansion in a microfluidic device are investigated. Without modifying the geometry and by only tuning several dimensionless parameters related to the fluid flow, a microchannel expansion region can produce mono-, bi-, or tri-disperse bubble or droplet populations.

In homogenous solution, cholesterol autoxidation leads to a mixture of epimers of 5 primary products, whose concentrations vary in the presence/absence of antioxidants, such as vitamin E. Two of the products (5α-OOH and 6β-OOH) undergo Hock fragmentation to yield electrophilic secosterols implicated in disease. Herein, we show that the product distribution is similar in phospholipid bilayers, in that the 7-OOHs are the major products, but the presence/absence of vitamin E has no effect on the distribution. Cholesterol 7α-OOH, but not 7β-OOH, undergoes Hock fragmentation to yield a mixture of unprecedented A-ring cleavage products and 6,7-epoxides. When subjected to typical derivatization conditions, 7α-OOH yields products with essentially indistinguishable chromatographic and spectroscopic features from the previously identified secosterols, casting further doubt on their controversial origin from endogenous O3 .

Critical transitions in ecosystem states are often sudden and unpredictable. Consequently, there is a concerted effort to identify measurable early warning signals (EWS) for these important events. Aquatic ecosystems provide an opportunity to observe critical transitions due to their high sensitivity and rapid response times. Using palaeoecological techniques, we can measure properties of time series data to determine if critical transitions are preceded by any measurable ecosystem metrics, that is, identify EWS. Using a suite of palaeoenvironmental data spanning the last 2,400 years (diatoms, pollen, geochemistry, and charcoal influx), we assess whether a critical transition in diatom community structure was preceded by measurable EWS. Lake Vera, in the temperate rain forest of western Tasmania, Australia, has a diatom community dominated by Discostella stelligera and undergoes an abrupt compositional shift at ca. 820 cal yr BP that is concomitant with increased fire disturbance of the local vegetation. This shift is manifest as a transition from less oligotrophic acidic diatom flora (Achnanthidium minutissimum, Brachysira styriaca, and Fragilaria capucina) to more oligotrophic acidic taxa (Frustulia elongatissima, Eunotia diodon, and Gomphonema multiforme). We observe a marked increase in compositional variance and rate-of-change prior to this critical transition, revealing these metrics are useful EWS in this system. Interestingly, vegetation remains complacent to fire disturbance until after the shift in the diatom community. Disturbance taxa invade and the vegetation system experiences an increase in both compositional variance and rate-of-change. These trends imply an approaching critical transition in the vegetation and the probable collapse of the local rain forest system.

Abstract Solid solution hardening is one of common methods to increase hardness of metals by adding solute atoms. The mechanism for solution hardening is ascribed to the differences in atomic size and elastic modulus between the host and the solute. However, the theory is somehow ambiguous without clear clues for optimizing the balance between the two effects towards maximized hardening effectiveness. Current selection of alloying elements for solution hardening is largely based on experience. In this study, we re-examine the conventional mechanism and propose a single-parameter model using electron work function (EWF) as an indicator to evaluate the capability of solute atoms in solid solution hardening. With relevant experiments, we demonstrate the correlation between electron work function and solution hardening effectiveness. The prediction from the proposed EWF model is consistent with the experimental observations.

AbstractIn this paper, we study the expressive power and the complexity of first-order logic with arithmetic, as a query language over relational and constraint databases. We consider constraints over various domains (N, Z, Q, and R), and with various arithmetical operations (⩽, +, ×, etc.).We first consider the data complexity of first-order queries. We prove in particular that linear queries can be evaluated in AC0 over finite integer databases, and in NC1 over linear constraint databases. This improves previously known bounds. We also show that over all domains, enough arithmetic lead to arithmetical queries, therefore, showing the frontiers of constraints for database purposes.We then tackle the problem of the expressive power, with the definability of the parity and the connectivity, which are the most classical examples of queries not expressible in first-order logic over finite structures. We prove that these two queries are first-order definable in the presence of (enough) arithmetic. Nevertheless, we show that they are not definable with constraints of interest for constraint databases such as linear constraints for instance. Finally, we developed reduction techniques for queries over constraint databases, that allow us to draw conclusions with respect to their undefinability in various constraint query languages.

Novel devices based on the use of dielectric elastomer actuators (DEA) have been proposed for a large variety of different applications. In many of these applications, DEAs are envisioned to be in direct or close proximity to the human body. Since DEAs usually require high voltage for their actuation, the safety of individuals operating or using these devices should be ensured. In this paper, safety standards based on safe limits for electrical discharge are investigated. Flat and cylindrical DEA configurations, which are generally considered as the building blocks for the design of DEA-based systems, are investigated in detail. Relevant elements and factors that affect the electrical discharge of DEA devices are analyzed and guidelines to design DEA-based devices that are not of harm for humans are provided. The performed analyses are experimentally validated using flat DEA samples. The safety requirements that should be considered when wrapping DEAs around the body (specifically the legs) are also briefly investigated to provide a practical example of interest for the biomedical community.