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The kinetics and mechanism of the stepwise cis-trans isomerization reactions of all-trans-β-carotene dissolved in MCT (medium-chain triglyceride) oil at temperatures in the range of 80-160 °C have been analyzed using multiresponse modeling. Quantitation of the cis-isomers was performed using HPLC-DAD and quantitation at the reaction isosbestic point at 421 nm. Multiresponse kinetic modeling using the Bayesian criterion was initially performed at 120 °C to determine the best model. Subsequently, the reparametrized Arrhenius equation was used to calculate the activation energies of all reactions. The equilibrium constants for the individual isomerization reactions were determined from the rate constants and the final product distributions. The enthalpies and entropies of the isomerization reactions were determined from the temperature dependence of the equilibrium constants. The 13-cis and 13,13'-di-cis isomers were found to be the fastest formed isomers followed by the 9-cis, 9,13-di-cis, and 13,15-di-cis isomers, where the latter was found to be formed from 13-cis and not the 15-cis isomer. The relative free energies of the β-carotene isomers were determined as all-trans < 13-cis < 9-cis < 13,13'-di-cis < 9,13-di-cis ≈ 15-cis < 13,15-di-cis. The entropic contribution of each reaction was found to play an important role in the ordering. It is concluded that the β-carotene system is quite labile at temperatures ranging from 80 to 160 °C and resulting in equilibrium distributions of the cis-trans isomers.

Solid lipid nanoparticles (SLNs) containing up to 37.5 wt % all-trans β-carotene in the lipid phase are potential water-dispersible food colorants. SLNs have been made by hot-melt high-pressure homogenization with fully hydrogenated sunflower oil and with polysorbate 80 and sunflower lecithin as stabilizers. Atomic force microscopy revealed the SLNs had thin platelet structures most likely derived from the triglyceride crystal β-form, as detected by X-ray diffraction. No indications of crystalline β-carotene were detected. High-performance liquid chromatography analysis showed the extensive isomerization of β-carotene into more than 10 cis isomers, suggesting that it is present as an amorphous mixture. The high β-carotene loadings did not affect the triglyceride crystal structure and the morphology of the SLNs. It is suggested the SLNs consist of a platelet core of crystalline triglyceride surrounded by an amorphous β-carotene-containing layer. The layered structure is suggested to affect the coloring power of the SLNs at β-carotene loadings above 15 wt % of the lipid phase.

In this study we demonstrate how the notion of diversification can be used in broad-scale resource allocation for surveillance of invasive species. We consider the problem of short-term surveillance for an invasive species in a geographical environment. We find the optimal allocation of surveillance resources among multiple geographical subdivisions via application of a classical portfolio framework, which allocates investments among multiple financial asset types with uncertain returns in a portfolio that maximizes the performance and, by meeting the desired diversification targets, protects against errors in estimating the portfolio's performance. We illustrate the approach with a case study that applies a spatial transmission model to assess the risk of spread of the emerald ash borer (EAB), a significant pest in North America, with infested firewood that may be carried by visitors to campground facilities in central Canada. Adding the diversification objective yields an expected survey performance that is comparable with undiversified optimal allocation, but more importantly, makes the geographical distribution of survey priorities less subject to possible errors in the spread rate estimates. Overall, diversification of pest surveillance can be viewed as a viable short-term strategy for hedging against uncertainty in expert- and model-based assessments of pest invasion risk.

The highly hydrophobic β‐carotene is often distributed or dissolved in triglycerides to enhance either nutritional or coloring effects. This study aims at elucidating the physical state of β‐carotene that at high concentrations are mixed into a solid high‐melting tri‐glyceride matrix by dissolution at high temperatures (165 °C) in the melted triglyceride. Extensive isomerization of β‐carotene is observed by HPLC after melting crystalline all‐trans β‐carotene and in the solid mixtures of β‐carotene and fully hydrogenated sunflower oil. Crystalline triglyceride is found in the mixed samples by XRPD analysis whereas no signs of crystalline lattice structures of β‐carotene are detected. DSC thermograms show only the melting and recrystallization events of triglycerides, which are affected by the presence of β‐carotene. Severe line broadening is observed in the ¹³C CP/MAS NMR spectra of the β‐carotene‐triglyceride mixtures when compared to crystalline β‐carotene, demonstrating the lack of long‐range order of the carotene. Altogether, the results demonstrate that β‐carotene is present as an amorphous mixture of trans‐ and cis‐isomers dispersed into a structure of crystalline triglyceride in the solid carotene‐triglyceride mixtures. Practical applications: The amorphous structure of trans‐ and cis‐isomers in solid formulations of β‐carotene‐triglyceride mixtures will strongly affect their functional properties related to nutrition and color as food ingredients.

Aim Geographic mapping of risks is a useful analytical step in ecological risk assessments and in particular, in analyses aimed to estimate risks associated with introductions of invasive organisms. In this paper, we approach invasive species risk mapping as a portfolio allocation problem and apply techniques from decision theory to build an invasion risk map that combines risk and uncertainty in a single map product. Location Canada. Methods We divide the study area into a set of spatial domains and treat each domain as an individual ‘portfolio’ with a unique distribution of the expected impacts of invasion. The risk of invasion is then mapped by finding nested ‘efficient’ portfolio sets that identify the geographic areas exhibiting the worst combinations of the estimated risk of invasion and the uncertainty in that estimate. For Canadian municipalities, we apply the approach to quantify the risk that a given location will receive invasive forest pests with commercial freight transported via the North American road network. We compare risk allocation techniques that employ the concepts of nested mean-variance (M-V) frontiers and second-degree stochastic dominance. Results While both methods based on M-V and the stochastic dominance principles identified similar areas of highest risk, they differed in how they demarcated moderate-risk areas. Furthermore, they address uncertainty in different ways, treating it as a risk premium (in the case of nested M-V frontiers) or producing risk-averse delineations (in the case of stochastic dominance). Main conclusions The portfolio-based approach offers a viable strategy for dealing with the typically wide variability in risk estimates caused by a lack of knowledge about a new invader. The methodology also provides a tractable way of incorporating decision-making preferences into the final risk estimates and thus better aligns risk assessments with particular decision-making scenarios about the organism of concern.

Long-distance introductions of new invasive species have often been driven by socioeconomic factors, such that traditional “biological” invasion models may not be capable of estimating spread fully and reliably. In this study we present a new methodology to characterize and predict pathways of human-assisted entries of alien forest insects. We have developed a stochastic quantitative model of how these species may be moved with commodity flow through a network of international marine ports and major transportation corridors in Canada. The study makes use of a Canadian roadside survey database and data on Canadian marine imports, complemented with geo-referenced information on ports of entry, populated places and empirical observations of historical spread rates for invasive pests. The model is formulated as a probabilistic pathway matrix, and allows for quantitative characterization of likelihoods and vectors of new pest introductions from already or likely-to-be infested locations. We applied the pathway model to estimate the rates of human-assisted entry of alien forest insect species across Canada as well as cross-border transport to locations in the US. Results suggest a relatively low nationwide entry rate for Canada when compared to the US (0.338 new forest insect species per year vs. 1.89). Among Canadian urban areas, Greater Toronto and Greater Vancouver appear to have the highest alien forest insect entry potential, exhibiting species entry rates that are comparable with estimated rates at mid-size US urban metropolises.

Aim Uncertainty has been widely recognized as one of the most critical issues in predicting the expansion of ecological invasions. The uncertainty associated with the introduction and spread of invasive organisms influences how pest management decision makers respond to expanding incursions. We present a model-based approach to map risk of ecological invasions that combines two potentially conflicting goals: (1) estimating the likelihood of a new organism being established at a given locale and (2) quantifying the uncertainty of that prediction. Location Eastern and central Canada. Methods Our methodology focuses on the potential for long-distance, humanassisted spread of invasive organisms. First, we used a spatial simulation model to generate distributions of plausible invasion outcomes over a target geographical region. We then used second-degree stochastic dominance (SSD) criteria to rank all geographical locations in the target region based on these distributions. We applied the approach to analyze pathways of human-assisted spread (i.e., with commercially transported goods) of the emerald ash borer (EAB) (Agrilus planipennis Fairmaire), a major pest of ash trees in North America. Results The projected potential of the pest to establish at remote locations is significantly shaped by the amount of epistemic uncertainty in the model-based forecasts. The estimates based on the SSD ranking identified major ‘crossroads’ through which the movement of the EAB with commercial transport is most likely to occur. The system of major expressways in Ontario and Quebec was confirmed as the primary gateway of the pest’s expansion throughout the Canadian landscape. Main conclusions Overall, the new approach generates more realistic predictions of long-distance introductions than models that do not account for severe uncertainties and thus can help design more effective pest surveillance programmes. The modelling technique is generic and can be applied to assess other environmental phenomena when the level of epistemic uncertainty is high.

Aqueous reaction conditions that activate various aryl chlorides in Suzuki-Miyaura cross-coupling have been developed. These environment friendly conditions utilize ligandless Pd/C (Pd concentrations 0.2-2 mol%) that allow easy separation of the catalyst at the end of the reaction.

Pd on activated carbon (Pd/C) is demonstrated to be active and selective as one single catalyst in a series of one-pot multi-step reactions. The carefully chosen Pd/C catalysts were successfully applied in domino and tandem reactions involving (1) Heck reactions and hydrogenations for the synthesis of (a) dibenzyl and (b) 2-styryl-phenylamine, (2) Sonogashira coupling and intramolecular heteroannulation to form indole ring systems, and (3) Heck and Suzuki coupling reactions to produce 4-styryl-biphenyl. Total yields between 72 and 93% could be achieved. All reaction steps were performed with one and the same Pd/C catalyst, solvent, and additives. Temperature and pressure were adjusted as necessary. The order of the different reactions, the consecutive addition of educt(s) and optimization of reaction conditions was found to be crucial.

Palladium modified zeolites exhibit a high activity towards the Heck reaction of aryl bromides with styrene for small Pd concentrations (=0.2 mol%). The catalysts can be easily separated from the reaction mixture and reused without loss in activity. Leaching of active Pd species was observed in dependence on the zeolite structure. The electronic nature of the aryl bromide has a dominating effect on the reaction yield and the results observed are consistent with an oxidative addition of the aryl bromide to a Pd(0) centre via a S N Ar route.

Copper(II) complexes with N-2-aminoethyl-3-aminopropyltnmethoxysilane (N – N) as an ethylenediamme analogue were analysed prior to the sol–gel process, during the reaction (N – N + tetramethoxysilane) with water and in the gel products, to determine the coordination environment of the central ion. The results of EPR, thermal decomposition and CuII adsorption studies are summarized in three identified models of the coordination sites in the gels. Partial conversion of the bis- to mono-[N – N] environment of CuII during the transition from the sol to the gel is observed. There is also EPR evidence of the existence of another copper(II) site, the coordination sphere of which was not identified.

Long-distance introductions of alien species are often driven by socioeconomic factors, such that conventional "biological" invasion models may not be capable of estimating spread fully and reliably. In this study, we demonstrate a new technique for assessing and reconstructing human-mediated pathways of alien forest species entries to major settlements in Canada via commercial road transportation and domestic trade. We undertook our analysis in three steps. First, we used existing data on movement of commodities associated with bark- and wood-boring forest pests to build a probabilistic model of how the organisms may be moved from one location to another through a transportation network. We then used this model to generate multiple sets of predictions of species arrival rates at every location in the transportation network, and to identify the locations with the highest likelihood of new incursions. Finally, we evaluated the sensitivity of the species arrival rates to uncertainty in key model assumptions by testing the impact of additive and multiplicative errors (by respectively adding a uniform random variate or symmetric variation bounds to the arrival rate values) on the probabilities of pest transmission from one location to another, as well as the impact of the removal of one or more nodes and all connecting links to other nodes from the underlying transportation network. Overall, the identification of potential pest arrival hotspots is moderately robust to uncertainties in key modeling assumptions. Large urban areas and major border crossings that have the highest predicted species arrival rates have the lowest sensitivities to uncertainty in the pest transmission potential and to random changes in the structure of the transportation network. The roadside survey data appears to be sufficient to delineate major hubs and hotspots where pests are likely to arrive from other locations in the network via commercial truck transport. However, "pass-through" locations with few incoming and outgoing routes can be identified with lower precision. The arrival rates of alien forest pests appear to be highly sensitive to additive errors. Surprisingly, the impact of random changes in the structure of the transportation network was relatively low.

Heterogeneous palladium catalysts are highly active for Suzuki coupling reactions in neat water and in the presence of tetrabutylammonium bromide under mild conditions.

Two series (A and B) of organically modified silicate gels complexed with CuII have been synthesized by a twostep reaction procedure: (1) coordination, (2) sol–gel process. Series A consists of unidentate ligands [L]= H2N(CH2)3SiO3/2 and series B of bidentate ligands [L′]= H2N(CH2)2NH(CH2)3SiO3/2. The gels complexed in bulk with CuII have been analysed by electron paramagnetic resonance EPR spectroscopy at specific stages of thermal decomposition. The EPR data are complemented with thermoanalytical methods: differential thermal analysis (DTA), differential thermogravimetry (DTG) and thermogravimetry (TG).

This paper reports an alternative method for seasonal and long-term monitoring of biomass and the leaf area index (LAI) at Arctic tundra sites. Information related to the historical and projected change in abundance and distribution of biomass and LAI is required to address numerous environmental and resource management issues. Observations of earth from satellites could potentially be used to derive seasonal and long-term changes in biomass and the LAI. To realize this potential, seasonal and long-term ground monitoring data for validation are essential; however, the conventional destructive sampling method for measuring biomass and the LAI does not allow repetitive measurements at the same plots and thus is not suitable for monitoring change over time. Alternative methods, such as sampling nearby similar plots, can be laborious and easily subject to large sampling errors, especially in Arctic tundra sites with low vegetation cover. In this study, we developed a practical method for relating non-destructive measurements (percent cover and mean height) to biomass and the LAI for 13 major Arctic plant groups, or seven plant functional types, on the basis of measurements at 196 plots across Canada’s Arctic tundra ecosystems. Using the method at the plant group level to estimate plot total vascular aboveground biomass, foliage biomass, and LAI, we had r 2 = 0.91–0.95 and relative mean absolute error of 25–29%. By this method, one could monitor seasonal and long-term changes in biomass and the LAI through repeated, non-destructive observations of percent cover and mean height at the same permanent plots.

The influence of the Mg doping profile on the electroluminescence efficiency of GaInN light emitting diodes (LED) has been investigated. The Mg doping profile is influenced by segregation as well as by diffusion during the growth. The diffusion of the Mg dopants into the active region can be controlled by the growth temperature of the Mg doped layers. An increase in Mg concentration close to the active region results in an improved hole injection and thus in a higher electroluminescence efficiency of the GaInN quantum wells. However an excessive spread of the Mg doping atoms towards the GaInN quantum well active region leads to nonradiative recombination and thus a lower output power of the LEDs. An LED test structure containing multiple quantum wells which differ in In content and emission wavelength was used to probe the spatial distribution of the radiative recombination of electrons and holes in the active region and to clarify the influence of Mg dopants in the active region on nonradiative recombination.

Heck reactions of aryl bromides with cyclohexene and cyclopentene catalyzed by typical homogeneous as well as heterogeneous Pd catalysts (Pd/C, Pd/SiO 2 , Pd/MgO, Pd/Al 2 O 3 , and Pd(0), Pd(II) and [Pd(NH 3 ) 4 ] 2+ in zeolites Y or ZSM-5) have been studied in order to get detailed information on the reaction mechanism with regard to the catalyst. The focus of the present investigation was on correlations between selectivity (Heck products: double bond isomers of arylcycloalkenes, dehalogenation and double arylation products) and nature of the catalyst or active Pd species, respectively. The results indicate that dissolved molecular Pd species are responsible for the Heck coupling for both homogeneous and heterogeneous (solid) catalysts, whereas dehalogenation is due to a mechanism involving the surface of solid Pd metal particles and radical processes. The selectivity of the reactions can be controlled by the choice of catalyst and reaction conditions (base, solvent, temperature).

Flip-chip-mounting of integrated circuits has been shown as an effective way to connect integrated circuits with substrates providing highest bandwidths. This technique also has been used to connect chips directly without causing significant parasitics. In this paper, hybrid integrated photoreceivers with large bandwidths for fiber-optic data transmission will be discussed. Several photoreceivers with bandwidths of more than 60 GHz have been fabricated by combining photodiodes and amplifiers, which have been optimised in separated wafer runs. Key features of this type of photoreceivers are a waveguide photodiode with a high responsivity (0.8 A/W) and a traveling wave amplifier with low input impedance as well as high amplification to a 50 Ω output termination up to 65 GHz. Further improvement of bandwidth is expected by using metamorphic HEMTs instead of pseudomorphic ones in the amplifier.

Investigations of transient photoluminescence induced by external electric fields parallel to the layers of GaAs/Al0.35Ga0.65As quantum wells are reviewed. The photoluminescence was detected by time-correlated single-photon counting technique at liquid nitrogen and liquid helium temperatures applying electric fields of nanosecond duration to the wells of different width. It is shown how experimentally one can resolve between excitonic and donor impact ionization processes in combining spectral and time domains. From the study of the spectral-temporal dynamics at initial moments we have determined the coefficient of exciton impact ionization as a function of electric field for various widths of the quantum wells.© (2003) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We report on the development of (AlGaIn)N quantum well LEDs covering the 380 to 430 nm wavelength range, which serve as the primary light source for tri-phosphor luminescence conversion white LEDs. Epitaxial layer growth was performed by low-pressure metal-organic chemical vapor deposition on sapphire substrates. Mesa LEDs were fabricated and either mounted in standard epoxy-based 5 mm radial LED packages or flip-chip bonded on ceramic submounts. Then, LED-chips with peak wavelengths matching the absorption spectrum of an appropriately chosen inorganic tri-phosphor blend, were used for the fabrication of single-chip tri-color luminescence conversion white LEDs. These de-vices allowed us to demonstrate the feasibility of the above concept for improved color rendering and tunability.

The luminescence induced by alpha particles in GaAs/Al0.35Ga0.65As multiple quantum well (MQW) semiconductor was detected and investigated. The luminescence was observed at liquid nitrogen and at room temperatures as light flashes induced by individual (alpha) -particles. The MQW samples studied, in addition, were investigated using standard photoluminescence method to show that (alpha) - particle created flashes are associated with a radiative decay of 2D excitons in quantum wells. Since the number of detected light quanta in a flash is critical, a discussion of the collection efficiency of photons created by a single (alpha) -particle is presented.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

[Pd]-exchanged NaY zeolites have been prepared, characterized, and applied for the first time for catalytic carbon-carbon coupling reactions. The catalysts exhibit a high activity and selectivity toward the Heck reaction of aryl bromides with olefins for small palladium concentrations (< or =0.1 mol % of Pd). The catalysts can easily be separated from the reaction mixture and reused after washing without loss in activity. No limitation to the diffusion of adducts in the zeolite cages was observed (for linear alkenes). The electronic nature of the aryl bromides and the olefins has a dominating effect on the reaction yield and selectivity. The heterogeneous catalysts quantitatively convert all types of all aryl bromide (complete conversion of bromobenzene within 30 min) and activated aryl chlorides under standard reaction conditions. Product form selectivity is observed in the Heck reaction with cyclic olefins.

For the first time, monolithic optoelectronic receivers for a wavelength of 1.3 micrometers have been fabricated successfully on GaAs substrates using InGaAs metal-semiconductor-metal (MSM) photodiodes and AlGaAs/GaAs/AlGaAs high-electron-mobility transistors (HEMTs). Using molecular beam epitaxy (MBE), the photodetector layers were grown on top of a double (delta) -doped AlGaAs/GaAs/AlGaAs HEMT structure which allows the fabrication of enhancement and depletion field effect transistors. The photoabsorbing InGaAs layer was grown at 500 degree(s)C. To fabricate the optoelectronic receivers, first, an etch process using a combination of non-selective wet etching and selective reactive ion etching was applied to produce mesas for the photoconductors and to uncover the HEMT structure in all other areas. For the electronic circuits, our well-established HEMT process for 0.3-micrometers transistor gates was used which includes electron-beam lithography for gate definition and optical lithography for NiCr thin films resistors, capacitors, and inductors. The interdigitated MSM photodiode fingers were also fabricated using electron-beam lithography. For interconnecting the electronic circuits and the photodetectors, air bridges were employed. The entire process was performed on 2-inch wafers with more than 90% yield of functional receivers. The finished receiver--basically an MSM photodetector linked to a transimpedance amplifier--is operational at an incident wavelength of 1.3 micrometers at data rates up to 1.2 Gbit/s. The sensitivity of the detectors is 0.16 A/W at a 10 V bias.

Sub-0.1 micrometers mushroom-shaped gates (T-gates) have been realized with a three-layer resist technique using e-beam exposure. The exposure was carried out on a Philips EPBG-3 system operating at 50 kV. The resist system and writing strategy were investigated. Test exposures on SiN-capped GaAs wafers with ohmic contacts having the same topography as active devices were carried out. Using this T-gate lithography, pseudomorphic AlGaAs/InGaAs/GaAs HEMTs were fabricated. These devices have transit frequencies of 120 GHz.

Stimulated emission in indirect band-gap Al(x)Ga(1-x)As is observed at room temperature. This indirect stimulated emission is based on alloy-disorder induced zero-phonon band-to-band transitions. A quadratic dependence of the threshold pump intensity on the energy separation of the renormalized direct and indirect conduction bands is found. These threshold excitation intensities show a weak exponential increase with lattice temperature. The emission wavelength and the emission intensity close to the crossover composition are strongly influenced by band-gap renormalization, which is treated in a multivalley model. This model quantitatively explains the enhanced gap shrinkage in direct-gap AlGaAs close to the crossover composition.

Electron and hole tunneling transfer processes in asymmetric double quantum well structures are investigated by time-resolved picosecond photoluminescence. Change from nonresonant to resonant tunneling is achieved with a perpendicular eleitric field. Electron transfer times decrease if the two electron subbands in the two quantum wells are energetically aligned. Both nonresonant and resonant electron transfer times decrease strongly with the barrier thickness. The resonant times are more than one order of magnitude smaller than the nonresonant times for the same barrier thickness. The buildup of delocalized coherent states at resonance would lead to much shorter resonant transfer times than we observe experimentally. This discrepancy is discussed in terms of state broadening. Hole transfer times also decrease at specific electric fields showing a resonance feature, which can be attributed either to the resonant transfer of n=1 heavy holes to an n=1 light hole level or to the onset of the optical phonon scattering from the n=1 heavy hole level to the neighbouring n=1 heavy hole level.© (1990) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.