Micelle assisted thin-film solid phase microextraction: a new approach for determination of quaternary ammonium compounds in environmental samples

Determination of quaternary ammonium compounds (QACs) often is considered to be a challenging undertaking owing to secondary interactions of the analytes’ permanently charged quaternary ammonium head or hydrophobic tail with the utilized lab-wares. Here, for the first time, a micelle assisted thin-film solid phase microextraction (TF-SPME) using a zwitterionic detergent 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate (CHAPS) as a matrix modifier is introduced as a novel approach for in-laboratory sample preparation of the challenging compounds. The proposed micelle assisted thin-film solid phase microextraction (TF-SPME) method offers suppression/enhancement free electrospray ionization of analytes in mass spectrometric detection, minimal interaction of the micelles with the TF-SPME coating, and chromatographic stationary phase and analysis free of secondary interactions. Moreover, it was found that the matrix modifier has multiple functions; when its concentration is found below the critical micelle concentration (CMC), the matrix modifier primarily act as a surface deactivator; above its CMC, it acts as a stabilizer for QACs. Additionally, shorter equilibrium extraction times in the presence of the modifier demonstrated that micelles also assist in the transfer of analytes from the bulk of the sample to the surface of the coating. The developed micelle assisted TF-SPME protocol using the 96-blade system requires only 30 min of extraction and 15 min of desorption. Together with a conditioning step (15 min), the entire method is 60 min; considering the advantage of using the 96-blade system, if all the blades in the brush are used, the sample preparation time per sample is 0.63 min. Moreover, the recoveries for all analytes with the developed method were found to range within 80.2%- 97.3%; as such, this method can be considered an open bed solid phase extraction. The proposed method was successfully validated using real samples.NSERC Industrial Research Chair || NSERC IRCPJ/184412-10 05016

Consumer taste uncertainty in the context of store brand and national brand competition

In this paper, we focus on the uncertainty in consumer taste and study how a retailer can benefit from acquiring that taste information in the presence of competition between the retailer's store brand and a manufacturer's national brand. In this context, we also identify the optimal information sharing strategy of the retailer with the manufacturer as well as the equilibrium product positioning and pricing of the two brands. We model a competitive setting in which there is ex-ante uncertainty about consumer preferences for different product features and the retailer has a distinct advantage in terms of resolving this uncertainty, given his close proximity to the consumers. We identify two important effects of retailer's information acquisition and sharing decisions about consumer taste. The direct effect is that having taste information allows the retailer to make better SB introduction and positioning decisions. The indirect effect is that information sharing enables the manufacturer to make better NB positioning decisions - which in return may benefit or hurt the retailer. Furthermore, we show that these effects interact with each other and the nature of their interaction depends on three external factors: relative popularity of different product features, the vertical differentiation between the two brands, and the cost of store brand introduction. This interaction is most striking when the store brand introduction is not very costly. In this case, if one of the features is quite popular, then the retailer voluntarily shares information with the manufacturer because the indirect effect augments the value of the direct effect - even though this increases the competition between the brands. Otherwise, the retailer refrains from information sharing because the indirect effect then diminishes the value of the direct effect. We also generate managerial insights as to when it is most valuable for the retailer to acquire taste information as well its worth for the manufacturer

Approximation methods for large-scale spatial queueing systems

Different than the conventional queueing systems, in spatial queueing systems (SQS) the service rate for each customer-server pairs differs and the server that intervenes for a specific customer is not known a priori, depending on the availability of servers at the moment a request was made. These features make the SQS computationally expensive (almost intractable for large scale) but at the same time more suitable for real-life problems with high reliability expectations. Emergency response and on-demand transportation systems are two similar systems that can be modeled with the SQS. In this research, we aim to solve facility location problems as SQS with stochastic demand and service time. The stochasticity concerned here is temporal and spatial, that emerges from the uncertainty in the demand and service time. In order to tackle this problem Larson (1974)'s 2n hypercube queueing model (HQM) is extended to 3n HQM. In this model, there are two different possible service types for each server: (i) service for locations in the proximity of a server (area of responsibility) and (ii) service for other locations where the first responsible server is busy during this event. In addition, to decrease the dimension of the problem, which is intractable due to their size, a new 3n aggregate hypercube queueing model (AHQM) is developed that treats group of servers (bins) in a similar manner by considering interactions among bins. An efficient graph partitioning algorithm is proposed to cluster servers in groups with an objective to minimize the interactions among groups. Both exact and approximate approaches are integrated inside two optimization methods (i.e. variable neighborhood search and simulated annealing) to find server locations that improve system performance. Computational experiments showed that both models are applicable to use inside optimization algorithms to find good server locations and to improve system performance measures of SQS

Consumer Willingness-To-Pay for Different Organic Certification Logos in Turkey

Using data from focus group discussions with consumers and a choice experimentconducted in some of Turkey’s major cities, this study investigates whetherTurkish consumers prefer certain organic labelling schemes over others attemptsand to elicit their willingness to pay (WTP) for different organic certificationlogos. Although the level of awareness regarding organic certification logos waslow, consumers’ perceptions of the logos were generally positive. The results ofthe random parameter logit models indicated a positive WTP for the presence ofone of the three tested certification body logos in addition to the mandatorygovernmental logo. Given the low level of certification logo awareness, theconclusion is that both purchasing decisions and perceptions regarding logoswere affected by subjective criteria. Both the government and certification bodiesshould develop measures to increase consumer awareness of their logos and formconsumer perceptions and attitudes regarding the quality of the certificationimplied by the logo

Factors influencing the perception of organic certification logos in Turkey

Consumers’ perceptions on organic certification logos and the factors influencing these perceptions were explored. Data from surveys conducted in major cities of Turkey revealed that organic food consumers had little knowledge about logos, although the declared level of trust in organic logos was high. According to ordered logit models, consumer’s perceptions on organic certification logos were influenced by purchasing frequency and weight of organic foods in total food consumption. Dummy variables representing additional private certification company logos as well were generally found to have a significant effect on logo perception. This result suggests that consumers’ attitudes towards these logos and towards the governmental logo are not the same. Female and older people were more sceptical about the trustworthiness of the logos. While the credibility of the logos and the standards and control systems underlying the logos increased as frequency of purchasing organic food increased, those consumers who prefer organic open markets for buying organic food were hesitant to trust the credibility of the organic certification logos. The mandatory governmental logo and the underlying standards are trusted more than the private company logos. However, the difference of the attitudes toward logos decreases when the control system is in question. When a comparison between perceptions towards labels including different additional certification companies’ logos is made, the additional logo was found to affect the stated preferences more negatively when the companies were foreign. Enhanced interest and trust in the organic certification logos among consumers would foment the development of the organic sector, and the findings of this paper serve as an input for the achievement of this aim

Measurements of DNS Stability

In this project, we measured the stability of DNS servers based on the most popular 500 domains. In the first part of the project, DNS server replica counts and maximum DNS server separation are found for each domain. In the second part, these domains are queried for a one-month period in order to find their uptime percentages

Effect of contiguity and figure-ground organization on the area rule of lightness

Cataloged from PDF version of article.In a simple two-dimensional (2D) display composed of two uniform surfaces with different luminances, the lightness of the darker surface varies as a function of its relative area while its luminance is held constant (Gilchrist & Radonjić, 2009; Li & Gilchrist, 1999). This phenomenon is known as the area rule of lightness, and although it is extensively studied in the literature, the underlying principles are still largely unknown. Here, using computer-generated stimuli, we investigated the effects of contiguity and figure-ground organization on the area rule of lightness. Stimuli were 2D disks composed of radial sectors with high (25 cd/ m2) or low (8 cd/m2 ) luminance. On each trial, observers judged the lightness of the sectors by adjusting the luminance of a matching patch. Four conditions were tested. In the contiguous condition, there were one dark and one light sector, in the noncontiguous condition, both the light and dark surfaces were split into four equal radial sectors. Figure and ground conditions were generated by adding small contextual elements to the stimulus. We found that the area rule applied under all conditions; however, the functional form of the effect showed marked differences across conditions. Taken together, our results show that both high-level (e.g., perceptual grouping, figure-ground organization) and low-level (e.g., spatial-summation) mechanisms play a role in the area rule of lightness. © 2014 ARVO

Border ownership selectivity in human early visual cortex and its modulation by attention

Natural images are usually cluttered because objects occlude one another. A critical aspect of recognizing these visual objects is to identify the borders between image regions that belong to different objects. However, the neural coding of border ownership in human visual cortex is largely unknown. In this study, we designed two simple but compelling stimuli in which a slight change of contextual information could induce a dramatic change of border ownership. Using functional MRI adaptation, we found that border ownership selectivity in V2 was robust and reliable across subjects, and it was largely dependent on attention. Our study provides the first human evidence that V2 is a critical area for the processing of border ownership and that this processing depends on the modulation from higher-level cortical areas. Copyright © 2009 Society for Neuroscience