Showing papers by "Ryerson University published in 2007"
TL;DR: This paper covers the high-power voltage-source inverter and the most used multilevel-inverter topologies, including the neutral-point-clamped, cascaded H-bridge, and flying-capacitor converters.
Abstract: This paper presents a technology review of voltage-source-converter topologies for industrial medium-voltage drives. In this highly active area, different converter topologies and circuits have found their application in the market. This paper covers the high-power voltage-source inverter and the most used multilevel-inverter topologies, including the neutral-point-clamped, cascaded H-bridge, and flying-capacitor converters. This paper presents the operating principle of each topology and a review of the most relevant modulation methods, focused mainly on those used by industry. In addition, the latest advances and future trends of the technology are discussed. It is concluded that the topology and modulation-method selection are closely related to each particular application, leaving a space on the market for all the different solutions, depending on their unique features and limitations like power or voltage level, dynamic performance, reliability, costs, and other technical specifications.
2,254 citations
TL;DR: In this article, the authors emphasize the potential for improving green-roof function by understanding the interactions between its ecosystem elements, especially the relationships among growing media, soil biota, and vegetation.
Abstract: Green roofs (roofs with a vegetated surface and substrate) provide ecosystem services in urban areas, including improved storm-water management, better regulation of building temperatures, reduced urban heat-island effects, and increased urban wildlife habitat. This article reviews the evidence for these benefits and examines the biotic and abiotic components that contribute to overall ecosystem services. We emphasize the potential for improving green-roof function by understanding the interactions between its ecosystem elements, especially the relationships among growing media, soil biota, and vegetation, and the interactions between community structure and ecosystem functioning. Further research into green-roof technology should assess the efficacy of green roofs compared to other technologies with similar ends, and ultimately focus on estimates of aggregate benefits at landscape scales and on more holistic cost-benefit analyses.
1,137 citations
TL;DR: Improvements, effect of the different setting parameters, and functionality of the algorithm are shown in the scope of classical structural optimization problems, and results show the ability of the proposed methodology to find better optimal solutions for structural optimization tasks than other optimization algorithms.
646 citations
TL;DR: Results suggest that community gardens were perceived by gardeners to provide numerous health benefits, including improved access to food, improved nutrition, increased physical activity and improved mental health, and were seen to promote social health and community cohesion.
Abstract: SUMMARY This article describes results from an investigation of the health impacts of community gardening, using Toronto, Ontario as a case study. According to community members and local service organizations, these gardens have a number of positive health benefits. However, few studies have explicitly focused on the health impacts of community gardens, and many of those did not ask community gardeners directly about their experiences in community gardening. This article sets out to fill this gap by describing the results of a community-based research project that collected data on the perceived health impacts of community gardening through participant observation, focus groups and in-depth interviews. Results suggest that community gardens were perceived by gardeners to provide numerous health benefits, including improved access to food, improved nutrition, increased physical activity and improved mental health. Community gardens were also seen to promote social health and community cohesion. These benefits were set against a backdrop of insecure land tenure and access, bureaucratic resistance, concerns about soil contamination and a lack of awareness and understanding by community members and decisionmakers. Results also highlight the need for ongoing resources to support gardens in these many roles.
577 citations
TL;DR: The findings suggest that the STICSA may be a purer measure of anxiety symptomatology than is the STAI.
Abstract: The State-Trait Inventory for Cognitive and Somatic Anxiety (STICSA; M. J. Ree, C. MacLeod, D. French, & V. Locke, 2000) was designed to assess cognitive and somatic symptoms of anxiety as they pertain to one's mood in the moment (state) and in general (trait). This study extended the previous psychometric findings to a clinical sample and validated the STICSA against a well-published measure of anxiety, the State-Trait Anxiety Inventory (STAI; C. D. Spielberger, 1983). Patients (N=567) at an anxiety disorders clinic were administered a battery of questionnaires. The results of confirmatory factor analyses (Bentler-Bonnett nonnormed fit index, comparative fit index, and Bollen fit index>.90; root-mean-square error of approximation /=.64), the STICSA was more strongly correlated with another measure of anxiety (rs>/=.67) and was less strongly correlated with a measure of depression (rs
522 citations
TL;DR: Pay for performance has been proposed as a solution to this problem as discussed by the authors, and has been shown to be effective in solving the problem of imperfect alignment of the interests of owners and employees.
Abstract: Agency theory highlights losses in productivity that may occur when the interests of owners and employees are imperfectly aligned. Pay for performance has been proposed as a solution to this proble...
367 citations
TL;DR: In this article, the authors investigate what it means for corporate social responsibility to be "mainstreamed" in a company and reveal that mainstreaming can be understood in terms of three distinct CSR orientations: the business-case model, the syncretic stewardship model, and the social values-led model.
Abstract: This article investigates what it means for corporate social responsibility (CSR) to be "mainstreamed" in a company. Rather than a single ' best practice/narratives provided by managers revealed that mainstreaming can be understood in terms of three distinct CSR orientations: the business-case model, the syncretic stewardship model, and the social values-led model. These different orientations and approaches to mainstreaming CSR are the result of three inter-related factors: an "external market for virtue/an "internal market for virtue/and the established culture of the company. For business case and social values-led firms, incentives can be developed that encourage them to gravitate toward the syncretic stewardship orientation, which may well represent the most sustainable dimension of CSR.
352 citations
TL;DR: The work hardening properties of a friction stir welded (FSWed) magnesium alloy were evaluated using two modified equations of hardening capacity and strain hardening exponent where the elastic deformation stage was excluded.
338 citations
TL;DR: It is shown that in an oligopoly, the total reduction in the cost due to the innovation for the pre-innovation competitive output forms the lower bound of the payoffs of both outsider and incumbent innovators.
307 citations
TL;DR: This paper is to capitalize on experience gained from two decades of conducting EB studies around the world to illustrate that the EB methodology, if properly undertaken, produces results that could be substantially different and less biased than those from more conventional types of studies.
264 citations
TL;DR: These represent likely extra- and intracellular antioxidant activities of flax-derived lignans at concentrations potentially achievable in vivo, andBenzylic hydrogen abstraction and potential resonance stabilization of phenoxyl radicals in an aqueous environment likely contributed to the antioxidant activity of the mammalian lignan.
TL;DR: In this article, the effect of reinforcement bar ratio ρ on the flexural strength of reinforced concrete beams strengthened using Carbon Fibre Reinforced Polymers (CFRP) sheets is examined.
TL;DR: Perceived organizational support had both a unit-level and an employee-level effect on 1 dimension of service quality: helping behavior, and affective commitment to customers enhanced service quality.
Abstract: The authors examined the relationships between perceived organizational support, organizational com-mitment, commitment to customers, and service quality in a fast-food firm. The research design matchedcustomer responses with individual employees’ attitudes, making this study a true test of the serviceprovider–customer encounter. On the basis of a sample of matched employee–customer data ( N 133),hierarchical linear modeling analyses revealed that perceived organizational support had both a unit-leveland an employee-level effect on 1 dimension of service quality: helping behavior. Contrary to affectiveorganizational commitment, affective commitment to customers enhanced service quality. The 2 subdi-mensions of continuance commitment to the organization—perceived high sacrifice and perceived lackof alternatives—exerted effects opposite in sign: The former fostered service quality, whereas the latterreduced it. The implications of these findings are discussed within the context of research on employee–customer encounters.Keywords: perceived organizational support, organizational committment, commitment to customers,service quality
Journal Article•
TL;DR: In this article, a robust control scheme with an outer Hinfin voltage control loop and an inner current control loop is designed and implemented on a medium-voltage (MV)-level dynamic voltage restorer (DVR) system.
Abstract: In this paper, a robust control scheme with an outer Hinfin voltage control loop and an inner current control loop is designed and implemented on a medium-voltage (MV)-level dynamic voltage restorer (DVR) system. Through a simple selection of weighting functions, the synthesized Hinfin controller would exhibit significant gains in the vicinity of positive- and negative-sequence fundamental frequencies, and therefore, it would be able to regulate both positive- and negative-sequence components effectively, with explicit robustness in the face of system parameter variations. A detailed discussion of Hinfin controller weighting function selection, inner current loop tuning, and system disturbance rejection capability is presented. Finally, the designed control scheme is extensively tested on a laboratory 10-kV MV-level DVR system with varying voltage sag (balanced and unbalanced) and loading (linear/nonlinear load and induction motor load) conditions. It is shown that the proposed control scheme is effective in both balanced and unbalanced sag compensation and load disturbance rejection, as its robustness is explicitly specified.
TL;DR: It is shown that the proposed control scheme is effective in both balanced and unbalanced sag compensation and load disturbance rejection, as its robustness is explicitly specified.
Abstract: In this paper, a robust control scheme with an outer Hinfin voltage control loop and an inner current control loop is designed and implemented on a medium-voltage (MV)-level dynamic voltage restorer (DVR) system. Through a simple selection of weighting functions, the synthesized Hinfin controller would exhibit significant gains in the vicinity of positive- and negative-sequence fundamental frequencies, and therefore, it would be able to regulate both positive- and negative-sequence components effectively, with explicit robustness in the face of system parameter variations. A detailed discussion of Hinfin controller weighting function selection, inner current loop tuning, and system disturbance rejection capability is presented. Finally, the designed control scheme is extensively tested on a laboratory 10-kV MV-level DVR system with varying voltage sag (balanced and unbalanced) and loading (linear/nonlinear load and induction motor load) conditions. It is shown that the proposed control scheme is effective in both balanced and unbalanced sag compensation and load disturbance rejection, as its robustness is explicitly specified.
TL;DR: PLS analysis of survey data collected from 209 employees in seven organizations that had engaged in a large-scale IT implementation revealed that project champion charisma was positively associated with increased performance expectancy, effort expectancy, social influence and facilitating condition perceptions of users.
Abstract: Although there is widespread agreement that leadership has important effects on information technology (IT) acceptance and use, relatively little empirical research to date has explored this phenomenon in detail. This paper integrates the unified theory of acceptance and use of technology (UTAUT) with charismatic leadership theory, and examines the role of project champions influencing user adoption. PLS analysis of survey data collected from 209 employees in seven organizations that had engaged in a large-scale IT implementation revealed that project champion charisma was positively associated with increased performance expectancy, effort expectancy, social influence and facilitating condition perceptions of users. Theoretical and managerial implications are discussed, and suggestions for future research in this area are provided.
TL;DR: A FE model, previously validated by the authors to represent the geometry of a synthetic femur, was used with a range of input material properties and change in geometric size, to establish whether cadaveric results could be simulated, and was able to successfully simulate both the behavior of the 3GCF, and a wide range of cADAveric bone data scatter.
Abstract: To assess the performance of femoral orthopedic implants, they are often attached to cadaveric femurs, and biomechanical testing is performed. To identify areas of high stress, stress shielding, and to facilitate implant redesign, these tests are often accompanied by finite element (FE) models of the bone/implant system. However, cadaveric bone suffers from wide specimen to specimen variability both in terms of bone geometry and mechanical properties, making it virtually impossible for experimental results to be reproduced. An alternative approach is to utilize synthetic femurs of standardized geometry, having material behavior approximating that of human bone, but with very small specimen to specimen variability. This approach allows for repeatable experimental results and a standard geometry for use in accompanying FE models. While the synthetic bones appear to be of appropriate geometry to simulate bone mechanical behavior, it has not, however, been established what bone quality they most resemble, i.e., osteoporotic or osteopenic versus healthy bone. Furthermore, it is also of interest to determine whether FE models of synthetic bones, with appropriate adjustments in input material properties or geometric size, could be used to simulate the mechanical behavior of a wider range of bone quality and size. To shed light on these questions, the axial and torsional stiffness of cadaveric femurs were compared to those measured on synthetic femurs. A FE model, previously validated by the authors to represent the geometry of a synthetic femur, was then used with a range of input material properties and change in geometric size, to establish whether cadaveric results could be simulated. Axial and torsional stiffnesses and rigidities were measured for 25 human cadaveric femurs (simulating poor bone stock) and three synthetic "third generation composite" femurs (3GCF) (simulating normal healthy bone stock) in the midstance orientation. The measured results were compared, under identical loading conditions, to those predicted by a previously validated three-dimensional finite element model of the 3GCF at a variety of Young's modulus values. A smaller FE model of the 3GCF was also created to examine the effects of a simple change in bone size. The 3GCF was found to be significantly stiffer (2.3 times in torsional loading, 1.7 times in axial loading) than the presently utilized cadaveric samples. Nevertheless, the FE model was able to successfully simulate both the behavior of the 3GCF, and a wide range of cadaveric bone data scatter by an appropriate adjustment of Young's modulus or geometric size. The synthetic femur had a significantly higher stiffness than the cadaveric bone samples. The finite element model provided a good estimate of upper and lower bounds for the axial and torsional stiffness of human femurs because it was effective at reproducing the geometric properties of a femur. Cadaveric bone experiments can be used to calibrate FE models' input material properties so that bones of varying quality can be simulated.
TL;DR: In this article, the development and applicability of Vapex is brought up in context of the availability of oil from natural sources, challenges of oil recovery, environmental factors, and cost economics.
Abstract: The vapor extraction of heavy oil and bitumen, or Vapex, has emerged as a very promising recovery process since its invention in 1991. The principal reason is the environmental friendliness of Vapex together with its cost-effective nature vis-a-vis other recovery processes. This paper assimilates and presents the research and technological contributions made toward Vapex. The development and applicability of Vapex is brought up in context of the availability of oil from natural sources, challenges of oil recovery, environmental factors, and cost economics. Significant findings and salient features of several experimental and theoretical studies on Vapex are included. Various factors that influence the operation of Vapex are discussed. Important issues are identified that need further investigations for the continued enhancement of Vapex. It is expected that this paper will serve as a useful reference tool for the engineers and scientists interested in Vapex.
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TL;DR: In the investigation reported here, it is considered whether the facial expressions and head movements of singers communicate melodic information that can be ‘‘read’’ by viewers.
Abstract: From the phonograph of the 19th century to the iPod today, music technologies have typically isolated the auditory dimension of music, filtering out nonacoustic information and transmitting what most people assume is the essence of music. Yet many esteemed performers over the past century, such as Judy Garland and B.B. King, are renowned for their dramatic use of facial expressions (Thompson, Graham, & Russo, 2005). Are such expressions merely show business, or are they integral to experiencing music? In the investigation reported here, we considered whether the facial expressions and head movements of singers communicate melodic information that can be ‘‘read’’ by viewers. Three trained vocalists were recorded singing ascending melodic intervals. Subjects saw the visual recordings (without sound) and rated the size of the intervals they imagined the performers were singing.
12 Dec 2007
TL;DR: A real-time electromyography (EMG) classifier of user-selected intentional movements rather than an imposed subset of standard movements may facilitate the development of dynamic upper extremity prosthesis control strategies using arbitrary, user-preferred muscle contractions.
Abstract: Pattern recognition-based multifunction prosthesis control strategies have largely been demonstrated with subsets of typical able-bodied hand movements. These movements are often unnatural to the amputee, necessitating significant user training and do not maximally exploit the potential of residual muscle activity. This paper presents a real-time electromyography (EMG) classifier of user-selected intentional movements rather than an imposed subset of standard movements. EMG signals were recorded from the forearm extensor and flexor muscles of seven able-bodied participants and one congenital amputee. Participants freely selected and labeled their own muscle contractions through a unique training protocol. Signals were parameterized by the natural logarithm of root mean square values, calculated within 0.2 s sliding and non overlapping windows. The feature space was segmented using fuzzy C-means clustering. With only 2 min of training data from each user, the classifier discriminated four different movements with an average accuracy of 92.7% plusmn 3.2%. This accuracy could be further increased with additional training data and improved user proficiency that comes with practice. The proposed method may facilitate the development of dynamic upper extremity prosthesis control strategies using arbitrary, user-preferred muscle contractions.
TL;DR: In this article, the authors focused on the operational level of policy in order to gain a greater understanding of the barriers and possible solutions to implementation of sustainable tourism policy, and focused on one of the Mediterranean's most popular sun, sea and sand tourist resorts, located in Mallorca in the Balearic Islands, Spain.
Abstract: To date there is much literature identifying the need for sustainable tourism and for policy to address this need, however, there are few studies addressing sustainable tourism at a practical level or the effectiveness of policy implementation. This research focuses on the operational level of policy in order to gain a greater understanding of the barriers and possible solutions to implementation of sustainable tourism policy. This research focused on one of the Mediterranean's most popular sun, sea and sand tourist resorts – Calvia, located in Mallorca in the Balearic Islands, Spain. Calvia is an example of a mass tourism destination which, from a result of tourism pressure in the late 1980s, faced significant economic, social and environmental decline. By taking an integrated and collaborative approach to implement a sustainable tourism policy [using the participatory process of Local Agenda 21 (LA21)] Calvia received much international acclaim. This descriptive case study outlines the motivations behin...
TL;DR: In this paper, the authors explore the factors that contribute to and affect efforts to improve the public bus transit service in Indian cities, and suggest a disaggregated approach based on the needs and motivations of different groups in relation to public transit, along with improved operating conditions and policies to internalize costs of personal motor vehicle use.
Abstract: Maintaining and enhancing public transit service in Indian cities is important, to meet rapidly growing mass mobility needs, and curb personal motor vehicle activity and its impacts at low cost. Indian cities rely predominantly on buses for public transport, and are likely to continue to do so for years. However, the public bus transit service is inadequate, and unaffordable for the urban poor. The paper explores the factors that contribute to and affect efforts to improve this situation, based on an analysis of the financial and operational performance of the public bus transit service in the four metropolitan centres and four secondary cities during the 1990s. Overall, there were persistent losses, owing to increasing input costs and declining productivity. The losses occurred despite rapidly increasing fares, and ridership declined. The situation, and the ability to address it, is worse in the secondary cities than the metropolitan centres. We suggest a disaggregated approach based on the needs and motivations of different groups in relation to public transit, along with improved operating conditions and policies to internalize costs of personal motor vehicle use, to address the challenge of providing financially viable and affordable public bus transit service.
17 Jun 2007
TL;DR: This paper presents a modified PD-PWM technique, that combines the benefits of both modulation methods, achieving good output voltage and input current quality.
Abstract: Cascaded H-bridge multilevel inverters are commonly controlled using multicarrier Phase-Shifted PWM, since it allows an even power distribution among the converter power cells, which can lead to lower harmonic distortion in the input current if an adequate transformer is used. However it is known that other multicarrier methods, like Phase Disposition PWM (PD- PWM) have better output voltage quality with lower distortion. Nevertheless, when used with cascaded inverters, this method produces uneven usage of the converter cells, that disables the harmonic cancelations at the transformer input. This paper presents a modified PD-PWM technique, that combines the benefits of both modulation methods, achieving good output voltage and input current quality.
TL;DR: In this paper, an object-oriented approach for six Landsat TM and ETM+ images and simulating the land use pattern in the future using Markov Chain analysis and Cellular Automata analysis based on the interactions between these land uses and the transportation network is used to measure urban sprawl.
Abstract: This paper implements a land use classification for the City of Calgary, Alberta, Canada, using an object-oriented approach for six Landsat TM and ETM+ images and simulates the land use pattern in the future using Markov Chain analysis and Cellular Automata analysis based on the interactions between these land uses and the transportation network. Shannon’s Entropy (an urban sprawl index) based on the land use classification results is used to measure urban sprawl. This research proves that an object-oriented approach can produce satisfactory classification results. It reveals the manner in which land use is likely to develop in the future, and demonstrates that urban sprawl continued to grow in Calgary during the years between 1985 and 2001. Such models are useful for providing the building blocks for traditional four-step transportation planning models.
TL;DR: In this article, the influence of stabilizers and their combinations is evaluated through Atterberg limits, standard Proctor compaction, unconfined compressive strength, splitting tensile strength, modulus of elasticity and California bearing ratio.
Abstract: Papua New Guinea clayey soils are stabilized with various percentages of volcanic ash (VA), finely ground natural lime (L), cement and their combinations. The influence of stabilizers and their combinations is evaluated through Atterberg limits, standard Proctor compaction, unconfined compressive strength, splitting tensile strength, modulus of elasticity and California bearing ratio (CBR) tests. The durability of 38 stabilized soil mixtures is also conducted by studying the influence of water immersion on strength, water sorptivity and drying shrinkage. Correlations between compressive strength, modulus of elasticity and CBR are also established. Theoretical analysis of pavements incorporating subgrades improved by stabilized soils under traffic loads shows technical benefits compared with conventional flexible pavements without improved subgrades. Suitable stabilized soil mixtures using VA, L, cement and their combinations are proposed which can be used for the construction of road pavements, airfields, earth dams and low-cost housing. The use of locally available soils, VA and lime in the production of stabilized soils for such applications can provide sustainability for the local construction industry.
TL;DR: In this article, simultaneous GPS time-stamped measurements of the electric and magnetic fields at three distances and of the return stroke current associated with lightning strikes to the Toronto CN Tower (553 m) during the summer of 2005 are presented.
Abstract: [1] In this paper, simultaneous GPS time-stamped measurements of the electric and magnetic fields at three distances and of the return stroke current associated with lightning strikes to the Toronto CN Tower (553 m) during the summer of 2005 are presented. The lightning return stroke current was measured using a Rogowski coil installed at a height of 474 m above ground level (AGL). The vertical component of the electric field and the azimuthal component of the magnetic field were measured simultaneously at distances of 2.0 km, 16.8 km, and 50.9 km from the CN Tower. The propagation path from the CN Tower to the first two stations (2.0 and 16.8 km) was along the soil and through the Toronto city, whereas for the third location (50.9 km) the propagation path was nearly entirely across Lake Ontario. The waveforms of the electric and magnetic fields at 16.8 km and 50.9 km exhibit a first zero crossing about 5 μs after the onset of the return stroke. This early zero crossing is part of a narrow undershoot. For fields at 50.9 km the expected zero crossing at about 40 μs is also observed. Metallic beams and other conducting parts in buildings on which electric and magnetic field sensors were located cause an enhancement effect on the measured fields. Although an enhancement can be identified both on the electric and the magnetic fields, the degree of enhancement is actually more significant for the electric field than for the magnetic field. It is shown that the value of the wave impedance (E-field peak to H-field peak ratio) could give an estimate of the enhancement effect of the building on the electric field. Propagation effects (decrease of field amplitude and increase of its risetime) can also be observed in experimental records. It is shown that the fields at 50.9 km are less affected by such attenuation, compared to those at 16.8 km, presumably because the path of propagation is mostly across Lake Ontario. Measured waveforms are compared with theoretical predictions obtained using the five engineering return stroke models extended to include the presence of the strike object, namely, transmission line (TL), modified transmission line (MTLL and MTLE), Bruce-Golde (BG), and traveling current source (TCS) models. A reasonable agreement is found with all five engineering models for the magnetic field waveforms at the three considered distances, although the peak values of the computed fields are systematically about 25% lower than measured values. None of the models was able to reproduce the early zero crossing and the narrow undershoot. As far as the electric field is concerned, larger differences have been observed between simulations and measurements. This may be due to the fact that the enhancement effect of the building on the electric field is stronger than that on the magnetic field. The expression relating current and field peaks associated with strikes to tall structures is also tested versus obtained sets of experimental data. The overall agreement between the theoretically predicted and the experimentally observed field-to-current ratio is reasonable, although the formula of Bermudez et al. (2005) appears also to underestimate the experimentally measured ratio (by about 25%). This may be due, at least in part, to the enhancement effect of the buildings on which the field measurement antennae were installed.
TL;DR: It is concluded that the use of always-on mobile devices can lead to situations where conflict between work and personal activities is exacerbated rather than reduced.
Abstract: This paper presents a qualitative case study of Canadian BlackBerry® users. It begins with a brief description of the BlackBerry, a handheld wireless mobile e-mail device developed by Research in M...
TL;DR: In this paper, a novel switching sequence design for the space-vector modulation of high-power multilevel converters is presented, which is optimized for the improvement of harmonic spectrum and the minimization of device switching frequency.
Abstract: This paper presents a novel switching sequence design for the space-vector modulation of high-power multilevel converters. The switching sequences are optimized for the improvement of harmonic spectrum and the minimization of device switching frequency. Compared to other commonly used switching sequences, the output spectrum of the proposed design shows higher inverter equivalent switching frequency. Meanwhile, the device switching frequency is reduced by using a flexible switching pattern. The proposed switching sequence has been simulated and experimentally tested on a 5-level neutral point clamped H-bridge based inverter. The results from both simulations and experiments consistently verify the above-mentioned features.
TL;DR: An internationally recognized approach to returning childbirth to the remote Hudson coast communities of Nunavik, the Inuit region of Quebec, Canada is described, seen as a model of community-based education of Aboriginal midwives, integrating both traditional and modern approaches to care and education.
TL;DR: In this article, the authors investigated tourists' shopping-related beliefs and behaviors of craft souvenirs and segmented tourists into three groups: shopping enthusiasts, shopping lovers, and indifferent shoppers.