Showing papers by "Worcester Polytechnic Institute published in 2007"

WebQual: An Instrument for Consumer Evaluation of Web Sites

Abstract: Despite the critical need to know how consumers' perceptions of Web sites influence their behavior, and especially their intention to revisit or purchase, there is no extant general measure for evaluating Web sites and no consensus on what such an instrument should measure. The authors used the Theory of Reasoned Action and the Technology Acceptance Model to develop the WebQual instrument for consumer evaluation of Web sites. They refined it through a literature review and interviews with Web designers and users, and tested it using four samples of Web consumers. WebQual includes 12 dimensions (informational fit-to-task, tailored information, trust, response time, ease of understanding, intuitive operations, visual appeal, innovativeness, emotional appeal, consistent image, on-line completeness, relative advantage) and shows strong measurement validity. It is a highly validated instrument that can provide both wide- and fine-grained measurements of organizational Web sites.

Trojan Detection using IC Fingerprinting

Abstract: Hardware manufacturers are increasingly outsourcing their IC fabrication work overseas due to their much lower cost structure. This poses a significant security risk for ICs used for critical military and business applications. Attackers can exploit this loss of control to substitute Trojan ICs for genuine ones or insert a Trojan circuit into the design or mask used for fabrication. We show that a technique borrowed from side-channel cryptanalysis can be used to mitigate this problem. Our approach uses noise modeling to construct a set of fingerprints/or an IC family utilizing side- channel information such as power, temperature, and electromagnetic (EM) profiles. The set of fingerprints can be developed using a few ICs from a batch and only these ICs would have to be invasively tested to ensure that they were all authentic. The remaining ICs are verified using statistical tests against the fingerprints. We describe the theoretical framework and present preliminary experimental results to show that this approach is viable by presenting results obtained by using power simulations performed on representative circuits with several different Trojan circuitry. These results show that Trojans that are 3-4 orders of magnitude smaller than the main circuit can be detected by signal processing techniques. While scaling our technique to detect even smaller Trojans in complex ICs with tens or hundreds of millions of transistors would require certain modifications to the IC design process, our results provide a starting point to address this important problem.

Effects of Leading-Edge Protuberances on Airfoil Performance

Abstract: Lift, drag, and pitching moments of airfoils with leading-edge sinusoidal protuberances were measured in a water tunnel and compared with those of a baseline 63 4 -021 airfoil. The amplitude of the leading-edge protuberances ranged from 2.5 to 12% of the mean chord length; the spanwise wavelengths were 25 and 50% of the mean chord length. These ranges correspond to the morphology found on the leading edge of humpback whales' flippers. Flow visualization using tufts was also performed to examine the separation characteristics of the airfoils. For angles of attack less than the baseline stall angle, lift reduction and drag increase were observed for the modified foils. Above this angle, lift of the modified foils was up to 50% greater than the baseline foil with little or no drag penalty. The amplitude of the protuberances had a distinct effect on the performance of the airfoils, whereas the wavelength had little. Flow visualization indicated separated flow originating primarily from the troughs and attached flow on the peaks of the protuberances at angles beyond the stall angle of the baseline foil.

Technological Embeddedness and Organizational Change

Abstract: While various theories have been proposed to explain how technology leads to organizational change, in general they have focused either on the technology and ignored the influence of human agency, or on social interaction and ignored the technology. In this paper, we propose a new theory of technology-mediated organizational change that bridges these two extremes. Using grounded theory methodology, we conducted a three-year study of an enterprise system implementation. From the data collected, we identified embeddedness as central to the process of change. When embedded in technology, organizational elements such as routines and roles acquire a material aspect, in addition to the ostensive and performative aspects identified by Feldman and Pentland (2003). Our new theory employs the lens of critical realism because in our view, common constructivist perspectives such as structuration theory or actor network theory have limited our understanding of technology as a mediator of organizational change. Using a critical realist perspective, our theory explains the process of change as a three-stage cycle in which the ostensive, performative, and material aspects of organizational elements interact differently in each stage.

The structure and function of heavy metal transport P1B-ATPases.

Abstract: P(1B)-type ATPases transport heavy metals (Cu+, Cu2+, Zn2+, Co2+, Cd2+, Pb2+) across membranes Present in most organisms, they are key elements for metal homeostasis P(1B)-type ATPases contain 6-8 transmembrane fragments carrying signature sequences in segments flanking the large ATP binding cytoplasmic loop These sequences made possible the differentiation of at least four P(1B)-ATPase subgroups with distinct metal selectivity: P(1B-1): Cu+, P(1B-2): Zn2+, P(1B-3): Cu2+, P(1B-4): Co2+ Mutagenesis of the invariant transmembrane Cys in H6, Asn and Tyr in H7 and Met and Ser in H8 of the Archaeoglobus fulgidus Cu+-ATPase has revealed that their side chains likely coordinate the metals during transport and constitute a central unique component of these enzymes The structure of various cytoplasmic domains has been solved The overall structure of those involved in enzyme phosphorylation (P-domain), nucleotide binding (N-domain) and energy transduction (A-domain), appears similar to those described for the SERCA Ca2+-ATPase However, they show different features likely associated with singular functions of these proteins Many P(1B)-type ATPases, but not all of them, also contain a diverse arrangement of cytoplasmic metal binding domains (MBDs) In spite of their structural differences, all N- and C-terminal MBDs appear to control the enzyme turnover rate without affecting metal binding to transmembrane transport sites In addition, eukaryotic Cu+-ATPases have multiple N-MBD regions that participate in the metal dependent targeting and localization of these proteins The current knowledge of structure-function relationships among the different P(1B)-ATPases allows for a description of selectivity, regulation and transport mechanisms Moreover, it provides a framework to understand mutations in human Cu+-ATPases (ATP7A and ATP7B) that lead to Menkes and Wilson diseases

Mesenchymal stem cells support migration, extracellular matrix invasion, proliferation, and survival of endothelial cells in vitro.

Abstract: We investigated effects of the paracrine factors secreted by human mesenchymal stem cells (hMSCs) on endothelial cell migration, extracellular matrix invasion, proliferation, and survival in vitro. Human mesenchymal stem cells were cultured as a monolayer or as three-dimensional aggregates in hanging drops (hMSC spheroids). We performed analysis of paracrine factors in medium conditioned by a monolayer of hMSCs and hMSC spheroids. Concentrations of vascular endothelial growth factor (VEGF), basic fibroblast growth factor, angiogenin, procathepsin B, interleukin (IL)-11, and bone morphogenic protein 2 were increased 5-20 times in medium conditioned by hMSC spheroids, whereas concentrations of IL-6, IL-8, and monocyte hemoattractant protein-1 were not increased. Concentrations of VEGF and angiogenin in medium conditioned by hMSC spheroids showed a weak dependence on the presence of serum, which allows serum-free conditioned medium with elevated concentrations of angiogenic cytokines to be obtained. Medium conditioned by hMSC spheroids was more effective in stimulation of umbilical vein endothelial cell proliferation, migration, and basement membrane invasion than medium conditioned by a monolayer of hMSCs. This medium also promotes endothelial cell survival in vitro. We suggest that culturing of hMSCs as three-dimensional cellular aggregates provides a method to concentrate proangiogenic factors secreted by hMSCs and allows for reduction of serum concentration in conditioned medium. Our data support the hypothesis that hMSCs serve as trophic mediators for endothelial cells. Disclosure of potential conflicts of interest is found at the end of this article.

The process of technological competence leveraging

Abstract: Technologies are often amenable to uses for a range of markets, but yet are often underutilized, and consequently not all value is extracted from them. This article presents a longitudinal case study of a firm that successfully applied a fungible technology to products for its served market, but was unable to tap its considerable potential in new markets. The processes of resource allocation and resource transformation inhibited technology leveraging, shaped by the presence of a competence to serve current customers (a customer competence trap) and the lack of a competence to gain access to new customers (a marketing competence gap). Copyright © 2007 John Wiley & Sons, Ltd.

Finding Fluorescent Needles in the Cardiac Haystack: Tracking Human Mesenchymal Stem Cells Labeled with Quantum Dots for Quantitative In Vivo Three‐Dimensional Fluorescence Analysis

Abstract: Stem cells show promise for repair of damaged cardiac tissue. Little is known with certainty, however, about the distribution of these cells once introduced in vivo. Previous attempts at tracking delivered stem cells have been hampered by the autofluorescence of host tissue and limitations of existing labeling techniques. We have developed a novel loading approach to stably label human mesenchymal stem cells with quantum dot (QD) nanoparticles. We report the optimization and validation of this long-term tracking technique and highlight several important biological applications by delivering labeled cells to the mammalian heart. The bright QD crystals illuminate exogenous stem cells in histologic sections for at least 8 weeks following delivery and permit, for the first time, the complete three-dimensional reconstruction of the locations of all stem cells following injection into the heart. Disclosure of potential conflicts of interest is found at the end of this article.

On Broadcast Authentication in Wireless Sensor Networks

Abstract: Broadcast authentication is a critical security service in wireless sensor networks (WSNs), since it enables users to broadcast the WSN in an authenticated way. Symmetric key based schemes such as muTESLA and multilevel muTESLA have been proposed to provide such services for WSNs; however, these schemes all suffer from serious DoS attacks due to the delay in message authentication. This paper presents several effective public key based schemes to achieve immediate broadcast authentication and thus overcome the vulnerability presented in the muTESLA-like schemes. Several cryptographic techniques, including Merkle hash tree and identity-based signature scheme, are adopted to minimize the scheme overhead regarding the costs on both computation and communication. A quantitative energy consumption analysis of the proposed schemes is given in detail. We believe that this paper can serve as the start point towards fully solving the important multisender broadcast authentication problem in WSNs.

Some models and measures for evaluating performances with DEA: past accomplishments and future prospects

Abstract: This paper covers some of the past accomplishments of DEA (Data Envelopment Analysis) and some of its future prospects. It starts with the “engineering-science” definitions of efficiency and uses the duality theory of linear programming to show how, in DEA, they can be related to the Pareto–Koopmans definitions used in “welfare economics” as well as in the economic theory of production. Some of the models that have now been developed for implementing these concepts are then described and properties of these models and the associated measures of efficiency are examined for weaknesses and strengths along with measures of distance that may be used to determine their optimal values. Relations between the models are also demonstrated en route to delineating paths for future developments. These include extensions to different objectives such as “satisfactory” versus “full” (or “strong”) efficiency. They also include extensions from “efficiency” to “effectiveness” evaluations of performances as well as extensions to evaluate social-economic performances of countries and other entities where “inputs” and “outputs” give way to other categories in which increases and decreases are located in the numerator or denominator of the ratio (=engineering-science) definition of efficiency in a manner analogous to the way output (in the numerator) and input (in the denominator) are usually positioned in the fractional programming form of DEA. Beginnings in each of these extensions are noted and the role of applications in bringing further possibilities to the fore is highlighted.

Evidence of artemisinin production from IPP stemming from both the mevalonate and the nonmevalonate pathways.

Abstract: The potent antimalarial sesquiterpene lactone, artemisinin, is produced in low quantities by the plant Artemisia annua L. The source and regulation of the isopentenyl diphosphate (IPP) used in the biosynthesis of artemisinin has not been completely characterized. Terpenoid biosynthesis occurs in plants via two IPP-generating pathways: the mevalonate pathway in the cytosol, and the non-mevalonate pathway in plastids. Using inhibitors specific to each pathway, it is possible to resolve which supplies the IPP precursor to the end product. Here, we show the effects of inhibition on the two pathways leading to IPP for artemisinin production in plants. We grew young (7-14 days post cotyledon) plants in liquid culture, and added mevinolin to the medium to inhibit the mevalonate pathway, or fosmidomycin to inhibit the non-mevalonate pathway. Artemisinin levels were measured after 7-14 days incubation, and production was significantly reduced by each inhibitor compared to controls, thus, it appears that IPP from both pathways is used in artemisinin production. Also when grown in miconazole, an inhibitor of sterol biosynthesis, there was a significant increase in artemisinin compared to controls suggesting that carbon was shifted from sterols into sesquiterpenes. Collectively these results indicate that artemisinin is probably biosynthesized from IPP pools from both the plastid and the cytosol, and that carbon from competing pathways can be channeled toward sesquiterpenes. This information will help advance our understanding of the regulation of in planta production of artemisinin.

Crosslinking of discrete self-assembled collagen threads: Effects on mechanical strength and cell–matrix interactions

Abstract: Bundles of threads extruded from type I collagen have been researched extensively as scaffolds to promote the repair and regeneration of torn tendons and ligaments. The success of these scaffolds has been limited by insufficient tissue ingrowth from the wound margin, which may be inhibited by the chemical or physical crosslinking treatment used to increase the mechanical properties and decrease the degradation rate of these scaffolds. Recently, self-assembled collagen threads extruded from solutions of type I collagen molecules were shown to possess ultimate tensile strengths and structural properties comparable to native tendon fibers; however the tissue response to these threads has yet to be determined. The goal of this study was to investigate the effects of various crosslinking techniques on the mechanical properties as well as the in vitro rate of new tissue ingrowth on these threads. Our findings indicate that the physical crosslinking techniques, dehydrothermal (DHT) or ultraviolet light (UV), most significantly improve the mechanical strengths of the threads, but most significantly decrease the rate of cell migration. In contrast, carbodiimide (EDC) crosslinking achieved sub-optimal strength generation, but demonstrated improved cell migration rates. Future studies will investigate the design of threads with surface biochemistries that maximize tissue ingrowth while maintaining the mechanical stability of the scaffold.

A secure incentive protocol for mobile ad hoc networks

Abstract: The proper functioning of mobile ad hoc networks depends on the hypothesis that each individual node is ready to forward packets for others. This common assumption, however, might be undermined by the existence of selfish users who are reluctant to act as packet relays in order to save their own resources. Such non-cooperative behavior would cause the sharp degradation of network throughput. To address this problem, we propose a credit-based Secure Incentive Protocol (SIP) to stimulate cooperation among mobile nodes with individual interests. SIP can be implemented in a fully distributed way and does not require any pre-deployed infrastructure. In addition, SIP is immune to a wide range of attacks and is of low communication overhead by using a Bloom filter. Detailed simulation studies have confirmed the efficacy and efficiency of SIP.

Bead-to-fiber transition in electrospun polystyrene

Abstract: The morphological transition, namely bead-to-fiber transition, of electrospun polymer was examined for polystyrene, with its molecular weight ranging from 19,300 to 1,877,000 g/mol. Tetrahydrofuran and N,N-dimethylformamide were used as solvents to examine the effects of solvent properties on the morphological variations. Polymer molecular weight and solvent properties had a significant effect on the morphology of beads as well as fibers. Observation of fiber diameter and its distribution suggested that the effect of molecular weight and solvent may be independent. The critical concentrations at which incipient and complete fibers were observed were found to decrease significantly with molecular weight, as can be expected. The effect of solvents on these critical concentrations was minimal for moderate to high-molecular-weight (>100,000 g/mol) solutions. For low-molecular-weight solutions, the transition occurred at concentrations much lower than those predicted by a model, based exclusively on chain entanglements. Rapid solidification of jet which is expected to occur with concentrated solutions may play a vital role in establishing stable fibers during electrospinning. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007

On frame rate and player performance in first person shooter games

Abstract: The rate at which frames are rendered in a computer game directly impacts player performance, influencing both the game playability and enjoyability. However, despite the importance of frame rate and the wide-spread popularity of computer games, to the best of our knowledge, there is little quantitative understanding of the effects of frame rate on player performance in computer games. This paper provides a unique classification of actions in First Person Shooter (FPS) games based on interaction requirements that allow qualitative assessment of the impact of frame rates on player performance. This qualitative assessment is supported by quantitative analysis from two large user studies that measure the effects of frame rate on the fundamental player actions in a FPS game. Nearly 100 users participated in the two user study experiments, providing performance and perception data over a range of frame rates commonly studied for video streaming and inclusive of frame rates found in many computer game platforms. In general, the analysis shows that actions that require precise, rapid response, such as shooting, are greatly impacted by degradations in frame rates, while actions with lower precision and response requirements, such as moving, are more tolerant of low frame rates. These insights into the effects of frame rates on player performance can guide players in their choice for game settings and new hardware purchases, and inform system designers in their development of new hardware.

Measuring privacy loss and the impact of privacy protection in web browsing

Abstract: Various bits of information about users accessing Web sites. some of which are private, have been gathered since the inception of the Web. Increasingly the gathering, aggregation, and processing has been outsourced to third parties. The goal of this work is to examine the effectiveness of specific techniques to limit this diffusion of private information to third parties. We also examine the impact of these privacy protection techniques on the usability and quality of the Web pages returned. Using objective measures for privacy protection and page quality we examine their tradeoffs for different privacy protection techniques applied to a collection of popular Web sites as well as a focused set of sites with significant privacy concerns. We study privacy protection both at a browser and at a proxy.

Transistorlike behavior of a Bose-Einstein condensate in a triple-well potential

Abstract: In the last several years considerable efforts have been devoted to developing Bose-Einstein-condensate-based devices for applications such as fundamental research, precision measurements, and integrated atom optics. Such devices, capable of complex functionality, can be designed from simpler building blocks as is done in microelectronics. One of the most important components of microelectronics is a transistor. We demonstrate that a Bose-Einstein condensate in a three-well potential structure where the tunneling of atoms between two wells is controlled by the population in the third shows behavior similar to that of an electronic field-effect transistor. Namely, it exhibits switching and both absolute and differential gain. The role of quantum fluctuations is analyzed, and estimates of the switching time and parameters for the potential are presented.

On throughput efficiency of geographic opportunistic routing in multihop wireless networks

Abstract: Geographic opportunistic routing (GOR) is a new routing concept in multihop wireless networks. In stead of picking one node to forward a packet to, GOR forwards a packet to a set of candidate nodes and one node is selected dynamically as the actual forwarder based on the instantaneous wireless channel condition and node position and availability at the time of transmission. GOR takes advantages of the spatial diversity and broadcast nature of wireless communications and is an efficient mechanism to combat the unreliable links. The existing GOR schemes typically involve as many as available next-hop neighbors into the local opportunistic forwarding, and give the nodes closer to the destination higher relay priorities. In this paper, we focus on realizing GOR's potential in maximizing throughput. We start with an insightful analysis of various factors and their impact on the throughput of GOR, and propose a local metric named expected one-hop throughput (EOT) to balance the tradeoff between the benefit (i.e., packet advancement and transmission reliability) and the cost (i.e., medium time delay). We identify an upper bound of EOT and proof its concavity. Based on the EOT, we also propose a local candidate selection and prioritization algorithm. Simulation results validate our analysis and show that the metric EOT leads to both higher one-hop and path throughput than the corresponding pure GOR and geographic routing.

City-Regions and Social Reproduction: A ‘Place’ for Sustainable Development?

Abstract: Recent studies have suggested a city-region’s competitiveness is based not only on production, but social reproduction. These issues as well as the policy measures adopted by many city-regions are frequently couched in a discourse of ‘sustainable development’. But as an analytical framework how well does the concept of sustainable development account for the dynamics of social reproduction and the sustainability of a city-region? This article examines the possible relationship between city-regions and sustainable development at a conceptual level. We argue that despite some excellent work on the concept of ‘just sustainability’, current constructions of sustainable development are inadequate to capture the broad array of social and economic issues found in the city-region. As a way forward we initiate a discussion between the sustainability literature and labor geography, and provide a case study of a hospital privatization process in Boston, USA, which has been framed by a politics of city-regionalism.

Atomic Force Microscopy Study of the Effect of Lipopolysaccharides and Extracellular Polymers on Adhesion of Pseudomonas aeruginosa

Abstract: The roles of lipopolysaccharides (LPS) and extracellular polymers (ECP) on the adhesion of Pseudomonas aeruginosa PAO1 (expresses the A-band and B-band of O antigen) and AK1401 (expresses the A-band but not the B-band) to silicon were investigated with atomic force microscopy (AFM) and related to biopolymer physical properties. Measurement of macroscopic properties showed that strain AK1401 is more negatively charged and slightly more hydrophobic than strain PAO1 is. Microscopic AFM investigations of individual bacteria showed differences in how the biopolymers interacted with silicon. PAO1 showed larger decay lengths in AFM approach cycles, suggesting that the longer polymers on PAO1 caused greater steric repulsion with the AFM tip. For both bacterial strains, the long-range interactions we observed (hundreds of nanometers) were inconsistent with the small sizes of LPS, suggesting that they were also influenced by ECP, especially polysaccharides. The AFM retraction profiles provide information on the adhesion strength of the biopolymers to silicon (F(adh)). For AK1401, the adhesion forces were only slightly lower (F(adh) = 0.51 nN compared to 0.56 nN for PAO1), but the adhesion events were concentrated over shorter distances. More than 90% of adhesion events for AK1401 were at distances of 50% of adhesion events for PAO1 were at distances of >600 nm. The sizes of the observed molecules suggest that the adhesion of P. aeruginosa to silicon was controlled by ECP, in addition to LPS. Steric and electrostatic forces each contributed to the interfacial interactions between P. aeruginosa and the silicon surface.