Showing papers by "Worcester Polytechnic Institute published in 2005"

Dental microwear texture analysis shows within-species diet variability in fossil hominins

Abstract: Reconstructing the diets of extinct hominins is essential to understanding the paleobiology and evolutionary history of our lineage. Dental microwear, the study of microscopic tooth-wear resulting from use, provides direct evidence of what an individual ate in the past. Unfortunately, established methods of studying microwear are plagued with low repeatability and high observer error. Here we apply an objective, repeatable approach for studying three-dimensional microwear surface texture to extinct South African hominins. Scanning confocal microscopy together with scale-sensitive fractal analysis are used to characterize the complexity and anisotropy of microwear. Results for living primates show that this approach can distinguish among diets characterized by different fracture properties. When applied to hominins, microwear texture analysis indicates that Australopithecus africanus microwear is more anisotropic, but also more variable in anisotropy than Paranthropus robustus. This latter species has more complex microwear textures, but is also more variable in complexity than A. africanus. This suggests that A. africanus ate more tough foods and P. robustus consumed more hard and brittle items, but that both had variable and overlapping diets.

Taxonomy of XML schema languages using formal language theory

Abstract: On the basis of regular tree grammars, we present a formal framework for XML schema languages. This framework helps to describe, compare, and implement such schema languages in a rigorous manner. Our main results are as follows: (1) a simple framework to study three classes of tree languages (local, single-type, and regular); (2) classification and comparison of schema languages (DTD, W3C XML Schema, and RELAX NG) based on these classes; (3) efficient document validation algorithms for these classes; and (4) other grammatical concepts and advanced validation algorithms relevant to an XML model (e.g., binarization, derivative-based validation).

Verification and change-impact analysis of access-control policies

Abstract: Sensitive data are increasingly available on-line through the Web and other distributed protocols. This heightens the need to carefully control access to data. Control means not only preventing the leakage of data but also permitting access to necessary information. Indeed, the same datum is often treated differently depending on context. System designers create policies to express conditions on the access to data. To reduce source clutter and improve maintenance, developers increasingly use domain-specific, declarative languages to express these policies. In turn, administrators need to analyze policies relative to properties, and to understand the effect of policy changes even in the absence of properties. This paper presents Margrave, a software suite for analyzing role-based access-control policies. Margrave includes a verifier that analyzes policies written in the XACML language, translating them into a form of decision-diagram to answer queries. It also provides semantic differencing information between versions of policies. We have implemented these techniques and applied them to policies from a working software application.

Thermodynamics and Proton Transport in Nafion: II. Proton Diffusion Mechanisms and Conductivity

Abstract: A comprehensive pore transport model is proposed to describe proton diffusion within Nafion at various hydration levels by incorporating effects of water uptake and various proton transport mechanisms, namely, proton hopping along surface, Grotthuss diffusion, and ordinary mass diffusion of hydronium ions. The diffusion coefficients are predicted within a general random walk framework. The proton conductivity in contact with water vapor is accurately predicted as a function of relative humidity without any fitted parameters, considering the sorption isotherm proposed in the companion paper (Part I). A maximum conductivity in contact with liquid water is also predicted by the model for equivalent weight between 900 and 1000, in good agreement with the experimental measurements. The modeling framework could be extended to other proton conducting electrolytes for fuel cell applications. © 2005 The Electrochemical Society. All rights reserved.

Finding Form: Looking at the Field of Organizational Aesthetics

Abstract: Organizational research has long focused on the instrumental sphere with its questions of efficiency and effectiveness and in recent decades there has been interest in the moral sphere with its questions of ethics. Within the last decade there has also emerged a field that draws on the aesthetic sphere of our existence in organizations. In this review we look at the field of organizational aesthetics in terms of content and method, suggesting four broad categories of organizational aesthetics research: intellectual analysis of instrumental issues, artistic form used to look at instrumental issues, intellectual analysis of aesthetic issues, and artistic form used to look at aesthetic issues. We then suggest how organizational scholars might pursue artistic aesthetic organizational research.

Anonymous communications in mobile ad hoc networks

Abstract: Due to the broadcast nature of radio transmissions, communications in mobile ad hoc networks (MANETs) are more susceptible to malicious traffic analysis. In this paper we propose a novel anonymous on-demand routing protocol, termed MASK, to enable anonymous communications thereby thwarting possible traffic analysis attacks. Based on a new cryptographic concept called pairing, we first propose an anonymous neighborhood authentication protocol which allows neighboring nodes to authenticate each other without revealing their identities. Then utilizing the secret pairwise link identifiers and keys established between neighbors during the neighborhood authentication process, MASK fulfills the routing and packet forwarding tasks nicely without disclosing the identities of participating nodes under a rather strong adversarial model. MASK provides the desirable sender and receiver anonymity, as well as the relationship anonymity of the sender and receiver. It is also resistant to a wide range of adversarial attacks. Moreover, MASK preserves the routing efficiency in contrast to previous proposals. Detailed anonymity analysis and simulation studies are carried out to validate and justify the effectiveness of MASK.

Thermodynamics and Proton Transport in Nafion I. Membrane Swelling, Sorption, and Ion-Exchange Equilibrium

Abstract: A thermodynamic model is proposed to describe the sorption of water in Nafion based on the Flory-Huggins activity model and an appropriate osmotic pressure correction term for the chemical potential of water within the swollen membrane. The key variables for sorption are equivalent weight of ionomer, acid strength of the ionic groups, modulus of polymer elasticity, and interaction between water and polymer. The water uptake per unit mass of dry Nafion increases with the increasing acid strength of the functional groups, decreasing Young’s modulus, and decreasing equivalent weight of Nafion. The model provides insights into the sorption and swelling behavior of ion-exchange membranes, and thus, may be useful in evaluating and designing alternate proton-exchange membranes for fuel cell applications. In a companion paper ~Part II!, a predictive model is presented for the transport of protons in Nafion.

Dense Perovskite, La1-xA′xFe1-yCoyO3-δ (A′= Ba, Sr, Ca), Membrane Synthesis, Applications, and Characterization

Abstract: La1-xA′xFe0.8Co0.2O3-δ (A′= Ca, Sr, Ba) perovskite powders were synthesized to attain the desired properties of high O2 flux and stability under reducing conditions. Steady-state oxygen permeation rates for La1-xA′xFe0.8-Co0.2O3-δ perovskite membranes in nonreacting experiments with air on one side and helium on the other side of the membrane were in the order A′x= Ba0.8 > Ba0.6 > Ca0.6 > Sr0.6. Partial oxidation of methane to syngas (CO + H2) was performed in a dense La0.2Ba0.8Fe0.8Co0.2O3-δ membrane reactor at 850°C in which oxygen was separated from air and simultaneously fed into the methane stream. The reducing atmosphere affected the membrane reaction-side surface while barium enrichment occurred on the air-side surface. Oxygen continuously transported from the air side appeared to stabilize the membrane interior, and the reactor was operated for up to 850 h.

Understanding enterprise systems-enabled integration

Abstract: A key touted benefit of enterprise systems (ES) is organizational integration of both business processes and data, which is expected to reduce processing time and increase control over operations. In our 3-year longitudinal case study of a phased ES implementation, we employed a grounded theory methodology to discover organizational effects of ES. As we coded and analyzed our field data, we observed many integration effects. Further analysis revealed underlying dimensions of ES-enabled integration. ES-enabled integration varied depending on the relationship between the integrated business units (similar plants, stages in a business process, or dissimilar functional areas) and on whether processes or data were integrated. Turning to the literature, we realized that Thompson's three types of interdependence, pooled, sequential, and reciprocal, captured the business relationships revealed in our data. Thus, we describe the salient characteristics of ES-enabled integration using Thompson's interdependence types applied to process and data integration. We also identify dimensions of differentiation between business units that contribute to integration problems. Viewing our field data through the lens of these salient characteristics and dimensions of differentiation provided theoretical explanations for observed integration problems. These findings also help managers understand and anticipate ES-enabled integration opportunities and problems.

Teaching software engineering through game design

Abstract: Many projects currently used in Software Engineering curricula lack both the "fun factor" needed to engage students, as well as the practical realism of engineering projects that include other computer science disciplines such as Software Engineering, Networks, or Human Computer Interaction. This paper reports on our endeavor to enhance interest and retention in an existing Software Engineering curriculum through the use of computer game-based projects. Specifically, a set of game-centric, project-based modules have been developed that enable students to: (1) actively participate in the different phases of the software lifecycle taking a single project from requirement elicitation to testing and maintenance; (2) expose students to real issues in project and team management over the course of a 2-semester project; and at the same time (3) introduce students to the different aspects of computer game design. Preliminary results suggest the merits of our approach, showing improved class participation and performance.

A slack-based measure of efficiency in context-dependent data envelopment analysis

Abstract: Data envelopment analysis (DEA) has been proven as an excellent data-oriented performance evaluation method when multiple inputs and outputs are present in a set of peer decision-making units (DMUs). In the DEA literature, a context-dependent DEA is developed to provide finer evaluation results by examining the efficiency of DMUs in specific performance levels based upon radial DEA efficiency scores. In DEA, non-zero input and output slacks are very likely to present after the radial efficiency score improvement. Often, these non-zero slack values represent a substantial amount of inefficiency. Therefore, in order to fully measure the inefficiency in DMU's performance, it is very important to also consider the inefficiency represented by the non-zero slacks in the context-dependent DEA. This study proposes a slack-based context-dependent DEA which allows a full evaluation of inefficiency in a DMUs performance. By using slack-based efficiency measure, we obtain different frontier levels and more appropriate performance benchmarks for inefficient DMUs.

Local maximal stress hypothesis and computational plaque vulnerability index for atherosclerotic plaque assessment.

Abstract: It is believed that atherosclerotic plaque rupture may be related to maximal stress conditions in the plaque. More careful examination of stress distributions in plaques reveals that it may be the local stress/strain behaviors at critical sites such as very thin plaque cap and locations with plaque cap weakness that are more closely related to plaque rupture risk. A “local maximal stress hypothesis” and a stress-based computational plaque vulnerability index (CPVI) are proposed to assess plaque vulnerability. A critical site selection (CSS) method is proposed to identify critical sites in the plaque and critical stress conditions which are be used to determine CPVI values. Our initial results based on 34 2D MRI slices from 14 human coronary plaque samples indicate that CPVI plaque assessment has an 85% agreement rate (91% if the square root of stress values is used) with assessment given by histopathological analysis. Large-scale and long-term patient studies are needed to further validate our findings for more accurate quantitative plaque vulnerability assessment.

In the Name of the Practical: Unearthing the Hegemony of Pragmatics in the Discourse of Environmental Management*

Abstract: A prominent feature of the rapidly growing field of EnvironmentalManagement (EM) is its strong emphasis on pragmatic considerations. Much of EM’slegitimacy stems from its own identity as having practical relevance in resolvingcontemporary environmental problems. With the help of Critical Discourse Analysis,our paper engages closely with the language of practicality in EnvironmentalManagement. We show how the message of practicality emerged through three coremessages in the discourse, viz. economic utilitarianism, compromise and inter-organizational collaboration. We further contend that in the actual material contextof the complex biospheric environment, these messages may have less than pragmaticimplications. We conclude with a discussion of ecological rationality in redefining thediscourse of pragmatics in Environmental Management. INTRODUCTION Practical men, who believe themselves to be quite exempt from any intellectualinfluences, are usually the slaves of some defunct economist. ( John MaynardKeynes,

A Stream Function Method for Gradient Coil Design

Abstract: A new design approach for the construction of gradient coils for magnetic resonance imaging is presented The theoretical formulation involves a constraint cost function between the desired field in a particular region of interest in space and an almost arbitrarily defined surface that carries the current configuration based on Biot-Savart's integral equation An appropriate weight function in conjunction with linear approximation functions permits the transformation of the problem formulation into a linear matrix equation whose solution yields discrete current elements in terms of magnitude and direction within a specified coil surface Numerical predictions and comparisons with practical measurements for the Gx ,G y ,G z gradient coils underscore the success of this approach in terms of achieving highly linear fields while maintaining low parasitic fields and low inductances © 2005 Wiley Periodicals, Inc

Quantifying Effects of Plaque Structure and Material Properties on Stress Distributions in Human Atherosclerotic Plaques Using 3D FSI Models

Abstract: Background Atherosclerotic plaques may rupture without warning and cause acute cardiovascular syndromes such as heart attack and stroke. Methods to assess plaque vulnerability noninvasively and predict possible plaque rupture are urgently needed.

The apparent power concept and the IEEE standard 1459-2000

Abstract: This paper rigorously considers the concept of apparent power in unbalanced three-phase situations. The analysis shows that there are various related but different concepts that can be associated with the apparent power. In particular two approaches are covered, the one relating to the literature on the single-phase sinusoidal case, the other relating to the recent IEEE Standard 1459-2000. The underlying ideas for each concept are given; the relationship and the differences between them are thoroughly discussed.

Microstructure of cell wall-associated melanin in the human pathogenic fungus Cryptococcus neoformans

Abstract: Melanin is a virulence factor for many pathogenic fungal species, including Cryptococcus neoformans. Melanin is deposited in the cell wall, and melanin isolated from this fungus retains the shape of the cells, resulting in hollow spheres called "ghosts". In this study, atomic force, scanning electron, and transmission electron microscopy revealed that melanin ghosts are covered with roughly spherical granular particles approximately 40-130 nm in diameter, and that the melanin is arranged in multiple concentric layers. Nuclear magnetic resonance cryoporometry indicated melanin ghosts contain pores with diameters between 1 and 4 nm, in addition to a small number of pores with diameters near 30 nm. Binding of the antibodies to melanin reduced the apparent measured volume of these pores, suggesting a mechanism for their antifungal effect. We propose a model of cryptococcal melanin structure whereby the melanin granules are held together in layers. This structural model has implications for cell division, cell wall remodeling, and antifungal drug discovery.

The effect of phytohormones on growth and artemisinin production in artemisia annua hairy roots

Abstract: Few studies have focused on the effect of a broad range of phytohormones on growth and secondary metabolism of a single hairy root species. We measured growth, development, and production of the antimalarial drug, artemisinin, in Artemisia annua hairy roots in response to the five main hormones: auxins, cytokinins, ethylene, gibberellins (GA), and abscisic acid (ABA). Single roots grown in six-well plates in medium B5 with 0.01 mgl−1 (0.029 μM) GA3 produced the highest values overall in terms of the number of lateral roots, length of the primary root, lateral root tip density, total lateral root length, and total root length. When the total root lengths are compared, the best conditions for stimulating elongation appear to be: GA 0.01 mgl−1 (0.029μM)> ABA 1.0 mgl−1 (3.78μM)=GA 0.02 mgl−1 (0.058μM). Bulk yields of biomass were inversely proportional to the concentration of each hormone tested. All cultures provided with ABA yielded the highest amount of biomass. Both 6-benzylaminopurine and 2-isopentenyladenine inhibited root growth, however, only 2-isopentenyladenine stimulated artemisinin production, more than twice that of the B5 controls, and more than any other hormone studied. These results will prove useful in increasing hairy root growth and artemisinin production.

System and method to increase network throughput

Abstract: Data flows in a network are managed by dynamically determining bandwidth usage and available bandwidth for IP-ABR service data flows and dynamically allocating a portion of the available bandwidth to the IP-ABR data flows. Respective bandwidth requests from network hosts are received and an optimal window size for a sender host is determined based upon bandwidth allocated for the data flow and a round trip time of a segment to provide self-pacing of the data flow.