Showing papers by "Purdue University published in 2003"

Ballistic carbon nanotube field-effect transistors

Abstract: A common feature of the single-walled carbon-nanotube field-effect transistors fabricated to date has been the presence of a Schottky barrier at the nanotube–metal junctions1,2,3. These energy barriers severely limit transistor conductance in the ‘ON’ state, and reduce the current delivery capability—a key determinant of device performance. Here we show that contacting semiconducting single-walled nanotubes by palladium, a noble metal with high work function and good wetting interactions with nanotubes, greatly reduces or eliminates the barriers for transport through the valence band of nanotubes. In situ modification of the electrode work function by hydrogen is carried out to shed light on the nature of the contacts. With Pd contacts, the ‘ON’ states of semiconducting nanotubes can behave like ohmically contacted ballistic metallic tubes, exhibiting room-temperature conductance near the ballistic transport limit of 4e2/h (refs 4–6), high current-carrying capability (∼25 µA per tube), and Fabry–Perot interferences5 at low temperatures. Under high voltage operation, the current saturation appears to be set by backscattering of the charge carriers by optical phonons. High-performance ballistic nanotube field-effect transistors with zero or slightly negative Schottky barriers are thus realized.

Time-Frequency Analysis

Abstract: Conventionally, time series have been studied either in the time domain or the frequency domain. The representation of a signal in the time domain is localized in time, i.e. the value of the signal at each instant in time is well defined. However, the time representation of a signal is poorly localized in frequency, i.e. little information about the frequency content of the signal at a certain frequency can be known by looking at the signal in the time domain. On the other hand, the representation of a signal in the frequency domain is well localized in frequency, but is poorly localized in time, and as a consequence it is impossible to tell when certain events occurred in time.

Leakage current mechanisms and leakage reduction techniques in deep-submicrometer CMOS circuits

Abstract: High leakage current in deep-submicrometer regimes is becoming a significant contributor to power dissipation of CMOS circuits as threshold voltage, channel length, and gate oxide thickness are reduced. Consequently, the identification and modeling of different leakage components is very important for estimation and reduction of leakage power, especially for low-power applications. This paper reviews various transistor intrinsic leakage mechanisms, including weak inversion, drain-induced barrier lowering, gate-induced drain leakage, and gate oxide tunneling. Channel engineering techniques including retrograde well and halo doping are explained as means to manage short-channel effects for continuous scaling of CMOS devices. Finally, the paper explores different circuit techniques to reduce the leakage power consumption.

An energy efficient hierarchical clustering algorithm for wireless sensor networks

Abstract: A wireless network consisting of a large number of small sensors with low-power transceivers can be an effective tool for gathering data in a variety of environments. The data collected by each sensor is communicated through the network to a single processing center that uses all reported data to determine characteristics of the environment or detect an event. The communication or message passing process must be designed to conserve the limited energy resources of the sensors. Clustering sensors into groups, so that sensors communicate information only to clusterheads and then the clusterheads communicate the aggregated information to the processing center, may save energy. In this paper, we propose a distributed, randomized clustering algorithm to organize the sensors in a wireless sensor network into clusters. We then extend this algorithm to generate a hierarchy of clusterheads and observe that the energy savings increase with the number of levels in the hierarchy. Results in stochastic geometry are used to derive solutions for the values of parameters of our algorithm that minimize the total energy spent in the network when all sensors report data through the clusterheads to the processing center.

Algorithms in real algebraic geometry

Abstract: Algebraically Closed Fields- Real Closed Fields- Semi-Algebraic Sets- Algebra- Decomposition of Semi-Algebraic Sets- Elements of Topology- Quantitative Semi-algebraic Geometry- Complexity of Basic Algorithms- Cauchy Index and Applications- Real Roots- Cylindrical Decomposition Algorithm- Polynomial System Solving- Existential Theory of the Reals- Quantifier Elimination- Computing Roadmaps and Connected Components of Algebraic Sets- Computing Roadmaps and Connected Components of Semi-algebraic Sets

Agrobacterium-Mediated Plant Transformation: the Biology behind the “Gene-Jockeying” Tool

Abstract: Agrobacterium tumefaciens and related Agrobacterium species have been known as plant pathogens since the beginning of the 20th century. However, only in the past two decades has the ability of Agrobacterium to transfer DNA to plant cells been harnessed for the purposes of plant genetic engineering. Since the initial reports in the early 1980s using Agrobacterium to generate transgenic plants, scientists have attempted to improve this “natural genetic engineer” for biotechnology purposes. Some of these modifications have resulted in extending the host range of the bacterium to economically important crop species. However, in most instances, major improvements involved alterations in plant tissue culture transformation and regeneration conditions rather than manipulation of bacterial or host genes. Agrobacterium-mediated plant transformation is a highly complex and evolved process involving genetic determinants of both the bacterium and the host plant cell. In this article, I review some of the basic biology concerned with Agrobacterium-mediated genetic transformation. Knowledge of fundamental biological principles embracing both the host and the pathogen have been and will continue to be key to extending the utility of Agrobacterium for genetic engineering purposes.

A conceptual model of perceived customer value in e-commerce: A preliminary investigation

Abstract: This article presents an exploratory study of a conceptual model of perceived customer value in a business-to-consumer e-commerce setting Key precursors of perceived customer value included in the model are valence of on-line shopping experience, perceived product quality, perceived risk, and product price Relationships among these variables (as well as mediating variables) and their relationship to on-line shoppers' value perceptions are explored The theoretical framework proposed in this work expands on previous efforts on perceived customer value by including new variables relevant to an e-commerce setting and by integrating several key variables into one model The preliminary findings lead to several implications © 2003 Wiley Periodicals, Inc

Client Importance, Nonaudit Services, and Abnormal Accruals

Abstract: The economic theory of auditor independence (DeAngelo 1981b) suggests that auditors' incentives to compromise their independence are related to client importance. Using ratios of client fees and of nonaudit fees divided by the audit firm's U.S. revenues or a surrogate for the audit‐practice‐office revenues as measures of client importance, we investigate their association with Jones‐model abnormal accruals. In a sample of 1,871 clients of Big 5 audit firms we do not find a statistically significant association between abnormal accruals and any of the client importance measures. Our theory development also suggests that auditor incentives to compromise independence should increase with the extent of client opportunities and incentives to manage earnings, and decrease with the strength of corporate governance and auditor expertise. We also do not find a statistically significant association between abnormal accruals and client importance in subsets of the samples partitioned by proxies for these factors.

High-order entropy-compressed text indexes

Abstract: We present a novel implementation of compressed suffix arrays exhibiting new tradeoffs between search time and space occupancy for a given text (or sequence) of n symbols over an alphabet σ, where each symbol is encoded by lgvσv bits. We show that compressed suffix arrays use just nHh + σ bits, while retaining full text indexing functionalities, such as searching any pattern sequence of length m in O(m lg vσv + polylog(n)) time. The term Hh ≤ lg vσv denotes the hth-order empirical entropy of the text, which means that our index is nearly optimal in space apart from lower-order terms, achieving asymptotically the empirical entropy of the text (with a multiplicative constant 1). If the text is highly compressible so that Hn = o(1) and the alphabet size is small, we obtain a text index with o(m) search time that requires only o(n) bits. Further results and tradeoffs are reported in the paper.

Chandra X-Ray Spectroscopic Imaging of Sagittarius A* and the Central Parsec of the Galaxy

Abstract: We report the results of the first-epoch observation with the ACIS-I instrument on the Chandra X-Ray Observatory of Sagittarius A* (Sgr A*), the compact radio source associated with the supermassive black hole (SMBH) at the dynamical center of the Milky Way. This observation produced the first X-ray (0.5- 7 keV) spectroscopic image with arcsecond resolution of the central 17 0 � 17 0 (40 pc � 40 pc) of the Galaxy. We report the discovery of an X-ray source, CXOGC J174540.0� 290027, coincident with Sgr A* within 0>27 � 0>18. The probability of a false match is estimated to be d0.5%. The spectrum is well fitted either by an absorbed power law with photon index � � 2:7 or by an absorbed optically thin thermal plasma with kT � 1:9 keV and column density NH � 1 � 10 23 cm � 2 . The observed flux in the 2-10 keV band is � 1:3 � 10 � 13 ergs cm � 2 s � 1 , and the absorption-corrected luminosity is � 2:4 � 10 33 ergs s � 1 . The X-ray emission at the position of Sgr A* is extended, with an intrinsic size of � 1>4 (FWHM), consistent with the Bondi accretion radius for a 2:6 � 10 6 Mblack hole. A compact component within the source flared by up to a factor of 3 over a period of � 1 hr at the start of the observation. The search for Kline emission from iron was inconclusive, yielding an upper limit on the equivalent width of 2.2 keV. Several potential stellar origins for the X-ray emission at Sgr A* are considered, but we conclude that the various properties of the source favor accretion onto the SMBH as the origin for the bulk of the emission. These data are inconsistent with '' standard '' advection-dominated accretion flow (ADAF) models or Bondi models, unless the accretion rate from stellar winds is much lower than anticipated. The central parsec of the Galaxy contains an � 1.3 keV plasma with electron density ne � 26� � 1=2 f cm � 3 , wheref is the filling factor. This plasma should supply � 10 � 6 Myr � 1 of material to the accretion flow at the Bondi radius, whereas measurements of linear polar- ization at 150 GHz and above limit the accretion rate near the event horizon to d10 � 8 Myr � 1 , assuming an equipartition magnetic field. Taken together, the X-ray and radio results imply that outflows or convection are playing a role in ADAF models and subequipartition magnetic fields in Bondi models, or else the X-ray emission must be generated predominantly via the synchrotron self-Compton (SSC) process. The measured extent of the source and the detection of short timescale variability are evidence that the emission from Sgr A* contains both thermal and nonthermal emission components at comparable levels. We also discuss the complex structure of the X-ray emission from the Sgr A radio complex and along the Galactic plane. Mor- phological evidence is presented that Sgr A* and the H ii region Sgr A West lie within the hot plasma in the central cavity of Sgr A East, which we interpret as a supernova remnant that may have passed through the position of the SMBH, leading to a period of increased activity that ended within the past � 300 yr. Similarly, we have discovered bright clumps of X-ray emission located on opposite sides of the Galactic plane, along a line passing through the central parsec of the Galaxy. The arrangement of these lobes suggests that Sgr A* may have experienced an earlier period of increased activity lasting several thousand years during which it expelled hot gas in a bipolar outflow oriented roughly perpendicular to the Galactic plane. Additionally, we present an analysis of stellar emission within the central parsec of the Galaxy. Subject headings: accretion, accretion disks — black hole physics — galaxies: active — Galaxy: center — X-rays: ISM — X-rays: stars

Monetary and Non-Monetary Punishment in the Voluntary Contributions Mechanism

Abstract: A demand for behavioral norms arises when members of a group have individual incentives to take actions that reduce the group's overall welfare (James S. Coleman, 1990). Norms require enforcement with a system of sanctions that penalize deviations from acceptable behavior (George C. Homans, 1961). Formal sanctions include fines or restrictions implemented by a legal system or private individuals that impose costs of money and time on the offender. However, informal sanctions such as peer pressure, gossip, or social ostracism might in some cases also be effective deterrents, and expressions of social acceptance might be effective in encouraging group-oriented behavior (Peter M. Blau, 1964). Indeed, the fact that expressions of approval and disapproval are commonly observed in human interaction suggests that they must influence the behavior of at least some individuals. In recognition of the importance of informal sanctions, economists have integrated phenomena such as peer pressure (Eugene Kandel and Edward P. Lazear, 1992; John M. Barron and Kathy Paulson-Gjerde, 1997), and the avoidance of social disapproval (George A. Akerlof, 1980; Heinz Hollander, 1990; Assar Lindbeck et al., 1999) into theoretical models. Social pressures are thought to be a major factor behind high voter participation (Carol-Jean Uhlaner, 1989; Stephen Knack, 1992) and compliance with the law (Tom R. Tyler, 1990).

Theory of ballistic nanotransistors

Abstract: Numerical simulations are used to guide the development of a simple analytical theory for ballistic field-effect transistors. When two-dimensional (2-D) electrostatic effects are small (and when the insulator capacitance is much less than the semiconductor (quantum) capacitance), the model reduces to Natori's theory of the ballistic MOSFET. The model also treats 2-D electrostatics and the quantum capacitance limit where the semiconductor quantum capacitance is much less than the insulator capacitance. This new model provides insights into the performance of MOSFETs near the scaling limit and a unified framework for assessing and comparing a variety of novel transistors.

Structure of the Cytochrome b6f Complex of Oxygenic Photosynthesis: Tuning the Cavity

Abstract: The cytochrome b6f complex provides the electronic connection between the photosystem I and photosystem II reaction centers of oxygenic photosynthesis and generates a transmembrane electrochemical proton gradient for adenosine triphosphate synthesis. A 3.0 angstrom crystal structure of the dimeric b6f complex from the thermophilic cyanobacterium Mastigocladus laminosus reveals a large quinone exchange cavity, stabilized by lipid, in which plastoquinone, a quinone-analog inhibitor, and a novel heme are bound. The core of the b6f complex is similar to the analogous respiratory cytochrome bc1 complex, but the domain arrangement outside the core and the complement of prosthetic groups are strikingly different. The motion of the Rieske iron-sulfur protein extrinsic domain, essential for electron transfer, must also be different in the b6f complex.

Privacy-preserving k-means clustering over vertically partitioned data

Abstract: Privacy and security concerns can prevent sharing of data, derailing data mining projects. Distributed knowledge discovery, if done correctly, can alleviate this problem. The key is to obtain valid results, while providing guarantees on the (non)disclosure of data. We present a method for k-means clustering when different sites contain different attributes for a common set of entities. Each site learns the cluster of each entity, but learns nothing about the attributes at other sites.

Composing Web services on the Semantic Web

Abstract: Service composition is gaining momentum as the potential silver bullet for the envisioned Semantic Web. It purports to take the Web to unexplored efficiencies and provide a flexible approach for promoting all types of activities in tomorrow’s Web. Applications expected to heavily take advantage of Web service composition include B2B E-commerce and E-government. To date, enabling composite services has largely been an ad hoc, time-consuming, and error-prone process involving repetitive low-level programming. In this paper, we propose an ontology-based framework for the automatic composition of Web services. We present a technique to generate composite services from high-level declarative descriptions. We define formal safeguards for meaningful composition through the use of composability rules. These rules compare the syntactic and semantic features of Web services to determine whether two services are composable. We provide an implementation using an E-government application offering customized services to indigent citizens. Finally, we present an exhaustive performance experiment to assess the scalability of our approach.

Handbook of Communication and Social Interaction Skills

Abstract: Contents: J.M. Wiemann, Foreword. J.O. Greene, B.R. Burleson, Preface. Part I:General Theoretical and Methodological Issues. S.R. Wilson, C.M. Sabee, Explicating Communicative Competence as a Theoretical Term. J.O. Greene, Models of Adult Communication Skill Acquisition: Practice and the Course of Performance Improvement. B.H. Spitzberg, Methods of Interpersonal Skill Assessment. C. Segrin, M. Givertz, Methods of Social Skills Training and Development. Part II:Fundamental Interaction Skills. J.K. Burgoon, A.E. Bacue, Nonverbal Communication Skills. R.E. Sanders, Applying the Skills Concept to Discourse and Conversation: The Remediation of Performance Defects in Talk-in-Interaction. C.R. Berger, Message Production Skill in Social Interaction. R.S. Wyer, Jr., R. Adaval, Message Reception Skills in Social Communication. S. Metts, E. Grohskopf, Impression Management: Goals, Strategies, and Skills. Part III:Function-Focused Communication Skills. K.E. Rowan, Informing and Explaining Skills: Theory and Research on Informative Communication. D. Hample, Arguing Skill. J.P. Dillard, L.J. Marshall, Persuasion as a Social Skill. D.J. Canary, Managing Interpersonal Conflict: A Model of Events Related to Strategic Choices. B.R. Burleson, Emotional Support Skills. J. Mandelbaum, How to "Do Things" With Narrative: A Communication Perspective on Narrative Skill. Part IV:Skills in Close Personal Relationships. W. Samter, Friendship Interaction Skills Across the Life Span. K. Dindia, L. Timmerman, Accomplishing Romantic Relationships. A.B. Kelly, F.K. Fincham, S.R.H. Beach, Communication Skills in Couples: A Review and Discussion of Emerging Perspectives. C.H. Hart, L.D. Newell, S.F. Olsen, Parenting Skills and Social-Communicative Competence in Childhood. Part V:Skills in Public and Professional Contexts. M.E. Roloff, L.L. Putnam, L. Anastasiou, Negotiation Skills. D.S. Gouran, Communication Skills for Group Decision Making. J.A. Daly, A.L. Vangelisti, Skillfully Instructing Learners: How Communicators Effectively Convey Messages. R.L. Street, Jr., Interpersonal Communication Skills in Health Care Contexts. C. Hajek, H. Giles, New Directions in Intercultural Communication Competence: The Process Model.

Random projection for high dimensional data clustering: a cluster ensemble approach

Abstract: We investigate how random projection can best be used for clustering high dimensional data. Random projection has been shown to have promising theoretical properties. In practice, however, we find that it results in highly unstable clustering performance. Our solution is to use random projection in a cluster ensemble approach. Empirical results show that the proposed approach achieves better and more robust clustering performance compared to not only single runs of random projection/clustering but also clustering with PCA, a traditional data reduction method for high dimensional data. To gain insights into the performance improvement obtained by our ensemble method, we analyze and identify the influence of the quality and the diversity of the individual clustering solutions on the final ensemble performance.

Bread Staling: Molecular Basis and Control.

Abstract: The molecular basis of staling is examined by reviewing what is known about the components of wheat flour, factors that affect staling rate, and the various mechanisms that have been proposed. The conclusion reached is that bread staling is a complex phenomenon in which multiple mechanisms operate. Polymer crystallizations with the formation of supermolecular structures are certainly involved. The most plausible hypothesis is that retrogradation of amylopectin occurs, and because water molecules are incorporated into the crystallites, the distribution of water is shifted from gluten to starch/amylopectin, thereby changing the nature of the gluten network. The role of additives may be to change the nature of starch protein molecules, to function as plasticizers, and/or to retard the redistribution of water between components. Nothing more definite can be concluded at this time.

Evaluating probabilistic queries over imprecise data

Abstract: Many applications employ sensors for monitoring entities such as temperature and wind speed. A centralized database tracks these entities to enable query processing. Due to continuous changes in these values and limited resources (e.g., network bandwidth and battery power), it is often infeasible to store the exact values at all times. A similar situation exists for moving object environments that track the constantly changing locations of objects. In this environment, it is possible for database queries to produce incorrect or invalid results based upon old data. However, if the degree of error (or uncertainty) between the actual value and the database value is controlled, one can place more confidence in the answers to queries. More generally, query answers can be augmented with probabilistic estimates of the validity of the answers. In this paper we study probabilistic query evaluation based upon uncertain data. A classification of queries is made based upon the nature of the result set. For each class, we develop algorithms for computing probabilistic answers. We address the important issue of measuring the quality of the answers to these queries, and provide algorithms for efficiently pulling data from relevant sensors or moving objects in order to improve the quality of the executing queries. Extensive experiments are performed to examine the effectiveness of several data update policies.

Disappearance of back-to-back high-pT Hadron correlations in central Au + Au collisions at √SNN = 200 GeV

Abstract: Azimuthal correlations for large transverse momentum charged hadrons have been measured over a wide pseudorapidity range and full azimuth in Au+Au and p+p collisions at roots(NN)=200 GeV. The small-angle correlations observed in p+p collisions and at all centralities of Au+Au collisions are characteristic of hard-scattering processes previously observed in high-energy collisions. A strong back-to-back correlation exists for p+p and peripheral Au+Au. In contrast, the back-to-back correlations are reduced considerably in the most central Au+Au collisions, indicating substantial interaction as the hard-scattered partons or their fragmentation products traverse the medium.

Transverse momentum and collision energy dependence of high p(T) hadron suppression in Au+Au collisions at ultrarelativistic energies

Abstract: We report high statistics measurements of inclusive charged hadron production in Au+Au and p+p collisions at rootS(NN)=200 GeV. A large, approximately constant hadron suppression is observed in central Au+Au collisions for 5