Finding the number of clusters in ordered dissimilarities

As humans, we have innate faculties that allow us to efficiently segment groups of objects. Computers, to some degree, can be programmed with similar categorical capabilities, which stem from exploratory data analysis. Out of the various subsets of data reasoning, clustering provides insight into the structure and relationships of input samples situated in a number of distributions. To determine these relationships, many clustering methods rely on one or more human inputs; the most important being the number of distributions, c, to seek. This work investigates a technique for estimating the number of clusters from a general type of data called relational data. Several numerical examples are presented to illustrate the effectiveness of the proposed method.     

Utilizing Iron's Attractive Chemical and Magnetic Properties in Microrocket Design,Extended Motion,and Unique Performance

All‐in‐one material for microrocket propulsion featuring acid‐based bubble generation and magnetic guidance is presented. Electrochemically deposited iron serves as both a propellant, toward highly efficient self‐propulsion in acidic environments, and as a magnetic component enabling complete motion control. The new microrockets display longer lifetime and higher propulsion efficiency compared to previously reported active metal zinc‐based microrockets due to the chemical properties of iron and the unique structure of the microrockets. These iron‐based microrockets also demonstrate unique and attractive cargo towing and autonomous release capabilities. The latter is realized upon loss of the magnetic properties due to acid‐driven iron dissolution. More interestingly, these bubble‐propelled microrockets assemble via magnetic interactions into a variety of complex configurations and train structures, which enrich the behavior of micromachines. Modeling of the magnetic forces during the microrocket assembly and cargo capture confirms these unique experimentally observed assembly and cargo‐towing behaviors. These findings provide a new concept of blending propellant and magnetic components into one, toward simplifying the design and fabrication of artificial micro/nanomachines, realizing new functions and capabilities for a variety of future applications.     

Metamaterial-based graphene thermal emitter

A thermal emitter composed of a frequency-selective surface metamaterial layer and a hexagonal boron nitride-encapsulated graphene filament is demonstrated. The broadband thermal emission of the metamaterial (consisting of ring resonators) was tailored into two discrete bands, and the measured reflection and emission spectra agreed well with the simulation results. The high modulation frequencies that can be obtained in these devices, coupled with their operation in air, confirm their feasibility for use in applications such as gas sensing.

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Map‐aided localization in sparse global positioning system environments using vision and particle filtering

A map‐aided localization approach using vision, inertial sensors when available, and a particle filter is proposed and empirically evaluated. The approach, termed PosteriorPose, uses a Bayesian particle filter to augment global positioning system (GPS) and inertial navigation solutions with vision‐based measurements of nearby lanes and stop lines referenced against a known map of environmental features. These map‐relative measurements are shown to improve the quality of the navigation solution when GPS is available, and they are shown to keep the navigation solution converged in extended GPS blackouts. Measurements are incorporated with careful hypothesis testing and error modeling to account for non‐Gaussian and multimodal errors committed by GPS and vision‐based detection algorithms. Using a set of data collected with Cornell's autonomous car, including a measure of truth via a high‐precision differential corrections service, an experimental investigation of important design elements of the PosteriorPose estimator is conducted. The algorithm is shown to statistically outperform a tightly coupled GPS/inertial navigation solution both in full GPS coverage and in extended GPS blackouts. Statistical performance is also studied as a function of road type, filter likelihood models, bias models, and filter integrity tests. © 2011 Wiley Periodicals, Inc.     

Static timing analysis for modeling QoS in networks-on-chip

Networks-on-chip (NoCs) are used in a growing number of SoCs and multi-core processors. Because messages compete for the NoC’s shared resources, quality of service and resource allocation are major concerns for system designers. In particular, a model for the properties of packet delivery through the network is desirable. We present a methodology for packet-level static timing analysis in NoCs. Our methodology quickly and accurately gauges the performance parameters of a virtual-channel wormhole NoC without simulation. The network model can handle any topology, link capacities, and buffer sizes. It provides per-flow delay analysis that is orders-of-magnitude faster than simulation while being significantly more accurate than prior static modeling techniques. Using a carefully derived and reduced Markov chain, the model can statically represent the dynamic network state. Usage of the model in a placement optimization problem is shown as an example application.     

A typology of user liability to IT addiction

To date, information systems (IS) research mainly has provided a monolithic view of information technology (IT) use, considering it to be a desired behaviour with positive outcomes. However, given the dramatic increase in the use of technology during the last few years, susceptibility to IT addiction is increasingly becoming an important issue for technology users and IS researchers. In this paper, we report the results of a study that focuses on identifying variations in user liability to IT addiction, which reflects the susceptibility of individual users to develop IT addiction. First, a review of the literature in different disciplines (e.g. health, psychology and IS) allows us to better understand the concepts of IT addiction and liability to addiction. The literature review also provides an overview of the antecedents and consequences associated with IT addiction. Then, building on the analysis of 15 in‐depth interviews and 182 exploratory open‐ended surveys collected from smartphone users, we apply the concept of liability to addiction in the IT use context and propose a typological theory of user liability to IT addiction. Our typology reveals five ideal types; each can be associated to a user profile (addict, fanatic, highly engaged, regular and thoughtful ). Building upon both the extant literature and our results, we put forth propositions to extend the theoretical contributions of the study. We finally discuss the contributions and implications of our paper for research and practice.     

Safety implications of cultural and cognitive issues in nuclear power plant operation

This research project was designed to investigate cultural and cognitive issues related to the work of nuclear power plant operators during their time on the job in the control room and during simulator training (emergency situations), in order to show how these issues impact on plant safety. The modeling of the operators work deals with the use of operational procedures, the constant changes in the focus of attention and the dynamics of the conflicting activities. The paper focuses on the relationships between the courses of action of the different operators and the constraints imposed by their working environment. It shows that the safety implications of the control room operators' cognitive and cultural issues go far beyond the formal organizational constructs usually implied. Our findings indicate that the competence required for the operators are concerned with developing the possibility of constructing situation awareness, managing conflicts, gaps and time problems created by ongoing task procedures, and dealing with distractions, developing skills for collaborative work.     

Far-infrared absorption by phonons and librons in solid H2 and D2 in the ordered state

We present an experimental study of the infrared absorption spectra of solid, enriched ortho-hydrogen and para-deuterium in the ordered state for concentrations x of J = 1 molecules between 0.65 and 0.98 and temperatures from 0.9 to 11K. Comparison is made to theoretical expressions and numerical results for the absorption due to various microscopic processes, involving phonons and combinations oflibrons and phonons, which couple to the dipole moment induced by the electric quadrupole (EQ) fields of J = 1 molecules. The concentration dependence of the sharp, low-frequency optical phonon has also been studied. The integrated intensity of this feature is found to be quadratic in x and the frequency is well described by (x) = a + bx ²,which is the expected behavior for shifts arising from pairwise EQQ interactions. For constant x, the temperature dependence of the intensity of this phonon scales with the square of the long-range orientational order parameter. Our measurements of this quantity are compared to NMR determinations of the temperature dependence of the Pake splitting in the ordered state.Supported financially by the Stichting FOM.