Showing papers by "University of Central Florida published in 2010"

Observation of parity–time symmetry in optics

Abstract: One of the fundamental axioms of quantum mechanics is associated with the Hermiticity of physical observables 1 . In the case of the Hamiltonian operator, this requirement not only implies real eigenenergies but also guarantees probability conservation. Interestingly, a wide class of non-Hermitian Hamiltonians can still show entirely real spectra. Among these are Hamiltonians respecting parity‐time (PT) symmetry 2‐7 . Even though the Hermiticity of quantum observables was never in doubt, such concepts have motivated discussions on several fronts in physics, including quantum field theories 8 , nonHermitian Anderson models 9 and open quantum systems 10,11 , to mention a few. Although the impact of PT symmetry in these fields is still debated, it has been recently realized that optics can provide a fertile ground where PT-related notions can be implemented and experimentally investigated 12‐15 . In this letter we report the first observation of the behaviour of a PT optical coupled system that judiciously involves a complex index potential. We observe both spontaneous PT symmetry breaking and power oscillations violating left‐right symmetry. Our results may pave the way towards a new class of PT-synthetic materials with intriguing and unexpected properties that rely on non-reciprocal light propagation and tailored transverse energy flow. Before we introduce the concept of spacetime reflection in optics, we first briefly outline some of the basic aspects of this symmetry within the context of quantum mechanics. In general, a Hamiltonian HD p 2 =2mCV(x

Oxidase activity of polymeric coated cerium oxide nanoparticles

Abstract: Methods, systems, compositions include biocompatible polymer coated nanoceria that function as aqueous redox catalyst with enhanced activity at an acidic to moderately alkaline pH value between 1 and 8. The compositions are used as oxidizing agents for decomposition, decontamination or inactivation of organic contaminants, such as, pesticides and chemical warfare agents. Another use includes nanoceria as targetable nanocatalyst prepared by conjugating various targeting ligands to the nanoparticle coating to form a colorimetric or fluorescent probe in immunoassays and other molecule binding assays that involve the use of a molecule in solution that changes the color of the solution or emits a fluorescent signal, where localization of nanoceria to organs or tissue is assessed by treatment with an oxidation sensitive dye or other detection devices. Versatility and uses of the nanoceria compositions are controlled by pH value, choice of dye substrate and thickness of the polymer coating on the ceria nanoparticles.

The cognitive underpinnings of effective teamwork: a meta-analysis.

Abstract: Major theories of team effectiveness position emergent collective cognitive processes as central drivers of team performance. We meta-analytically cumulated 231 correlations culled from 65 independent studies of team cognition and its relations to teamwork processes, motivational states, and performance outcomes. We examined both broad relationships among cognition, behavior, motivation, and performance, as well as 3 underpinnings of team cognition as potential moderators of these relationships. Findings reveal there is indeed a cognitive foundation to teamwork; team cognition has strong positive relationships to team behavioral process, motivational states, and team performance. Meta-analytic regressions further indicate that team cognition explains significant incremental variance in team performance after the effects of behavioral and motivational dynamics have been controlled. The nature of emergence, form of cognition, and content of cognition moderate relationships among cognition, process, and performance, as do task interdependence and team type. Taken together, these findings not only cumulate extant research on team cognition but also provide a new interpretation of the impact of underlying dimensions of cognition as a way to frame and extend future research.

Unidirectional nonlinear PT -symmetric optical structures

Abstract: We show that nonlinear optical structures involving a balanced gain-loss profile can act as unidirectional optical valves. This is made possible by exploiting the interplay between the fundamental symmetries of parity ($\mathcal{P}$) and time ($\mathcal{T}$), with optical nonlinear effects. This unidirectional dynamics is specifically demonstrated for the case of an integrable $\mathcal{PT}$-symmetric nonlinear system.

The language of US corporate environmental disclosure

Abstract: We rely on prior work in environmental disclosure and corporate impression management to investigate whether there are self-serving biases present in the language and verbal tone used in corporations’ environmental disclosures. Specifically, we argue that the degree of bias in these narratives varies systematically based on firm environmental performance, hypothesizing that disclosures of worse environmental performers exhibit significantly more “optimism” and less “certainty” than their better-performing counterparts. We test our two hypotheses using a cross-sectional sample of corporate environmental disclosures contained in US 10-K annual reports. Utilizing the content analysis software DICTION to determine “optimism” and “certainty” scores for the disclosures, we find empirical support for both hypotheses. Our study contributes significantly to research in environmental disclosure by investigating bias in the use of language and verbal tone as a tool for managing stakeholder impressions and by finding empirical support for this role. Thus, the language and verbal tone used in corporate environmental disclosures, in addition to their amount and thematic content, should be considered when investigating the relation between corporate disclosure and performance.

VizWiz: nearly real-time answers to visual questions

Abstract: Visual information pervades our environment. Vision is used to decide everything from what we want to eat at a restaurant and which bus route to take to whether our clothes match and how long until the milk expires. Individually, the inability to interpret such visual information is a nuisance for blind people who often have effective, if inefficient, work-arounds to overcome them. Collectively, however, they can make blind people less independent. Specialized technology addresses some problems in this space, but automatic approaches cannot yet answer the vast majority of visual questions that blind people may have. VizWiz addresses this shortcoming by using the Internet connections and cameras on existing smartphones to connect blind people and their questions to remote paid workers' answers. VizWiz is designed to have low latency and low cost, making it both competitive with expensive automatic solutions and much more versatile.

VizWiz: nearly real-time answers to visual questions

Abstract: The lack of access to visual information like text labels, icons, and colors can cause frustration and decrease independence for blind people. Current access technology uses automatic approaches to address some problems in this space, but the technology is error-prone, limited in scope, and quite expensive. In this paper, we introduce VizWiz, a talking application for mobile phones that offers a new alternative to answering visual questions in nearly real-time - asking multiple people on the web. To support answering questions quickly, we introduce a general approach for intelligently recruiting human workers in advance called quikTurkit so that workers are available when new questions arrive. A field deployment with 11 blind participants illustrates that blind people can effectively use VizWiz to cheaply answer questions in their everyday lives, highlighting issues that automatic approaches will need to address to be useful. Finally, we illustrate the potential of using VizWiz as part of the participatory design of advanced tools by using it to build and evaluate VizWiz::LocateIt, an interactive mobile tool that helps blind people solve general visual search problems.

Airy–Bessel wave packets as versatile linear light bullets

Abstract: The generation of spatiotemporal optical wave packets that are resistant to both dispersion and diffraction are attractive for bioimaging applications and plasma physics. By combining Bessel beams in the transverse plane with temporal Airy pulses, scientists now report the first observation of a class of versatile three-dimensional linear light ‘bullets’.

Chaotic invariants of Lagrangian particle trajectories for anomaly detection in crowded scenes

Abstract: A novel method for crowd flow modeling and anomaly detection is proposed for both coherent and incoherent scenes. The novelty is revealed in three aspects. First, it is a unique utilization of particle trajectories for modeling crowded scenes, in which we propose new and efficient representative trajectories for modeling arbitrarily complicated crowd flows. Second, chaotic dynamics are introduced into the crowd context to characterize complicated crowd motions by regulating a set of chaotic invariant features, which are reliably computed and used for detecting anomalies. Third, a probabilistic framework for anomaly detection and localization is formulated. The overall work-flow begins with particle advection based on optical flow. Then particle trajectories are clustered to obtain representative trajectories for a crowd flow. Next, the chaotic dynamics of all representative trajectories are extracted and quantified using chaotic invariants known as maximal Lyapunov exponent and correlation dimension. Probabilistic model is learned from these chaotic feature set, and finally, a maximum likelihood estimation criterion is adopted to identify a query video of a scene as normal or abnormal. Furthermore, an effective anomaly localization algorithm is designed to locate the position and size of an anomaly. Experiments are conducted on known crowd data set, and results show that our method achieves higher accuracy in anomaly detection and can effectively localize anomalies.

The effects of modern mathematics computer games on mathematics achievement and class motivation

Abstract: This study examined the effects of a computer game on students' mathematics achievement and motivation, and the role of prior mathematics knowledge, computer skill, and English language skill on their achievement and motivation as they played the game. A total of 193 students and 10 teachers participated in this study. The teachers were randomly assigned to experimental and control groups. A mixed method of quantitative and interviews were used with Multivariate Analysis of Co-Variance to analyze the data. The results indicated significant improvement of the achievement of the experimental versus control group. No significant improvement was found in the motivation of the groups. Students who played the games in their classrooms and school labs reported greater motivation compared to the ones who played the games only in the school labs. Prior knowledge, computer and English language skill did not play significant roles in achievement and motivation of the experimental group.

Bulk Metallic Glasses

Abstract: Introduction Motivation Advanced Materials Rapid Solidification Processing Mechanical Alloying Outline of the Book Metallic Glasses Distinction between Crystals and Glasses Differences between Amorphous Alloys and Metallic Glasses The Concepts of Glass Formation Thermodynamics and Kinetics of Glass Formation Methods to Synthesize Metallic Glasses Bulk Metallic Glasses Potential Resources of Literature on Metallic Glasses Glass-Forming Ability of Alloys Critical Cooling Rate Reduced Glass Transition Temperature Deep Eutectics Topological Models Bulk Metallic Glasses Inoue Criteria Exceptions to the Above Criteria New Criteria Transformation Temperatures of Glasses Thermodynamic Modeling Structural and Topological Parameters Physical Properties Computational Approaches Miscellaneous Criteria Criteria for Glass Formation by Non-Solidification Methods Synthesis of Bulk Metallic Glasses Principles of Rapid Solidification Processing General Techniques to Achieve High Rates of Solidification Melt Spinning Bulk Metallic Glasses Bulk Metallic Glass Casting Methods Bulk Metallic Glass Composites Mechanical Alloying Bulk Metallic Glass Foams Crystallization Behavior Methodology Crystallization Modes in Melt-Spun Ribbons Differences in the Crystallization Behavior between Melt-Spun Ribbons and Bulk Metallic Glasses Thermal Stability of Metallic Glasses Crystallization Temperatures and Their Compositional Dependence Annealing of Bulk Metallic Glasses Effect of Environment Effect of Pressure during Annealing Physical Properties Density Thermal Expansion Diffusion Electrical Resistivity Specific Heat Viscosity Corrosion Behavior Terminology and Methodology Copper-Based Bulk Metallic Glasses Iron-Based Bulk Metallic Glasses Magnesium-Based Bulk Glassy Alloys Nickel-Based Bulk Metallic Glasses Titanium-Based Bulk Metallic Glasses Zirconium-Based Bulk Metallic Glasses Other Bulk Metallic Glassy Alloys Mechanical Behavior Deformation Behavior Deformation Maps Temperature Rise at Shear Bands Strength Ductility Fatigue Yield Behavior BMG Composites Magnetic Properties Soft Magnetic Materials Nanocrystalline Alloys Hard Magnetic Materials Applications Special Characteristics of Bulk Metallic Glasses Structural Applications Chemical Applications Magnetic Applications Miscellaneous Applications Epilogue Size and Shape Mechanical Properties Magnetic Properties Fundamental Properties Index References appear at the end of each chapter.

Human Action Recognition in Videos Using Kinematic Features and Multiple Instance Learning

Abstract: We propose a set of kinematic features that are derived from the optical flow for human action recognition in videos. The set of kinematic features includes divergence, vorticity, symmetric and antisymmetric flow fields, second and third principal invariants of flow gradient and rate of strain tensor, and third principal invariant of rate of rotation tensor. Each kinematic feature, when computed from the optical flow of a sequence of images, gives rise to a spatiotemporal pattern. It is then assumed that the representative dynamics of the optical flow are captured by these spatiotemporal patterns in the form of dominant kinematic trends or kinematic modes. These kinematic modes are computed by performing principal component analysis (PCA) on the spatiotemporal volumes of the kinematic features. For classification, we propose the use of multiple instance learning (MIL) in which each action video is represented by a bag of kinematic modes. Each video is then embedded into a kinematic-mode-based feature space and the coordinates of the video in that space are used for classification using the nearest neighbor algorithm. The qualitative and quantitative results are reported on the benchmark data sets.

Ultralight multiwalled carbon nanotube aerogel.

Abstract: Ultralight multiwalled carbon nanotube (MWCNT) aerogel is fabricated from a wet gel of well-dispersed pristine MWCNTs. On the basis of a theoretical prediction that increasing interaction potential between CNTs lowers their critical concentration to form an infinite percolation network, poly(3-(trimethoxysilyl) propyl methacrylate) (PTMSPMA) is used to disperse and functionalize MWCNTs where the subsequent hydrolysis and condensation of PTMSPMA introduces strong and permanent chemical bonding between MWCNTs. The interaction is both experimentally and theoretically proven to facilitate the formation of a MWCNT percolation network, which leads to the gelation of MWCNT dispersion at ultralow MWCNT concentration. After removing the liquid component from the MWCNT wet gel, the lightest ever free-standing MWCNT aerogel monolith with a density of 4 mg/cm(3) is obtained. The MWCNT aerogel has an ordered macroporous honeycomb structure with straight and parallel voids in 50-150 μm separated by less than 100 nm thick walls. The entangled MWCNTs generate mesoporous structures on the honeycomb walls, creating aerogels with a surface area of 580 m(2)/g which is much higher than that of pristine MWCNTs (241 m(2)/g). Despite the ultralow density, the MWCNT aerogels have an excellent compression recoverable property as demonstrated by the compression test. The aerogels have an electrical conductivity of 3.2 × 10(-2) S·cm(-1) that can be further increased to 0.67 S·cm(-1) by a high-current pulse method without degrading their structures. The excellent compression recoverable property, hierarchically porous structure with large surface area, and high conductivity grant the MWCNT aerogels exceptional pressure and chemical vapor sensing capabilities.

Redox-active radical scavenging nanomaterials

Abstract: Reactive oxygen and nitrogen species play a critical role in many degenerative diseases and in aging. Nanomaterials, especially modified fullerenes and cerium oxide nanoparticles, have been shown to effectively protect mammalian cells against damage caused by increased reactive oxygen or nitrogen species, likely through their direct reaction with superoxide radical, since each of these materials has been shown to act as effective superoxide dismutase mimetics in vitro. This critical review discusses the chemistry of these nanomaterials and the context in which their radical scavenging activities have been studied in biological model systems. Current studies are focused on determining the uptake, metabolism, distribution, toxicity and fate of these nanomaterials in cell and animal model systems. Ultimately if shown to be safe, these nanomaterials have the potential to be used to reduce the damaging effects of radicals in biological systems (101 references).

Abruptly autofocusing waves.

Abstract: We introduce a new class of (2+1)D spatial and (3+1)D spatiotemporal waves that tend to autofocus in an abrupt fashion. While the maximum intensity of such a radial wave remains almost constant during propagation, it suddenly increases by orders of magnitude right before its focal point. These waves can be generated through the use of radially symmetric Airy waves or by appropriately superimposing Airy wave packets. Possible applications of such abruptly focusing beams are also discussed.

Social anxiety disorder: questions and answers for the DSM-V

Abstract: Background: This review evaluates the DSM-IV criteria of social anxiety disorder (SAD), with a focus on the generalized specifier and alternative specifiers, the considerable overlap between the DSM-IV diagnostic criteria for SAD and avoidant personality disorder, and developmental issues. Method: A literature review was conducted, using the validators provided by the DSM-V Spectrum Study Group. This review presents a number of options and preliminary recommendations to be considered for DSM-V. Results/Conclusions: Little supporting evidence was found for the current specifier, generalized SAD. Rather, the symptoms of individuals with SAD appear to fall along a continuum of severity based on the number of fears. Available evidence suggested the utility of a specifier indicating a ‘‘predominantly performance’’ variety of SAD. A specifier based on ‘‘fear of showing anxiety symptoms’’ (e.g., blushing) was considered. However, a tendency to show anxiety symptoms is a core fear in SAD, similar to acting or appearing in a certain way. More research is needed before considering subtyping SAD based on core fears. SAD was found to be a valid diagnosis in children and adolescents. Selective mutism could be considered in part as a young child’s avoidance response to social fears. Pervasive test anxiety may belong not only to SAD, but also to generalized anxiety disorder. The data are equivocal regarding whether to consider avoidant personality disorder simply a severe form of SAD. Secondary data analyses, field trials, and validity tests are needed to investigate the recommendations and options. Depression and Anxiety 27:168–189, 2010. r 2010 Wiley-Liss, Inc.

Selective hydrogen gas nanosensor using individual ZnO nanowire with fast response at room temperature

Abstract: In this work, we report on a single ZnO nanowire-based nanoscale sensor fabricated using focused ion beam (FIB/SEM) instrument. We studied the diameter dependence of the gas response and selectivity of ZnO nanowires (NWs) synthesized by chemical vapor phase growth method. The photoluminescence (PL) measurements were used to determine the deep levels related to defects which are presented in the ZnO nanomaterial as well as to evaluate the effect of thermal treatment in H2 atmosphere on the emission from ZnO nanowires. We show that sample annealed in hydrogen leads to passivation of recombination centers thus modifying the NWs properties. We studied the gas response and selectivity of these ZnO nanowires to H2 ,N H 3, i-Butane, CH4 gases at room temperature. Our results indicated that zinc oxide NWs hold a high promise for nanoscale sensor applications due to its capability to operate at room-temperature and its ability to tune the gas response and selectivity by the defect concentration and the diameter of ZnO nanowire. A method is proposed to reduce the nanosensor’s recovery time through the irradiation with an ultraviolet radiation pulse. The sensing mechanisms of ZnO nanowires will be discussed.

Accurate image localization based on google maps street view

Abstract: Finding an image's exact GPS location is a challenging computer vision problem that has many real-world applications. In this paper, we address the problem of finding the GPS location of images with an accuracy which is comparable to hand-held GPS devices. We leverage a structured data set of about 100,000 images build from Google Maps Street View as the reference images. We propose a localization method in which the SIFT descriptors of the detected SIFT interest points in the reference images are indexed using a tree. In order to localize a query image, the tree is queried using the detected SIFT descriptors in the query image. A novel GPS-tag-based pruning method removes the less reliable descriptors. Then, a smoothing step with an associated voting scheme is utilized; this allows each query descriptor to vote for the location its nearest neighbor belongs to, in order to accurately localize the query image. A parameter called Confidence of Localization which is based on the Kurtosis of the distribution of votes is defined to determine how reliable the localization of a particular image is. In addition, we propose a novel approach to localize groups of images accurately in a hierarchical manner. First, each image is localized individually; then, the rest of the images in the group are matched against images in the neighboring area of the found first match. The final location is determined based on the Confidence of Localization parameter. The proposed image group localization method can deal with very unclear queries which are not capable of being geolocated individually.

Historical Accumulation of Nonindigenous Forest Pests in the Continental United States

Abstract: Nonindigenous forest insects and pathogens affect a range of ecosystems, industries, and property owners in the United States. Evaluating temporal patterns in the accumulation of these nonindigenous forest pests can inform regulatory and policy decisions. We compiled a comprehensive species list to assess the accumulation rates of nonindigenous forest insects and pathogens established in the United States. More than 450 nonindigenous insects and at least 16 pathogens have colonized forest and urban trees since European settlement. Approximately 2.5 established nonindigenous forest insects per year were detected in the United States between 1860 and 2006. At least 14% of these insects and all 16 pathogens have caused notable damage to trees. Although sap feeders and foliage feeders dominated the comprehensive list, phloem- and wood-boring insects and foliage feeders were often more damaging than expected. Detections of insects that feed on phloem or wood have increased markedly in recent years.

Shape-dependent catalytic properties of Pt nanoparticles.

Abstract: Tailoring the chemical reactivity of nanomaterials at the atomic level is one of the most important challenges in catalysis research. In order to achieve this elusive goal, fundamental understanding of the geometric and electronic structure of these complex systems at the atomic level must be obtained. This article reports the influence of the nanoparticle shape on the reactivity of Pt nanocatalysts supported on γ-Al(2)O(3). Nanoparticles with analogous average size distributions (∼0.8-1 nm), but with different shapes, synthesized by inverse micelle encapsulation, were found to display distinct reactivities for the oxidation of 2-propanol. A correlation between the number of undercoordinated atoms at the nanoparticle surface and the onset temperature for 2-propanol oxidation was observed, demonstrating that catalytic properties can be controlled through shape-selective synthesis.

Modeling and Control of Three-Port DC/DC Converter Interface for Satellite Applications

Abstract: This paper presents the control strategy and power management for an integrated three-port converter, which interfaces one solar input port, one bidirectional battery port, and an isolated output port. Multimode operations and multiloop designs are vital for such multiport converters. However, control design is difficult for a multiport converter to achieve multifunctional power management because of various cross-coupled control loops. Since there are various modes of operation, it is challenging to define different modes and to further implement autonomous mode transition based on the energy state of the three power ports. A competitive method is used to realize smooth and seamless mode transition. Multiport converter has plenty of interacting control loops due to integrated power trains. It is difficult to design close-loop controls without proper decoupling method. A detailed approach is provided utilizing state-space averaging method to obtain the converter model under different modes of operation, and then a decoupling network is introduced to allow separate controller designs. Simulation and experimental results verify the converter control design and power management during various operational modes.