Showing papers by "University of Central Florida published in 2013"

Hofstadter’s butterfly and the fractal quantum Hall effect in moiré superlattices

Abstract: Moire superlattices arising in bilayer graphene coupled to hexagonal boron nitride provide a periodic potential modulation on a length scale ideally suited to studying the fractal features of the Hofstadter energy spectrum in large magnetic fields. In 1976 Douglas Hofstadter predicted that electrons in a lattice subjected to electrostatic and magnetic fields would show a characteristic energy spectrum determined by the interplay between two quantizing fields. The expected spectrum would feature a repeating butterfly-shaped motif, known as Hofstadter's butterfly. The experimental realization of the phenomenon has proved difficult because of the problem of producing a sufficiently disorder-free superlattice where the length scales for magnetic and electric field can truly compete with each other. Now that goal has been achieved — twice. Two groups working independently produced superlattices by placing ultraclean graphene (Ponomarenko et al.) or bilayer graphene (Kim et al.) on a hexagonal boron nitride substrate and crystallographically aligning the films at a precise angle to produce moire pattern superstructures. Electronic transport measurements on the moire superlattices provide clear evidence for Hofstadter's spectrum. The demonstrated experimental access to a fractal spectrum offers opportunities for the study of complex chaotic effects in a tunable quantum system. Electrons moving through a spatially periodic lattice potential develop a quantized energy spectrum consisting of discrete Bloch bands. In two dimensions, electrons moving through a magnetic field also develop a quantized energy spectrum, consisting of highly degenerate Landau energy levels. When subject to both a magnetic field and a periodic electrostatic potential, two-dimensional systems of electrons exhibit a self-similar recursive energy spectrum1. Known as Hofstadter’s butterfly, this complex spectrum results from an interplay between the characteristic lengths associated with the two quantizing fields1,2,3,4,5,6,7,8,9,10, and is one of the first quantum fractals discovered in physics. In the decades since its prediction, experimental attempts to study this effect have been limited by difficulties in reconciling the two length scales. Typical atomic lattices (with periodicities of less than one nanometre) require unfeasibly large magnetic fields to reach the commensurability condition, and in artificially engineered structures (with periodicities greater than about 100 nanometres) the corresponding fields are too small to overcome disorder completely11,12,13,14,15,16,17. Here we demonstrate that moire superlattices arising in bilayer graphene coupled to hexagonal boron nitride provide a periodic modulation with ideal length scales of the order of ten nanometres, enabling unprecedented experimental access to the fractal spectrum. We confirm that quantum Hall features associated with the fractal gaps are described by two integer topological quantum numbers, and report evidence of their recursive structure. Observation of a Hofstadter spectrum in bilayer graphene means that it is possible to investigate emergent behaviour within a fractal energy landscape in a system with tunable internal degrees of freedom.

HON4D: Histogram of Oriented 4D Normals for Activity Recognition from Depth Sequences

Abstract: We present a new descriptor for activity recognition from videos acquired by a depth sensor. Previous descriptors mostly compute shape and motion features independently, thus, they often fail to capture the complex joint shape-motion cues at pixel-level. In contrast, we describe the depth sequence using a histogram capturing the distribution of the surface normal orientation in the 4D space of time, depth, and spatial coordinates. To build the histogram, we create 4D projectors, which quantize the 4D space and represent the possible directions for the 4D normal. We initialize the projectors using the vertices of a regular polychoron. Consequently, we refine the projectors using a discriminative density measure, such that additional projectors are induced in the directions where the 4D normals are more dense and discriminative. Through extensive experiments, we demonstrate that our descriptor better captures the joint shape-motion cues in the depth sequence, and thus outperforms the state-of-the-art on all relevant benchmarks.

Multi-source Multi-scale Counting in Extremely Dense Crowd Images

Abstract: We propose to leverage multiple sources of information to compute an estimate of the number of individuals present in an extremely dense crowd visible in a single image. Due to problems including perspective, occlusion, clutter, and few pixels per person, counting by human detection in such images is almost impossible. Instead, our approach relies on multiple sources such as low confidence head detections, repetition of texture elements (using SIFT), and frequency-domain analysis to estimate counts, along with confidence associated with observing individuals, in an image region. Secondly, we employ a global consistency constraint on counts using Markov Random Field. This caters for disparity in counts in local neighborhoods and across scales. We tested our approach on a new dataset of fifty crowd images containing 64K annotated humans, with the head counts ranging from 94 to 4543. This is in stark contrast to datasets used for existing methods which contain not more than tens of individuals. We experimentally demonstrate the efficacy and reliability of the proposed approach by quantifying the counting performance.

Mature HIV-1 capsid structure by cryo-electron microscopy and all-atom molecular dynamics

Abstract: Retroviral capsid proteins are conserved structurally but assemble into different morphologies. The mature human immunodeficiency virus-1 (HIV-1) capsid is best described by a 'fullerene cone' model, in which hexamers of the capsid protein are linked to form a hexagonal surface lattice that is closed by incorporating 12 capsid-protein pentamers. HIV-1 capsid protein contains an amino-terminal domain (NTD) comprising seven α-helices and a β-hairpin, a carboxy-terminal domain (CTD) comprising four α-helices, and a flexible linker with a 310-helix connecting the two structural domains. Structures of the capsid-protein assembly units have been determined by X-ray crystallography; however, structural information regarding the assembled capsid and the contacts between the assembly units is incomplete. Here we report the cryo-electron microscopy structure of a tubular HIV-1 capsid-protein assembly at 8 A resolution and the three-dimensional structure of a native HIV-1 core by cryo-electron tomography. The structure of the tubular assembly shows, at the three-fold interface, a three-helix bundle with critical hydrophobic interactions. Mutagenesis studies confirm that hydrophobic residues in the centre of the three-helix bundle are crucial for capsid assembly and stability, and for viral infectivity. The cryo-electron-microscopy structures enable modelling by large-scale molecular dynamics simulation, resulting in all-atom models for the hexamer-of-hexamer and pentamer-of-hexamer elements as well as for the entire capsid. Incorporation of pentamers results in closer trimer contacts and induces acute surface curvature. The complete atomic HIV-1 capsid model provides a platform for further studies of capsid function and for targeted pharmacological intervention.

Anderson localization of light

Abstract: The Anderson localization of light within disordered media has become a topic of great interest in recent years. Here the characterization of the effect and its related phenomena are reviewed, with a discussion on the role that nonlinearity and quantum correlated photons can play.

Iron-based bulk metallic glasses

Abstract: The current status of research and development in Fe-based bulk metallic glasses (BMGs) is reviewed. Bulk metallic glasses are relatively new materials possessing a glassy structure and large section thickness. These materials have an exciting combination of properties such as high mechanical strength, good thermal stability, large supercooled liquid region and potential for easy forming. Ever since the first synthesis of an Fe-based BMG in an Fe–Al–Ga–P–C–B system in 1995, there has been intense activity on the synthesis and characterisation of Fe-based BMGs. These BMGs exhibit some unique characteristics which have not been obtained in conventional Fe-based crystalline alloys. This uniqueness has led to practical uses of these bulk glassy alloys as soft magnetic and structural materials. This review presents the recent results on the glass-forming ability, structure, thermal stability, mechanical properties, corrosion behaviour, soft magnetic properties and applications of Fe-based bulk glassy a...

A Review of Power Decoupling Techniques for Microinverters With Three Different Decoupling Capacitor Locations in PV Systems

Abstract: The reliability of the microinverter is a very important feature that will determine the reliability of the ac-module photovoltaic (PV) system. Recently, many topologies and techniques have been proposed to improve its reliability. This paper presents a thorough study for different power decoupling techniques in single-phase microinverters for grid-tie PV applications. These power decoupling techniques are categorized into three groups in terms of the decoupling capacitor locations: 1) PV-side decoupling; 2) dc-link decoupling; and 3) ac-side decoupling. Various techniques and topologies are presented, compared, and scrutinized in scope of the size of decoupling capacitor, efficiency, and control complexity. Also, a systematic performance comparison is presented for potential power decoupling topologies and techniques.

Highly ordered MnO₂ nanopillars for enhanced supercapacitor performance

Abstract: This report demonstrates a simple, but efficient method to print highly ordered nanopillars without the use of sacrificial templates or any expensive equipment. The printed polymer structure is used as a scaffold to deposit electrode material (manganese dioxide) for making supercapacitors. The simplicity of the fabrication method together with superior power density and energy density make this supercapacitor electrode very attractive for the next-generation energy storage systems.

Blended Learning: A Dangerous Idea?.

Abstract: The authors make the case that implementation of a successful blended learning program requires alignment of institutional, faculty, and student goals. Reliable and robust infrastructure must be in place to support students and faculty. Continuous evaluation can effectively track the impact of blended learning on students, faculty, and the institution. These data are used to inform stakeholders and impact policy to improve faculty development and other support structures necessary for success. This iterative loop of continuous quality improvement is augmented by faculty scholarship of teaching and learning research. The evolution of blended learning at the University of Central Florida is used as a model and research collected over sixteen years illustrates that with proper support and planning, blended learning can result in positive institutional transformation.

Video Object Segmentation through Spatially Accurate and Temporally Dense Extraction of Primary Object Regions

Abstract: In this paper, we propose a novel approach to extract primary object segments in videos in the `object proposal' domain. The extracted primary object regions are then used to build object models for optimized video segmentation. The proposed approach has several contributions: First, a novel layered Directed Acyclic Graph (DAG) based framework is presented for detection and segmentation of the primary object in video. We exploit the fact that, in general, objects are spatially cohesive and characterized by locally smooth motion trajectories, to extract the primary object from the set of all available proposals based on motion, appearance and predicted-shape similarity across frames. Second, the DAG is initialized with an enhanced object proposal set where motion based proposal predictions (from adjacent frames) are used to expand the set of object proposals for a particular frame. Last, the paper presents a motion scoring function for selection of object proposals that emphasizes high optical flow gradients at proposal boundaries to discriminate between moving objects and the background. The proposed approach is evaluated using several challenging benchmark videos and it outperforms both unsupervised and supervised state-of-the-art methods.

Psychometric Evaluation of the Moral Injury Events Scale

Abstract: Literature describing the phenomenology of the stress of combat suggests that war-zone experiences may lead to adverse psychological outcomes such as post-traumatic stress disorder not only because they expose persons to life threat and loss but also because they may contradict deeply held moral and ethical beliefs and expectations. We sought to develop and validate a measure of potentially morally injurious events as a necessary step toward studying moral injury as a possible adverse consequence of combat. We administered an 11-item, self-report Moral Injury Events Scale to active duty Marines 1 week and 3 months following war-zone deployment. Two items were eliminated because of low item-total correlations. The remaining 9 items were subjected to an exploratory factor analysis, which revealed two latent factors that we labeled perceived transgressions and perceived betrayals; these were confirmed via confirmatory factor analysis on an independent sample. The overall Moral Injury Events Scale and...

Psychosocial Treatments for Schizophrenia

Abstract: The current state of the literature regarding psychosocial treatments for schizophrenia is reviewed within the frameworks of the recovery model of mental health and the expanded stress-vulnerability model. Interventions targeting specific domains of functioning, age groups, stages of illness, and human service system gaps are classified as evidence-based practices or promising practices according to the extent to which their efficacy is currently supported by meta-analyses and individual randomized controlled trials (RCTs). Evidence-based practices include assertive community treatment (ACT), cognitive behavior therapy (CBT) for psychosis, cognitive remediation, family psychoeducation, illness self-management training, social skills training, and supported employment. Promising practices include cognitive adaptive therapy, CBT for posttraumatic stress disorder, first-episode psychosis intervention, healthy lifestyle interventions, integrated treatment for co-occurring disorders, interventions targeting older individuals, peer support services, physical disease management, prodromal stage intervention, social cognition training, supported education, and supported housing. Implications and future directions are discussed.

Spatiotemporal Deformable Part Models for Action Detection

Abstract: Deformable part models have achieved impressive performance for object detection, even on difficult image datasets. This paper explores the generalization of deformable part models from 2D images to 3D spatiotemporal volumes to better study their effectiveness for action detection in video. Actions are treated as spatiotemporal patterns and a deformable part model is generated for each action from a collection of examples. For each action model, the most discriminative 3D sub volumes are automatically selected as parts and the spatiotemporal relations between their locations are learned. By focusing on the most distinctive parts of each action, our models adapt to intra-class variation and show robustness to clutter. Extensive experiments on several video datasets demonstrate the strength of spatiotemporal DPMs for classifying and localizing actions.

Linear-Quadratic Optimal Control Problems for Mean-Field Stochastic Differential Equations

Abstract: Linear-quadratic optimal control problems are considered for mean-field stochastic differential equations with deterministic coefficients. By a variational method, the optimality system is derived, which is a linear mean-field forward-backward stochastic differential equation. Using a decoupling technique, two Riccati differential equations are obtained which are uniquely solvable under certain conditions. Then a feedback representation is obtained for the optimal control.

Bio-distribution and in vivo antioxidant effects of cerium oxide nanoparticles in mice

Abstract: Cerium oxide nanoparticles have oxygen defects in their lattice structure that enables them to act as a regenerative free radical scavenger in a physiological environment. We performed a comprehensive in vivo analysis of the biological distribution and antioxidant capabilities of nanoceria administered to mice perorally (PO), intravenously (IV), or intraperitoneally (IP) by dosing animals weekly for 2 or 5 weeks with 0.5 mg kg(-1) nanoceria. Next, we examined if nanoceria administration would decrease ROS production in mice treated with carbon tetrachloride (CCl(4)). Our results showed that the most extensive and cumulative nano-deposition was via IV and IP administered while PO administration showed mice excreted greater than 95% of their nanoceria within 24 h. Organ deposition for IV and IP mice was greatest in the spleen followed by the liver, lungs, and kidneys. Elimination for all administration routes was through feces. Nanoceria administration showed no overt toxicity, however, WBC counts were elevated with IV and IP administration. Our in vivo studies show that nanoceria administration to mice with induced liver toxicity (by CCl(4)) showed similar findings to mice treated with N-acetyl cystine (NAC), a common therapeutic to reduce oxidative stress. Taken together, our studies show that nanoceria remains deposited in tissues and may decrease ROS, thereby suggesting that cerium oxide nanoparticles may be a useful antioxidant treatment for oxidative stress.

A Modified High-Efficiency LLC Converter With Two Transformers for Wide Input-Voltage Range Applications

Abstract: This paper proposed a modified LLC converter with two transformers in series, which has four operation configurations, covering the range of four times the minimum input voltage. To optimize the proposed LLC converter in an attempt to achieve good efficiency, a numerical method is developed based on the LLC converter's steady-state equations. In order to minimize the magnetizing current and thus minimize the conduction and core losses, an optimal objective is proposed to find the maximum magnetizing inductance. An optimization procedure and a design example are given. A 250-W 210-V output prototype with input voltage ranging from 25 to 100 V is built to verify the developed numerical model and optimal design method. The dc gain obtained from experimental data agrees pretty well with that from the developed numerical model. Two conventional LLC converters are designed using fundamental harmonic approximation and the proposed optimal design, respectively, to make comparison with the proposed LLC converter and validate the proposed optimal design. Experimental results show that the proposed converter with proposed optimal design can achieve the peak efficiency up to 98%, while maintaining a very wide input voltage range.

Forever young: SIRT3 a shield against mitochondrial meltdown, aging, and neurodegeneration.

Abstract: Caloric restriction, fasting, and exercise have long been recognized for their neuroprotective and lifespan-extending properties; however, the underlying mechanisms of these phenomena remain elusive. Such extraordinary benefits might be linked to the activation of sirtuins. In mammals, the sirtuin family has seven members (SIRT1-7), which diverge in tissue distribution, subcellular localization, enzymatic activity and targets. SIRT1, SIRT2, and SIRT3 have deacetylase activity. Their dependence on NAD+ directly links their activity to the metabolic status of the cell. High NAD+ levels convey neuroprotective effects, possibly via activation of sirtuin family members. Mitochondrial sirtuin 3 (SIRT3) has received much attention for its role in metabolism and aging. Specific small nucleotide polymorphisms (SNPs) in Sirt3 are linked to increased human lifespan. SIRT3 mediates the adaptation of increased energy demand during caloric restriction, fasting and exercise to increased production of energy equivalents. SIRT3 deacetylates and activates mitochondrial enzymes involved in fatty acid β-oxidation, amino acid metabolism, the electron transport chain, and antioxidant defenses. As a result, the mitochondrial energy metabolism increases. In addition, SIRT3 prevents apoptosis by lowering reactive oxygen species (ROS) and inhibiting components of the mitochondrial permeability transition pore. Mitochondrial deficits associated with aging and neurodegeneration might therefore be slowed or even prevented by SIRT3 activation. In addition, upregulating SIRT3 activity by dietary supplementation of sirtuin activating compounds might promote the beneficial effects of this enzyme. The goal of this review is to summarize emerging data supporting a neuroprotective action of SIRT3 against Alzheimer’s disease (AD), Huntington’s disease (HD), Parkinson’s disease (PD) and amyotrophic lateral sclerosis (ALS).

Exploring the Trade-off Between Accuracy and Observational Latency in Action Recognition

Abstract: An important aspect in designing interactive, action-based interfaces is reliably recognizing actions with minimal latency. High latency causes the system's feedback to lag behind user actions and thus significantly degrades the interactivity of the user experience. This paper presents algorithms for reducing latency when recognizing actions. We use a latency-aware learning formulation to train a logistic regression-based classifier that automatically determines distinctive canonical poses from data and uses these to robustly recognize actions in the presence of ambiguous poses. We introduce a novel (publicly released) dataset for the purpose of our experiments. Comparisons of our method against both a Bag of Words and a Conditional Random Field (CRF) classifier show improved recognition performance for both pre-segmented and online classification tasks. Additionally, we employ GentleBoost to reduce our feature set and further improve our results. We then present experiments that explore the accuracy/latency trade-off over a varying number of actions. Finally, we evaluate our algorithm on two existing datasets.

Cloud Computing: Theory and Practice

Abstract: Cloud Computing: Theory and Practice provides students and IT professionals with an in-depth analysis of the cloud from the ground up. Beginning with a discussion of parallel computing and architectures and distributed systems, the book turns to contemporary cloud infrastructures, how they are being deployed at leading companies such as Amazon, Google and Apple, and how they can be applied in fields such as healthcare, banking and science. The volume also examines how to successfully deploy a cloud application across the enterprise using virtualization, resource management and the right amount of networking support, including content delivery networks and storage area networks. Developers will find a complete introduction to application development provided on a variety of platforms. Learn about recent trends in cloud computing in critical areas such as: resource management, security, energy consumption, ethics, and complex systems Get a detailed hands-on set of practical recipes that help simplify the deployment of a cloud based system for practical use of computing clouds along with an in-depth discussion of several projects Understand the evolution of cloud computing and why the cloud computing paradigm has a better chance to succeed than previous efforts in large-scale distributed computing

Observation of asymmetric transport in structures with active nonlinearities.

Abstract: A mechanism for asymmetric transport which is based on parity-time-symmetric nonlinearities is presented. We show that in contrast to the case of conservative nonlinearities, an increase of the complementary conductance strength leads to a simultaneous increase of asymmetry and transmittance intensity. We experimentally demonstrate the phenomenon using a pair of coupled Van der Pol oscillators as a reference system, each with complementary anharmonic gain and loss conductances, connected to transmission lines. An equivalent optical setup is also proposed.

Customer Loyalty to the Salesperson and the Store: Examining Relationship Customers in an Upscale Retail Context

Abstract: Only recently has research interest in relationship marketing and customer loyalty converged in the retail context. Although this research shows that relationship customers maintain their primary loyalty to the salesperson, which then “spills over” and affects loyalty to the store, other research suggests that salesperson loyalty has direct effects on store-level outcomes, such as spending and word of mouth. However, this has not been comprehensively investigated, and relationship researchers have specifically called for research examining the effects of salesperson and store loyalty on store-level outcomes. Our research addresses this call, and shows that in an upscale retail context a relationship customer's loyalty to the salesperson is significantly related to store loyalty as well as the important store-level outcomes of share of purchases, word of mouth and competitive resistance.

Nanoceria: A Rare-Earth Nanoparticle as a Novel Anti-Angiogenic Therapeutic Agent in Ovarian Cancer

Abstract: Ovarian cancer (OvCa) is the fifth most common cause of death from all cancers among women in United Sates and the leading cause of death from gynecological malignancies. While most OvCa patients initially respond to surgical debulking and chemotherapy, 75% of patients later succumb to the disease. Thus, there is an urgent need to test novel therapeutic agents to counteract the high mortality rate associated with OvCa. In this context, we have developed and engineered Nanoceria (NCe), nanoparticles of cerium oxide, possessing anti-oxidant properties, to be used as a therapeutic agent in OvCa. We show for the first time that NCe significantly inhibited production of reactive oxygen species (ROS) in A2780 cells, attenuated growth factor (SDF1, HB-EGF, VEGF165 and HGF) mediated cell migration and invasion of SKOV3 cells, without affecting the cell proliferation. NCe treatment also inhibited VEGF165 induced proliferation, capillary tube formation, activation of VEGFR2 and MMP2 in human umbilical vascular endothelial cells (HUVEC). NCe (0.1 mg/kg body weigh) treatment of A2780 ovarian cancer cells injected intra-peritoneally in nude mice showed significant reduction (p<0.002) in tumor growth accompanied by decreased tumor cell proliferation as evident from reduced tumor size and Ki67 staining. Accumulation of NCe was found in tumors isolated from treated group using transmission electron microscopy (TEM) and inductively coupled plasma mass spectroscopy (ICP-MS). Reduction of the tumor mass was accompanied by attenuation of angiogenesis, as observed by reduced CD31 staining and specific apoptosis of vascular endothelial cells. Collectively, these results indicate that cerium oxide based NCe is a novel nanoparticle that can potentially be used as an anti-angiogenic therapeutic agent in ovarian cancer.