Showing papers by "Virginia Tech published in 2009"

An experimentally validated bimorph cantilever model for piezoelectric energy harvesting from base excitations

Abstract: Piezoelectric transduction has received great attention for vibration-to-electric energy conversion over the last five years. A typical piezoelectric energy harvester is a unimorph or a bimorph cantilever located on a vibrating host structure, to generate electrical energy from base excitations. Several authors have investigated modeling of cantilevered piezoelectric energy harvesters under base excitation. The existing mathematical modeling approaches range from elementary single-degree-of-freedom models to approximate distributed parameter solutions in the sense of Rayleigh–Ritz discretization as well as analytical solution attempts with certain simplifications. Recently, the authors have presented the closed-form analytical solution for a unimorph cantilever under base excitation based on the Euler–Bernoulli beam assumptions. In this paper, the analytical solution is applied to bimorph cantilever configurations with series and parallel connections of piezoceramic layers. The base excitation is assumed to be translation in the transverse direction with a superimposed small rotation. The closed-form steady state response expressions are obtained for harmonic excitations at arbitrary frequencies, which are then reduced to simple but accurate single-mode expressions for modal excitations. The electromechanical frequency response functions (FRFs) that relate the voltage output and vibration response to translational and rotational base accelerations are identified from the multi-mode and single-mode solutions. Experimental validation of the single-mode coupled voltage output and vibration response expressions is presented for a bimorph cantilever with a tip mass. It is observed that the closed-form single-mode FRFs obtained from the analytical solution can successfully predict the coupled system dynamics for a wide range of electrical load resistance. The performance of the bimorph device is analyzed extensively for the short circuit and open circuit resonance frequency excitations and the accuracy of the model is shown in all cases.

Longitudinal pathways linking child maltreatment, emotion regulation, peer relations, and psychopathology

Abstract: Background: The aim of this study was to investigate longitudinal relations among child maltreatment, emotion regulation, peer acceptance and rejection, and psychopathology. Methods: Data were collected on 215 maltreated and 206 nonmaltreated children (ages 6–12 years) from low‐income families. Children were evaluated by camp counselors on emotion regulation and internalizing and externalizing symptomatology and were nominated by peers for peer acceptance and rejection. Results: Structural equation modeling analyses revealed that experiencing neglect, physical and/or sexual abuse, multiple maltreatment subtypes, and earlier onset of maltreatment were related to emotion dysregulation. Lower emotion regulation (Time 1) was associated with higher externalizing symptomatology (Time 1) that contributed to later peer rejection (Time 2), which in turn was related to higher externalizing symptomatology (Time 2). Conversely, higher emotion regulation was predictive of higher peer acceptance over time, which was related to lower internalizing symptomatology controlling for initial levels of symptomatology. Conclusions: The findings emphasize the important role of emotion regulation as a risk or a protective mechanism in the link between earlier child maltreatment and later psychopathology through its influences on peer relations.

Permanent Magnet Synchronous and Brushless DC Motor Drives

Abstract: PART I: Introduction to Permanent Magnets and Machines and Converters and Control Chapter 1 Permanent Magnets and Machines Permanent Magnets Arrangement of PMs Magnetization of PMs PM ac Machines Fundamentals of Synchronous Machines Fundamental Synchronous Machine Relationships Core Losses Resistive Losses Initial Machine Design Cogging Torque Basic Types of PMSMs Based on Flux Paths Vibration and Noise Chapter 2 Introduction to Inverters and Their Control Power Device DC Input Source DC to ac Power Conversion Real Power Reactive Power Need for Inverter Control Pulse Width Modulation Hysteresis Current Control Space Vector Modulation Inverter Switching Delay Input Power Factor Correction Circuit Four-Quadrant Operation Converter Requirements PART II: Permanent Magnet Synchronous Machines and Their Control Chapter 3 Dynamic Modeling of Permanent Magnet Synchronous Machines Real-Time Model of a Two-Phase PMSM Transformation to Rotor Reference Frames Three-Phase to Two-Phase Transformation Zero Sequence Inductance Derivation Power Equivalence Electromagnetic Torque Steady-State Torque Characteristics Models in Flux Linkages Equivalent Circuits Per Unit Model Dynamic Simulation Small-Signal Equations of the PMSM Evaluation of Control Characteristics of the PMSM Computation of Time Responses Space Phasor Model Chapter 4 Control Strategies for a Permanent Magnet Synchronous Machine Vector Control Derivation of Vector Control Drive System Schematic Control Strategies Chapter 5 Flux-Weakening Operation Maximum Speed Flux-Weakening Algorithm Direct Flux Weakening Parameter Sensitivity Model-Free (Parameter-Insensitive) Flux-Weakening Method Six-Step Voltage and Constant Back EMF Control Strategies for PMSM Direct Steady-State Evaluation Flux Weakening in SMPM and IPM Synchronous Machines Chapter 6 Design of Current and Speed Controllers Current Controller Speed Controller Chapter 7 Parameter Sensitivity and Compensation Introduction Parameter Compensation through Air Gap Power Feedback Control Parameter Compensation by Reactive Power Feedback Control Chapter 8 Rotor Position Estimation and Position Sensorless Control Current Model Adaptive Scheme Sensing by External Signal Injection Current Model-Based Injection Scheme Position Estimation Using PWM Carrier Components PART III: Permanent Magnet Brushless DC Machines and Their Control Chapter 9 PM Brushless DC Machine Modeling of PM Brushless DC Motor Normalized System Equations The PMBDCM Drive Scheme Dynamic Simulation Chapter 10 Commutation Torque Ripple and Phase Advancing Commutation Torque Ripple Phase Advancing Dynamic Modeling Chapter 11 Half-Wave PMBDCM Drives Split Supply Converter Topology C-Dump Topology Variable DC Link Converter Topology Variable Voltage Converter Topology with Buck-Boost Front-End Chapter 12 Design of Current and Speed Controllers Transfer Function of Machine and Load Inverter Transfer Function Transfer Functions of Current and Speed Controllers Current Feedback Speed Feedback Design of Controllers Chapter 13 Sensorless Control of PMBDCM Drive Current Sensing Position Estimation Chapter 14 Special Issues Torque Smoothing Parameter Sensitivity of the PMBDCM Drive Faults and Their Diagnosis Vibration and Noise

Intercomparison, interpretation, and assessment of spring phenology in North America estimated from remote sensing for 1982-2006

Abstract: Shifts in the timing of spring phenology are a central feature of global change research. Long-term observations of plant phenology have been used to track vegetation responses to climate variability but are often limited to particular species and locations and may not represent synoptic patterns. Satellite remote sensing is instead used for continental to global monitoring. Although numerous methods exist to extract phenological timing, in particular start-of-spring (SOS), from time series of reflectance data, a comprehensive intercomparison and interpretation of SOS methods has not been conducted. Here, we assess 10 SOS methods for North America between 1982 and 2006. The techniques include consistent inputs from the 8 km Global Inventory Modeling and Mapping Studies Advanced Very High Resolution Radiometer NDVIg dataset, independent data for snow cover, soil thaw, lake ice dynamics, spring streamflow timing, over 16 000 individual measurements of ground-based phenology, and two temperature-driven models of spring phenology. Compared with an ensemble of the 10 SOS methods, we found that individual methods differed in average day-of-year estimates by � 60 days and in standard deviation by � 20 days. The ability of the satellite methods to retrieve SOS estimates was highest in northern latitudes and lowest in arid, tropical, and Mediterranean ecoregions. The ordinal rank of SOS methods varied geographically, as did the relationships between SOS estimates and the cryospheric/hydrologic metrics. Compared with ground observations, SOS estimates were more related to the first leaf and first flowers expanding phenological stages. We found no evidence for time trends in spring arrival from ground- or model-based data; using an ensemble estimate from two methods that were more closely related to ground observations than other methods, SOS

Spectrum Sensing for Cognitive Radio

Abstract: Spectrum sensing is the very task upon which the entire operation of cognitive radio rests. For cognitive radio to fulfill the potential it offers to solve the spectrum underutilization problem and do so in a reliable and computationally feasible manner, we require a spectrum sensor that detects spectrum holes (i.e., underutilized subbands of the radio spectrum), provides high spectral-resolution capability, estimates the average power in each subband of the spectrum, and identifies the unknown directions of interfering signals. Cyclostationarity is another desirable property that could be used for signal detection and classification. The multitaper method (MTM) for nonparametric spectral estimation accomplishes these tasks accurately, effectively, robustly, and in a computationally feasible manner. The objectives of this paper are to present: 1) tutorial exposition of the MTM, which is expandable to perform space-time processing and time-frequency analysis; 2) cyclostationarity, viewed from the Loeve and Fourier perspectives; and 3) experimental results, using Advanced Television Systems Committee digital television and generic land mobile radio signals, followed by a discussion of the effects of Rayleigh fading.

Do baseline glucocorticoids predict fitness

Abstract: Baseline glucocorticoid (cort) levels are increasingly employed as physiological indices of the relative condition or health of individuals and populations. Often, high cort levels are assumed to indicate an individual or population in poor condition and with low relative fitness (the Cort–Fitness Hypothesis). We review empirical support for this assumption, and find that variation in levels of baseline cort is positively, negatively, or non-significantly related to estimates of fitness. These relationships between levels of baseline cort and fitness can vary within populations and can even shift within individuals at different times in their life history. Overall, baseline cort can predict the relative fitness of individuals and populations, but the relationship is not always consistent or present.

Multi-agent systems in a distributed smart grid: Design and implementation

Abstract: The objective of this paper is to discuss the design and implementation of a multi-agent system that provides intelligence to a distributed smart grid — a smart grid located at a distribution level. A multi-agent application development will be discussed that involves agent specification, application analysis, application design and application realization. The message exchange in the proposed multi-agent system is designed to be compatible with an IP-based network (IP = Internet Protocol) which is based on the IEEE standard on Foundation for Intelligent Physical Agent (FIPA). The paper demonstrates the use of multi-agent systems to control a distributed smart grid in a simulated environment. The simulation results indicate that the proposed multi-agent system can facilitate the seamless transition from grid connected to an island mode when upstream outages are detected. This denotes the capability of a multi-agent system as a technology for managing the microgrid operation.

Quantitative, Qualitative, and Mixed Research Methods in Engineering Education

Abstract: The purpose of this research review is to open dialog about quantitative, qualitative, and mixed research methods in engineering education research. Our position is that no particular method is privileged over any other. Rather, the choice must be driven by the research questions. For each approach we offer a definition, aims, appropriate research questions, evaluation criteria, and examples from the Journal of Engineering Education. Then, we present empirical results from a prestigious international conference on engineering education research. Participants expressed disappointment in the low representation of qualitative studies; nonetheless, there appeared to be a strong preference for quantitative methods, particularly classroom-based experiments. Given the wide variety of issues still to be explored within engineering education, we expect that quantitative, qualitative, and mixed approaches will be essential in the future. We encourage readers to further investigate alternate research methods by accessing some of our sources and collaborating across education/social science and engineering disciplinary boundaries.

Influence of Ionic Strength, pH, and Cation Valence on Aggregation Kinetics of Titanium Dioxide Nanoparticles

Abstract: The extensive use of titanium dioxide nanoparticles (nano-TiO2) in many consumer products has raised concerns about possible risks to the environment. The magnitude of the threat may depend on whether nano-TiO2 remains dispersed in the environment, or forms much larger-sized aggregates or clusters. Currently, limited information is available on the issue. In this context, the purpose of the present article is to report initial measurements of the morphology and rate of formation of nano-TiO2 aggregates in aqueous suspensions as a function of ionic strength and of the nature of the electrolyte in a moderately acid to circumneutral pH range typical of soil and surface water conditions. Dynamic light scattering results show that 4−5 nm titanium dioxide particles readily form stable aggregates with an average diameter of 50−60 nm at pH ∼4.5 in a NaCl suspension adjusted to an ionic strength of 0.0045 M. Holding the pH constant, but increasing the ionic strength to 0.0165 M, leads to the formation of micron-si...

Co-opetition and Technological Innovation in Small and Medium-Sized Enterprises: A Multilevel Conceptual Model

Abstract: Small and Medium‐Sized Enterprises (SMEs) face tremendous challenges in their attempt to pursue technological innovations. This paper argues that co‐opetition strategy—simultaneous pursuit of compe...

Copy number analysis indicates monoclonal origin of lethal metastatic prostate cancer

Abstract: Many studies have shown that primary prostate cancers are multifocal and are composed of multiple genetically distinct cancer cell clones. Whether or not multiclonal primary prostate cancers typically give rise to multiclonal or monoclonal prostate cancer metastases is largely unknown, although studies at single chromosomal loci are consistent with the latter case. Here we show through a high-resolution genome-wide single nucleotide polymorphism and copy number survey that most, if not all, metastatic prostate cancers have monoclonal origins and maintain a unique signature copy number pattern of the parent cancer cell while also accumulating a variable number of separate subclonally sustained changes. We find no relationship between anatomic site of metastasis and genomic copy number change pattern. Taken together with past animal and cytogenetic studies of metastasis and recent single-locus genetic data in prostate and other metastatic cancers, these data indicate that despite common genomic heterogeneity in primary cancers, most metastatic cancers arise from a single precursor cancer cell. This study establishes that genomic archeology of multiple anatomically separate metastatic cancers in individuals can be used to define the salient genomic features of a parent cancer clone of proven lethal metastatic phenotype.

Mechanism of Mo-Dependent Nitrogenase

Abstract: Nitrogen-fixing bacteria catalyze the reduction of dinitrogen (N2) to two ammonia molecules (NH3), the major contribution of fixed nitrogen to the biogeochemical nitrogen cycle. The most widely studied nitrogenase is the molybdenum (Mo)-dependent enzyme. The reduction of N2 by this enzyme involves the transient interaction of two component proteins, designated the iron (Fe) protein and the MoFe protein, and minimally requires 16 magnesium ATP (MgATP), eight protons, and eight electrons. The current state of knowledge on how these proteins and small molecules together effect the reduction of N2 to ammonia is reviewed. Included is a summary of the roles of the Fe protein and MgATP hydrolysis, information on the roles of the two metal clusters contained in the MoFe protein in catalysis, insights gained from recent success in trapping substrates and inhibitors at the active-site metal cluster FeMo cofactor, and finally, considerations of the mechanism of N2 reduction catalyzed by nitrogenase.

Compressed sensing based interior tomography.

Abstract: While conventional wisdom is that the interior problem does not have a unique solution, by analytic continuation we recently showed that the interior problem can be uniquely and stably solved if we have a known sub-region inside a region of interest (ROI). However, such a known sub-region is not always readily available, and it is even impossible to find in some cases. Based on compressed sensing theory, here we prove that if an object under reconstruction is essentially piecewise constant, a local ROI can be exactly and stably reconstructed via the total variation minimization. Because many objects in computed tomography (CT) applications can be approximately modeled as piecewise constant, our approach is practically useful and suggests a new research direction for interior tomography. To illustrate the merits of our finding, we develop an iterative interior reconstruction algorithm that minimizes the total variation of a reconstructed image and evaluate the performance in numerical simulation.

The Life Course Perspective Applied to Families Over Time

Abstract: One of the enduring puzzles in the life sciences is the description and explanation of change over time. Such change is frequently called “development,” and the metaphors of growth and decline, gain and loss have often been employed to characterize change in structure or function of organisms over time. Cells, individuals, groups, and even social systems exhibit change over time. While most change is orderly, regular, and normative, some change is chaotic, irregular, and unpredicted. Growth or decline at the individual level often has antecedents or consequences at the collective group level.

Surrounded by mycobacteria: nontuberculous mycobacteria in the human environment.

Abstract: A majority of the Mycobacterium species, called the nontuberculous mycobacteria (NTM), are natural inhabitants of natural waters, engineered water systems, and soils. As a consequence of their ubiquitous distribution, humans are surrounded by these opportunistic pathogens. A cardinal feature of mycobacterial cells is the presence of a hydrophobic, lipid-rich outer membrane. The hydrophobicity of NTM is a major determinant of aerosolization, surface adherence, biofilm-formation, and disinfectant- and antibiotic resistance. The NTM are oligotrophs, able to grow at low carbon levels [>50 microg assimilable organic carbon (AOC) l(-1)], making them effective competitors in low nutrient, and disinfected environments (drinking water). Biofilm formation and oligotrophy lead to survival, persistence, and growth in drinking water distribution systems. In addition to their role as human and animal pathogens, the widespread distribution of NTM in the environment, coupled with their ability to degrade and metabolize a variety of complex hydrocarbons including pollutants, suggests that NTM may be agents of nutrient cycling.

Value Relevance of FAS 157 Fair Value Hierarchy Information and the Impact of Corporate Governance Mechanisms

Abstract: Statement of Financial Accounting Standards No. 157 (FAS 157), Fair Value Measurements, prioritizes the source of information used in fair value measurements into three levels: (1) Level 1 (observable inputs from quoted prices in active markets), (2) Level 2 (indirectly observable inputs from quoted prices of comparable items in active markets, identical items in inactive markets, or other market-related information), and (3) Level 3 (unobservable, firm-generated inputs). Using quarterly reports of banking firms in 2008, we find that the value relevance of Level 1 and Level 2 fair values is greater than the value relevance of Level 3 fair values. In addition, we find evidence that the value relevance of fair values (especially Level 3 fair values) is greater for firms with strong corporate governance. Overall, our results support the relevance of fair value measurements under FAS 157, but weaker corporate governance mechanisms may reduce the relevance of these measures.

Glaciers as a source of ancient and labile organic matter to the marine environment

Abstract: Riverineorganicmattersupportsoftheorderofone-fifthofestuarine metabolism 1 . Coastal ecosystems are therefore sensitive to alteration of both the quantity and lability of terrigenous dissolved organic matter (DOM) delivered by rivers. The lability of DOM is thought to vary with age, with younger, relatively unaltered organic matter being more easily metabolized by aquatic heterotrophs than older, heavily modified material 2–4 . This view is developed exclusively from workinwatershedswhereterrestrialplantandsoilsourcesdominate streamwaterDOM.Here wecharacterize streamwaterDOMfrom11 coastal watersheds on the Gulf of Alaska that vary widely in glacier coverage (0–64 per cent). In contrast to non-glacial rivers, we find that the bioavailability of DOM to marine microorganisms is significantlycorrelatedwithincreasing 14 Cage.Moreover,themostheavily glaciated watersheds are the source of the oldest ( 4kyr 14 C age) and mostlabile(66percentbioavailable)DOM.Theseglacialwatersheds haveextreme runoffrates,inpart becausetheyare subject tosomeof the highest rates of glacier volume loss on Earth 5 .W e estimate the cumulative flux of dissolved organic carbon derived from glaciers contributing runoff to the Gulf of Alaska at 0.13 60.01Tgyr 21 (1Tg 510 12 g), of which 0.10Tg is highly labile. This indicates that glacial runoff is a quantitatively important source of labile reduced carbon to marine ecosystems. Moreover, because glaciers and ice sheets represent the second largest reservoir of water in the global hydrologic system, our findings indicate that climatically driven changes in glacier volume could alter the age, quantity and reactivity of DOM entering coastal oceans. Biogeochemicalcycling in coastal marginsnear riverine outflows is dominated by the influx of terrestrial organic matter and nutrients. The effect of anthropogenic increases in nutrient export on sensitive systemsiswell-documentedinregionssuchastheGulfofMexicozone of hypoxia 6 . It is much less clear how climate-induced shifts in the exportofterrigenousDOMwillaffectcoastalenvironments,although the reactivity of this carbon will be key as the extent of its incorporationintomarinefoodwebsdependslargelyonitschemicalcharacter 7 .

Skin microbes on frogs prevent morbidity and mortality caused by a lethal skin fungus

Abstract: Emerging infectious diseases threaten human and wildlife populations. Altered ecological interactions between mutualistic microbes and hosts can result in disease, but an understanding of interactions between host, microbes and disease-causing organisms may lead to management strategies to affect disease outcomes. Many amphibian species in relatively pristine habitats are experiencing dramatic population declines and extinctions due to the skin disease chytridiomycosis, which is caused by the chytrid fungus Batrachochytrium dendrobatidis. Using a randomized, replicated experiment, we show that adding an antifungal bacterial species, Janthinobacterium lividum, found on several species of amphibians to the skins of the frog Rana muscosa prevented morbidity and mortality caused by the pathogen. The bacterial species produces the anti-chytrid metabolite violacein, which was found in much higher concentrations on frog skins in the treatments where J. lividum was added. Our results show that cutaneous microbes are a part of amphibians' innate immune system, the microbial community structure on frog skins is a determinant of disease outcome and altering microbial interactions on frog skins can prevent a lethal disease outcome. A bioaugmentation strategy may be an effective management tool to control chytridiomycosis in amphibian survival assurance colonies and in nature.

Measurement of the differential branching fraction and forward-backward asymmetry for B --> K(*)l+l-.

Abstract: We study B -> Kd(*)l(+)l(-) decays (l = e,u) based on a data sample of 657 x 10(6) B (B) over bar pairs collected with the Belle detector at the KEKB e(+)e(-) collider. We report the differential branching fraction, isospin asymmetry, K* polarization, and the forward-backward asymmetry (A(FB)) as functions of q(2) = M(ll)(2)c(2). The fitted A(FB) spectrum exceeds the standard model expectation by 2.7 standard deviations. The measured branching fractions are B(B -> K*l(+)l(-)) = (10: 7(-1.0)(+1.1)) x 10(-7) and B(B -> Kl(+)l(-)) = (4.8 (+0.5)(-0.4) +/- 0.3) x 10(-7), where the first errors are statistical and the second are systematic, with the muon to electron ratios R-K* = 0.83 +/- 0: 17 +/- 0.08 and R-K = 1.03 +/- 0.19 +/- 0.06.

Protein secretion systems in bacterial-host associations, and their description in the Gene Ontology

Abstract: Protein secretion plays a central role in modulating the interactions of bacteria with their environments. This is particularly the case when symbiotic bacteria (whether pathogenic, commensal or mutualistic) are interacting with larger host organisms. In the case of Gram-negative bacteria, secretion requires translocation across the outer as well as the inner membrane, and a diversity of molecular machines have been elaborated for this purpose. A number of secreted proteins are destined to enter the host cell (effectors and toxins), and thus several secretion systems include apparatus to translocate proteins across the plasma membrane of the host also. The Plant-Associated Microbe Gene Ontology (PAMGO) Consortium has been developing standardized terms for describing biological processes and cellular components that play important roles in the interactions of microbes with plant and animal hosts, including the processes of bacterial secretion. Here we survey bacterial secretion systems known to modulate interactions with host organisms and describe Gene Ontology terms useful for describing the components and functions of these systems, and for capturing the similarities among the diverse systems.

The virtual census: representations of gender, race and age in video games

Abstract: A large-scale content analysis of characters in video games was employed to answer questions about their representations of gender, race and age in comparison to the US population. The sample included 150 games from a year across nine platforms, with the results weighted according to game sales. This innovation enabled the results to be analyzed in proportion to the games that were actually played by the public, and thus allowed the first statements able to be generalized about the content of popular video games. The results show a systematic over-representation of males, white and adults and a systematic under-representation of females, Hispanics, Native Americans, children and the elderly. Overall, the results are similar to those found in television research. The implications for identity, cognitive models, cultivation and game research are discussed.

Multipolar spindle pole coalescence is a major source of kinetochore mis-attachment and chromosome mis-segregation in cancer cells.

Abstract: Many cancer cells display a CIN (Chromosome Instability) phenotype, by which they exhibit high rates of chromosome loss or gain at each cell cycle. Over the years, a number of different mechanisms, including mitotic spindle multipolarity, cytokinesis failure, and merotelic kinetochore orientation, have been proposed as causes of CIN. However, a comprehensive theory of how CIN is perpetuated is still lacking. We used CIN colorectal cancer cells as a model system to investigate the possible cellular mechanism(s) underlying CIN. We found that CIN cells frequently assembled multipolar spindles in early mitosis. However, multipolar anaphase cells were very rare, and live-cell experiments showed that almost all CIN cells divided in a bipolar fashion. Moreover, fixed-cell analysis showed high frequencies of merotelically attached lagging chromosomes in bipolar anaphase CIN cells, and higher frequencies of merotelic attachments in multipolar vs. bipolar prometaphases. Finally, we found that multipolar CIN prometaphases typically possessed γ-tubulin at all spindle poles, and that a significant fraction of bipolar metaphase/early anaphase CIN cells possessed more than one centrosome at a single spindle pole. Taken together, our data suggest a model by which merotelic kinetochore attachments can easily be established in multipolar prometaphases. Most of these multipolar prometaphase cells would then bi-polarize before anaphase onset, and the residual merotelic attachments would produce chromosome mis-segregation due to anaphase lagging chromosomes. We propose this spindle pole coalescence mechanism as a major contributor to chromosome instability in cancer cells.

On the eve of animal radiation: phylogeny, ecology and evolution of the Ediacara biota.

Abstract: Ediacara fossils document an important evolutionary episode just before the Cambrian explosion and hold critical information about the early evolution of macroscopic and complex multicellular life. They also represent an enduring controversy in paleontology. How are the Ediacara fossils related to living animals? How did they live? Do they share any evolutionary patterns with other life forms? Recent developments indicate that Ediacara fossils epitomize a phylogenetically diverse biosphere, probably including animals, protists, algae, fungi and others. Their simple ecology is dominated by epibenthic osmotrophs, deposit feeders and grazers, but few if any predators. Their evolution started with an early morphospace expansion followed by taxonomic diversification within confined morphospace, and concluded by extinction of many taxa at the Ediacaran–Cambrian boundary.

Challenges of PHEV penetration to the residential distribution network

Abstract: As Plug-in Hybrid Vehicles (PHEVs) take a greater share in the personal automobile market, their penetration levels may bring potential challenges to electric utility especially at the distribution level. This paper examines the impact of charging PHEVs on a distribution transformer under different charging scenarios. The simulation results indicate that at the PHEV penetration level of interest, new load peaks will be created, which in some cases may exceed the distribution transformer capacity. In order to keep the PHEVs from causing harmful new peaks, thus making the system more secure and efficient, several PHEV charging profiles are analyzed and some possible demand management solutions, including PHEV stagger charge and household load control, are explored.