bluuebunny/crossref_metadata_2025 huggingface dataset:
Catalysis in Solid Oxide Fuel Cells
Authors: Gorte R.J. , Vohs J.M.
Published: March 2011

Solid oxide fuel cells (SOFCs) and solid oxide electrolyzers (SOEs) hold much promise as highly efficient devices for the direct interconversion of chemical and electrical energy. Commercial application of these devices, however, requires further improvements in their performance and stability. Because the performance of SOFC and SOE electrodes depends on their microstructures, electronic and ionic conductivities, and chemical reactivities, the needed improvements require the expertise of various disciplines, with catalytic science playing an important role. Highly active and thermally stable catalysts are required to limit the internal losses in the devices, increase the range of fuels they can use, and decrease the temperatures at which they operate. In this article we review some of the most important recent advances in catalysis for SOFC and SOE electrodes and highlight additional improvements that are needed.
Fundamentals and Applications of Gas Hydrates
Authors: Koh Carolyn A. , Sloan E. Dendy , Sum Amadeu K. , Wu David T.
Published: March 2011

Fundamental understanding of gas hydrate formation and decomposition processes is critical in many energy and environmental areas and has special importance in flow assurance for the oil and gas industry. These areas represent the core of gas hydrate applications, which, albeit widely studied, are still developing as growing fields of research. Discovering the molecular pathways and chemical and physical concepts underlying gas hydrate formation potentially can lead us beyond flowline blockage prevention strategies toward advancing new technological solutions for fuel storage and transportation, safely producing a new energy resource from natural deposits of gas hydrates in oceanic and arctic sediments, and potentially facilitating effective desalination of seawater. The state of the art in gas hydrate research is leading us to new understanding of formation and dissociation phenomena that focuses on measurement and modeling of time-dependent properties of gas hydrates on the basis of their well-established thermodynamic properties.
Intensified Reaction and Separation Systems
Authors: Górak Andrzej , Stankiewicz Andrzej
Published: March 2011

Process intensification follows four main goals: to maximize the effectiveness of intra- and intermolecular events, to give each molecule the same processing experience, to optimize the driving forces/maximize specific interfacial areas, and to maximize the synergistic effects of partial processes. This paper shows how these goals can be reached in reaction and separation systems at all relevant time and length scales and is focused on the structuring of reactors and separation units, on the use of different energy forms to improve the reaction and separation, on combining and superimposing of different phenomena in one integrated unit or reactor, and on the application of oscillations for intensification of reaction and separation processes.
Metabolic Engineering for the Production of Natural Products
Authors: Pickens Lauren B. , Tang Yi , Chooi Yit-Heng
Published: March 2011

Natural products and their derivatives play an important role in modern healthcare as frontline treatments for many diseases and as inspiration for chemically synthesized therapeutics. With advances in sequencing and recombinant DNA technology, many of the biosynthetic pathways responsible for the production of these chemically complex yet valuable compounds have been elucidated. With an ever-expanding toolkit of biosynthetic components, metabolic engineering is an increasingly powerful method to improve natural product titers and generate novel compounds. Heterologous production platforms have enabled access to pathways from difficult to culture strains, systems biology and metabolic modeling tools have resulted in increasing predictive and analytic capabilities, advances in expression systems and regulation have enabled the fine-tuning of pathways for increased efficiency, and characterization of individual pathway components has facilitated the construction of hybrid pathways for the production of new compounds. These advances in the many aspects of metabolic engineering not only have yielded fascinating scientific discoveries but also make it an increasingly viable approach for the optimization of natural product biosynthesis.
Solubility of Gases and Liquids in Glassy Polymers
Authors: De Angelis Maria Grazia , Sarti Giulio C.
Published: March 2011

This review discusses a macroscopic thermodynamic procedure to calculate the solubility of gases, vapors, and liquids in glassy polymers that is based on the general procedure provided by the nonequilibrium thermodynamics for glassy polymers (NET-GP) method. Several examples are presented using various nonequilibrium (NE) models including lattice fluid (NELF), statistical associating fluid theory (NE-SAFT), and perturbed hard sphere chain (NE-PHSC). Particular applications illustrate the calculation of infinite-dilution solubility coefficients in different glassy polymers and the prediction of solubility isotherms for different gases and vapors in pure polymers as well as in polymer blends. The determination of model parameters is discussed, and the predictive abilities of the models are illustrated. Attention is also given to the solubility of gas mixtures and solubility isotherms in nanocomposite mixed matrices. The fractional free volume determined from solubility data can be used to correlate solute diffusivities in mixed matrices.
Tissue Engineering and Regenerative Medicine: History, Progress, and Challenges
Authors: Berthiaume François , Maguire Timothy J. , Yarmush Martin L.
Published: March 2011

The past three decades have seen the emergence of an endeavor called tissue engineering and regenerative medicine in which scientists, engineers, and physicians apply tools from a variety of fields to construct biological substitutes that can mimic tissues for diagnostic and research purposes and can replace (or help regenerate) diseased and injured tissues. A significant portion of this effort has been translated to actual therapies, especially in the areas of skin replacement and, to a lesser extent, cartilage repair. A good amount of thoughtful work has also yielded prototypes of other tissue substitutes such as nerve conduits, blood vessels, liver, and even heart. Forward movement to clinical product, however, has been slow. Another offshoot of these efforts has been the incorporation of some new exciting technologies (e.g., microfabrication, 3D printing) that may enable future breakthroughs. In this review we highlight the modest beginnings of the field and then describe three application examples that are in various stages of development, ranging from relatively mature (skin) to ongoing proof-of-concept (cartilage) to early stage (liver). We then discuss some of the major issues that limit the development of complex tissues, some of which are fundamentals-based, whereas others stem from the needs of the end users.
Animal Models of Neuropsychiatric Disorders
Authors: Fernando A.B.P. , Robbins T.W.
Published: March 2011

We survey the utility of animal models of mental illness, based on the identification of possible neurocognitive or neurobehavioral endophenotypes. Three broad clusters of neuropsychiatric disorder are discussed: (a) impulsive-compulsive syndromes, comprising drug addiction, attention deficit/hyperactivity disorder, gambling, obsessive-compulsive disorder, and compulsive eating; (b) disorders at the cognitive-emotional interface, comprising anxiety, depression, and schizophrenia; and (c) disorders purely of cognition, which contribute to the third cluster, cognitive disorders. The emphasis is thus on modeling symptoms rather than disorders per se. We also distinguish between two main aspects of any validated model: the precise neurobehavioral or neurocognitive processes implicated from detailed study of the clinical phenotype, and the perturbations, whether typically genetic, environmental, pharmacological, or neurodevelopmental, that are designed to simulate relevant neural, neurochemical, or molecular aspects of particular neuropsychiatric disorders.
Acute Stress Disorder Revisited
Authors: Cardeña Etzel , Carlson Eve
Published: March 2011

Acute stress disorder (ASD) was introduced into the Diagnostic and Statistical Manual (DSM) taxonomy in 1994 to address the lack of a specific diagnosis for acute pathological reactions to trauma and the role that dissociative phenomena play both in the short- and long-term reactions to trauma. In this review, we discuss the history and goals of the diagnosis and compare it with the diagnoses of acute stress reaction, combat stress reaction, and posttraumatic stress disorder (PTSD). We also evaluate the research on the validity and limitations of ASD as a diagnosis, the relationship between peritraumatic dissociation and other symptomatology, the extent to which PTSD is predicted by previous ASD or peritraumatic dissociation, and other important issues such as impairment and risk factors related to ASD. We conclude with our recommendations for changes in DSM-5 criteria and the development of more sophisticated research that considers ASD as but one of two or possibly three common acute posttraumatic syndromes.
Gene-Environment Interaction in Psychological Traits and Disorders
Authors: Dick Danielle M.
Published: March 2011

There has been an explosion of interest in studying gene-environment interactions (GxE) as they relate to the development of psychopathology. In this article, I review different methodologies to study gene-environment interaction, providing an overview of methods from animal and human studies and illustrations of gene-environment interactions detected using these various methodologies. Gene-environment interaction studies that examine genetic influences as modeled latently (e.g., from family, twin, and adoption studies) are covered, as well as studies of measured genotypes. Importantly, the explosion of interest in gene-environment interactions has raised a number of challenges, including difficulties with differentiating various types of interactions, power, and the scaling of environmental measures, which have profound implications for detecting gene-environment interactions. Taking research on gene-environment interactions to the next level will necessitate close collaborations between psychologists and geneticists so that each field can take advantage of the knowledge base of the other.
Resilience to Loss and Potential Trauma
Authors: Bonanno George A. , Westphal Maren , Mancini Anthony D.
Published: March 2011

Initial research on loss and potentially traumatic events (PTEs) has been dominated by either a psychopathological approach emphasizing individual dysfunction or an event approach emphasizing average differences between exposed and nonexposed groups. We consider the limitations of these approaches and review more recent research that has focused on the heterogeneity of outcomes following aversive events. Using both traditional analytic tools and sophisticated latent trajectory modeling, this research has identified a set of prototypical outcome patterns. Typically, the most common outcome following PTEs is a stable trajectory of healthy functioning or resilience. We review research showing that resilience is not the result of a few dominant factors, but rather that there are multiple independent predictors of resilient outcomes. Finally, we critically evaluate the question of whether resilience-building interventions can actually make people more resilient, and we close with suggestions for future research on resilience.
The Origins and Current Status of Behavioral Activation Treatments for Depression
Authors: Dimidjian Sona , Barrera Manuel , Martell Christopher , Muñoz Ricardo F. , Lewinsohn Peter M.
Published: March 2011

The past decade has witnessed a resurgence of interest in behavioral interventions for depression. This contemporary work is grounded in the work of Lewinsohn and colleagues, which laid a foundation for future clinical practice and science. This review thus summarizes the origins of a behavioral model of depression and the behavioral activation (BA) approach to the treatment and prevention of depression. We highlight the formative initial work by Lewinsohn and colleagues, the evolution of this work, and related contemporary research initiatives, such as that led by Jacobson and colleagues. We examine the diverse ways in which BA has been investigated over time and its emerging application to a broad range of populations and problems. We close with reflections on important directions for future inquiry.
Personality and Depression: Explanatory Models and Review of the Evidence
Authors: Klein Daniel N. , Kotov Roman , Bufferd Sara J.
Published: March 2011

Understanding the association between personality and depression has implications for elucidating etiology and comorbidity, identifying at-risk individuals, and tailoring treatment. We discuss seven major models that have been proposed to explain the relation between personality and depression, and we review key methodological issues, including study design, the heterogeneity of mood disorders, and the assessment of personality. We then selectively review the extensive empirical literature on the role of personality traits in depression in adults and children. Current evidence suggests that depression is linked to traits such as neuroticism/negative emotionality, extraversion/positive emotionality, and conscientiousness. Moreover, personality characteristics appear to contribute to the onset and course of depression through a variety of pathways. Implications for prevention and prediction of treatment response are discussed, as well as specific considerations to guide future research on the relation between personality and depression.
Sleep and Circadian Functioning: Critical Mechanisms in the Mood Disorders?
Authors: Harvey Allison G.
Published: March 2011

Evidence for the importance of sleep in the mood disorders has mushroomed over the past decade. Among adolescents and adults with a mood disorder, sleep disturbance is a risk factor for episodes, can contribute to relapse, has an adverse impact on emotion regulation, is critical for cognitive functioning, compromises health, and may contribute to substance use comorbidity and suicidality. This evidence has triggered a shift away from viewing sleep disturbance as an epiphenomenon, toward viewing sleep disturbance as an important but under-recognized mechanism in the multifactorial cause and maintenance of the mood disorders. Because the biology underpinning the sleep and circadian system is an open system, readily influenced by inputs from the environment, sleep in the mood disorders represents a unique and exciting domain for interdisciplinary research across behavioral, social, cognitive, and neurobiological levels of explanation. Together, the accumulated evidence has informed a range of novel, powerful, simple, and inexpensive treatments with potential for massive improvements to public health, including improving quality of life, reducing length and severity of episodes, and reducing the risk of subsequent episodes in the large number of individuals who suffer from mood disorders.
The Economic Analysis of Prevention in Mental Health Programs
Authors: Mihalopoulos Cathrine , Vos Theo , Pirkis Jane , Carter Rob
Published: March 2011

This article introduces the role economics can play in deciding whether programs designed to prevent mental disorders, which carry large disease and economic burdens, are a worthwhile use of limited healthcare resources. Fortunately, preventive interventions for mental disorders exist; however, which interventions should be financed is a common issue facing decision makers, and economic evaluation can provide answers. Unfortunately, existing economic evaluations of preventive interventions have limited applicability to local healthcare contexts. An approach to priority setting largely based on economic techniques—Assessing Cost-Effectiveness (ACE)—has been developed and used in Australia to answer questions regarding the economic credentials of competing interventions. Eleven preventive interventions for mental disorders and suicide, mostly psychological in nature, have been evaluated using this approach, with many meeting the criteria of good value for money. Interventions targeting the prevention of suicide, adult and childhood depression, childhood anxiety, and early psychosis have particular merit.
Psychologists and Detainee Interrogations: Key Decisions, Opportunities Lost, and Lessons Learned
Authors: Pope Kenneth S.
Published: March 2011

After the 9-11 terrorist attacks, U.S. psychologists faced hard choices about what roles, if any, were appropriate for psychologists in the detainee interrogations conducted in settings such as the Bagram Airbase, the Abu Ghraib Prison, and the Guantanamo Bay Detention Camps. The American Psychological Association (APA) sparked intense controversy with its policies and public statements. This article reviews APA decisions, documents, and public statements in this area, in the context of major criticisms and responses to those criticisms. The review focuses on key issues: how the APA created and reported policies in the areas of ethics and national security; transparency; psychologists' professional identities; psychologists' qualifications; ethical-legal conflicts; policies opposing torture; interpretations of avoiding harm; and effective interrogations. It suggests lessons learned, missed opportunities, and questions in need of a fresh approach.
Brain Graphs: Graphical Models of the Human Brain Connectome
Authors: Bullmore Edward T. , Bassett Danielle S.
Published: March 2011

Brain graphs provide a relatively simple and increasingly popular way of modeling the human brain connectome, using graph theory to abstractly define a nervous system as a set of nodes (denoting anatomical regions or recording electrodes) and interconnecting edges (denoting structural or functional connections). Topological and geometrical properties of these graphs can be measured and compared to random graphs and to graphs derived from other neuroscience data or other (nonneural) complex systems. Both structural and functional human brain graphs have consistently demonstrated key topological properties such as small-worldness, modularity, and heterogeneous degree distributions. Brain graphs are also physically embedded so as to nearly minimize wiring cost, a key geometric property. Here we offer a conceptual review and methodological guide to graphical analysis of human neuroimaging data, with an emphasis on some of the key assumptions, issues, and trade-offs facing the investigator.
Psychological Treatment of Chronic Pain
Authors: Kerns Robert D. , Sellinger John , Goodin Burel R.
Published: March 2011

Psychological treatment has emerged as a common component of a multidimensional and interdisciplinary plan of pain care for many persons with persistent pain. Treatments are informed by a biopsychosocial model of pain and a long history of psychological research that has identified the central role of behavioral, cognitive, and emotional factors that are believed to contribute to the perpetuation, if not the development, of chronic pain and pain-related disability and emotional distress. Empirically supported self-regulatory, behavioral, cognitive-behavioral, and acceptance and commitment interventions are reviewed, and current and future interventions are highlighted. Important issues related to individual differences and disparities in the experience of pain and pain treatment are discussed. In particular, race and ethnicity are considered, and special considerations for the management of pain in children and older adults are discussed.
Personality Disorders in Later Life: Questions About the Measurement, Course, and Impact of Disorders
Authors: Oltmanns Thomas F. , Balsis Steve
Published: March 2011

Lifespan perspectives have played a crucial role in shaping our understanding of many forms of psychopathology. Unfortunately, little attention has been given to personality disorders in middle adulthood and later life. Several issues are responsible for this deficiency, including difficulty applying the diagnostic criteria for personality disorders to older people and challenges in identifying appropriate samples of older participants. The goal of this review is to explore the benefits of considering older adults in the study of personality disorders. Later life offers a unique opportunity for investigators to consider links between personality pathology and consequential outcomes in people's lives. Many domains are relevant, including health, longevity, social adjustment, marital relationships, and the experience of major life events. We review each domain and consider ways in which the study of middle-aged and older adults challenges researchers to evaluate how personality disorders in general are defined and measured.
Angle-Resolved Photoemission Studies of Quantum Materials
Authors: Lu Donghui , Vishik Inna M. , Yi Ming , Chen Yulin , Moore Rob G. , Shen Zhi-Xun
Published: March 2011

Angle-resolved photoemission spectroscopy (ARPES) has emerged as a leading experimental probe for studying the complex phenomena in quantum materials, a subject of increasing importance. The power of this technique stems from the directness and the richness of the momentum-resolved information it can provide, such as band dispersion, Fermi surface topology, and electron self-energy. Over the past decade, the significantly improved energy and momentum resolution and carefully matched experiments have turned this technique into a sophisticated tool in characterizing the electronic structure of complex materials. This revolution is mostly evident in the study of cuprate high-temperature superconductors. More recently, this technique has played a critical role in advancing our understanding of the newly discovered iron-based superconductors and topological insulators. In this paper we review some of the recent ARPES results and discuss the future perspective in this rapidly developing field.
Bose Gases with Nonzero Spin
Authors: Ueda Masahito
Published: March 2011

Gaseous Bose-Einstein condensates with nonzero spin feature multicomponent order parameters that reflect the internal degrees of freedom. They exhibit a rich variety of superfluid and magnetic phenomena similar or complementary to those of superfluid helium-3. The unprecedented degree of manipulability of atomic gases makes spinor condensates a unique playground for exploring symmetry breaking, topological excitations, and the interplay between superfluidity and magnetism. An overview of these subjects is provided.
Strong Correlations from Hund’s Coupling
Authors: Georges Antoine , Medici Luca de' , Mravlje Jernej
Published: March 2011

Strong electronic correlations are often associated with the proximity of a Mott-insulating state. In recent years however, it has become increasingly clear that the Hund’s rule coupling (intra-atomic exchange) is responsible for strong correlations in multiorbital metallic materials that are not close to a Mott insulator. Hund’s coupling has two effects: It influences the energetics of the Mott gap and strongly suppresses the coherence scale for the formation of a Fermi liquid. A global picture has emerged recently, which emphasizes the importance of the average occupancy of the shell as a control parameter. The most dramatic effects occur away from half-filling or single occupancy. We review the theoretical understanding and physical properties of these Hund’s metals, together with the relevance of this concept to transition-metal oxides (TMOs) of the 3d, and especially 4d, series (such as ruthenates), as well as to the iron-based superconductors (iron pnictides and chalcogenides).
Spin Ice, Fractionalization, and Topological Order
Authors: Castelnovo C. , Moessner R. , Sondhi S.L.
Published: March 2011

The spin ice compounds Dy2Ti2O7 and Ho2Ti2O7 are highly unusual magnets that epitomize a set of concepts of great interest in modern condensed matter physics: Their low-energy physics exhibits an emergent gauge field and their excitations are magnetic monopoles that arise from the fractionalization of the microscopic magnetic spin degrees of freedom. In this review, we provide an elementary introduction to these concepts and we survey the thermodynamics, statics, and dynamics—in and out of equilibrium—of spin ice from these vantage points. Along the way, we touch on topics such as emergent Coulomb plasmas, observable Dirac strings, and irrational charges. We close with the outlook for these unique materials.
Magnetoelectric Hexaferrites
Authors: Kimura Tsuyoshi
Published: March 2011

Magnetoelectric (ME) multiferroics are materials that combine coupled electric and magnetic dipoles. Studies of ME multiferroics are a time-honored research subject because of their potential for future electronic devices. Recent discoveries have revealed that ferroelectricity can be induced by complex internal arrangements of magnetic moments. This new family of multiferroics is called magnetically induced ferroelectrics. Magnetically induced ferroelectrics are known to show giant ME effects, i.e., changes in ferroelectric polarization upon application of an external magnetic field. However, their ME effects usually occur at temperatures that are too low and at applied external fields (> ∼0.1 T) that are too high to be of practical use. Thus, the quest for a robust room-temperature ME effect is a major challenge in ME research. Lately, some ferrites with hexagonal crystal structures, termed hexaferrites, have been found to show ME effects at room temperature and low magnetic fields (∼0.01 T). The results represented an important step toward practical applications using the ME effect in magnetically induced ferroelectrics. This review introduces structure, magnetism, and resulting magnetoelectricity of hexaferrite systems, which are promising candidate materials for ME devices.
Physics of Cancer: The Impact of Heterogeneity
Authors: Zhang Qiucen , Austin Robert H.
Published: March 2011

It is a common mistake to view cancer as a single disease with a single possible cure which we have just not found yet. In reality cancer takes on many forms that share a common symptom: uncontrolled cell growth and successful invasion of cancer colonies to remote regions of the body. The key reason why we may never be able to defeat cancer may lie in the extreme heterogeneity of the population of the cells in a tumor: there is no one magic bullet. We will try in this review to show how the developing field of the physics of biological heterogeneity can help us understand and quantify the emergent heterogeneity that makes cancer such a fundamental puzzle.
Physics of Cardiac Arrhythmogenesis
Authors: Karma Alain
Published: March 2011

A normal heartbeat is orchestrated by the stable propagation of an excitation wave that produces an orderly contraction. In contrast, wave turbulence in the ventricles, clinically known as ventricular fibrillation (VF), stops the heart from pumping and is lethal without prompt defibrillation. I review experimental, computational, and theoretical studies that have shed light on complex dynamical phenomena linked to the initiation, maintenance, and control of wave turbulence. I first discuss advances made to understand the precursor state to a reentrant arrhythmia where the refractory period of cardiac tissue becomes spatiotemporally disordered; this is known as an arrhythmogenic tissue substrate. I describe observed patterns of transmembrane voltage and intracellular calcium signaling that can contribute to this substrate, and symmetry breaking instabilities to explain their formation. I then survey mechanisms of wave turbulence and discuss novel methods that exploit electrical pacing stimuli to control precursor patterns and low-energy pulsed electric fields to control turbulence.
Sixty Years of Condensed Matter Physics: An Everlasting Adventure
Authors: Nozières Philippe
Published: March 2011

Condensed matter physics has changed since the fifties: I attempt to retrace its evolution in the light of my own trajectory. It was and it remains a living field, in constant renewal. New ideas, new concepts keep appearing along with new experimental and theoretical tools. The danger lies in the bureaucratic evolution of scientific research, which might sterilize imagination and innovation. The future lies in the hands of young physicists who should defend their independence and creativity against fashions and competition.
Quantum Coherence in Photosynthetic Light Harvesting
Authors: Ishizaki Akihito , Fleming Graham R.
Published: March 2011

Recent two-dimensional (2D) electronic spectroscopic experiments revealed that electronic energy transfer in photosynthetic light harvesting involves long-lived quantum coherence among electronic excitations of pigments. These findings have led to the suggestion that quantum coherence might play a role in achieving the remarkable quantum efficiency of photosynthetic light harvesting. Further, this speculation has led to much effort being devoted to elucidation of the quantum mechanisms of the photosynthetic excitation energy transfer (EET). In this review, we provide an overview of recent experimental and theoretical investigations of photosynthetic electronic energy transfer, specifically addressing underlying mechanisms of the observed long-lived coherence and its potential roles in photosynthetic light harvesting. We close with some thoughts on directions for future developments in this area.
Correlated Quantum Phenomena in the Strong Spin-Orbit Regime
Authors: Witczak-Krempa William , Chen Gang , Kim Yong Baek , Balents Leon
Published: March 2011

We discuss phenomena arising from the combined influence of electron correlation and spin-orbit coupling (SOC), with an emphasis on emergent quantum phases and transitions in heavy transition metal compounds with 4d and 5d elements. A common theme is the influence of spin-orbital entanglement produced by SOC, which influences the electronic and magnetic structure. In the weak-to-intermediate correlation regime, we show how nontrivial band-like topology leads to a plethora of phases related to topological insulators (TIs). We expound these ideas using the example of pyrochlore iridates, showing how many novel phases, such as the Weyl semimetal, axion insulator, topological Mott insulator, and TIs, may arise in this context. In the strong correlation regime, we argue that spin-orbital entanglement fully or partially removes orbital degeneracy, reducing or avoiding the normally ubiquitous Jahn-Teller effect. As we illustrate for the honeycomb-lattice iridates and double perovskites, this leads to enhanced quantum fluctuations of the spin-orbital entangled states and the chance to promote exotic spin liquid and multipolar ordered ground states. Connections to experiments, materials, and future directions are discussed.
Deep Mantle Seismic Modeling and Imaging
Authors: Lay Thorne , Garnero Edward J.
Published: March 2011

Detailed seismic modeling and imaging of Earth's deep interior is providing key information about lower-mantle structures and processes, including heat flow across the core-mantle boundary, the configuration of mantle upwellings and downwellings, phase equilibria and transport properties of deep mantle materials, and mechanisms of core-mantle coupling. Multichannel seismic wave analysis methods that provide the highest-resolution deep mantle structural information include network waveform modeling and stacking, array processing, and 3D migrations of P- and S-wave seismograms. These methods detect and identify weak signals from structures that cannot be resolved by global seismic tomography. Some methods are adapted from oil exploration seismology, but all are constrained by the source and receiver distributions, long travel paths, and strong attenuation experienced by seismic waves that penetrate to the deep mantle. Large- and small-scale structures, with velocity variations ranging from a fraction of a percent to tens of percent, have been detected and are guiding geophysicists to new perspectives of thermochemical mantle convection and evolution.
Early Silicate Earth Differentiation
Authors: Caro Guillaume
Published: March 2011

The discovery of small142Nd anomalies in early Archean rocks has brought about a revolution in our understanding of early planetary differentiation processes.142Nd is a radiogenic isotope produced by the decay of now-extinct146Sm in crustal and mantle reservoirs. Given that142Nd heterogeneities can be produced only prior to 4.2 Gya, this short-lived chronometer provides selective information on the very early evolution of primordial silicate reservoirs. This information is particularly crucial for Earth, where the fingerprints of the earliest crustal formation processes have been almost entirely erased from the geological record. This article reviews the history of the field, from the pioneering applications of the147Sm-143Nd and146Sm-142Nd systems to ancient crustal rocks, to the more recent insights gained from application of146Sm-142Nd to meteorites and lunar samples.
Soft Tissue Preservation in Terrestrial Mesozoic Vertebrates
Authors: Schweitzer Mary Higby
Published: March 2011

Exceptionally preserved fossils—i.e., those that retain, in some manner, labile components of organisms that are normally degraded far too quickly to enter the fossil record—hold the greatest potential for understanding aspects of the biology of long-extinct animals and are the best targets for the search for endogenous biomolecules. Yet the modes of preservation of these labile components, and exactly what remains of the original composition, are not well understood. Here, I review a selection of cases of soft tissue preservation in Mesozoic vertebrates, examine chemical and environmental factors that may influence such preservation, explore the potential of these fossils for high-resolution analytical studies, and suggest clarification of terminologies and criteria for determining the endogeneity of source and the degree of preservation of these well-preserved tissues.
Using Time-of-Flight Secondary Ion Mass Spectrometry to Study Biomarkers
Authors: Thiel Volker , Sjövall Peter
Published: March 2011

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) is a technique designed to analyze the composition and spatial distribution of molecules and chemical structures on surfaces. These capabilities have generated much interest in its use in geobiology, in particular for the characterization of organic biomarkers (molecular biosignatures) at the microscopic level. We here discuss the strengths, weaknesses, and potential of ToF-SIMS for biomarker analyses with a focus on applications in geobiology, including biogeochemistry, organic geochemistry, geomicrobiology, and paleobiology. After describing the analytical principles of ToF-SIMS, we discuss issues of biomarker spectral formation and interpretation. Then, key applications of ToF-SIMS to soft (microbial matter, cells), hard (microbial mineral precipitates), and liquid (petroleum) samples relevant in geobiology are reviewed. Finally, we examine the potential of ToF-SIMS in biomarker research and the current limitations and obstacles for which further development would be beneficial to the field.
Evolution of Grasses and Grassland Ecosystems
Authors: Strömberg Caroline A.E.
Published: March 2011

The evolution and subsequent ecological expansion of grasses (Poaceae) since the Late Cretaceous have resulted in the establishment of one of Earth's dominant biomes, the temperate and tropical grasslands, at the expense of forests. In the past decades, several new approaches have been applied to the fossil record of grasses to elucidate the patterns and processes of this ecosystem transformation. The data indicate that the development of grassland ecosystems on most continents was a multistage process involving the Paleogene appearance of (C3and C4) open-habitat grasses, the mid-late Cenozoic spread of C3grass-dominated habitats, and, finally, the Late Neogene expansion of C4grasses at tropical-subtropical latitudes. The evolution of herbivores adapted to grasslands did not necessarily coincide with the spread of open-habitat grasses. In addition, the timing of these evolutionary and ecological events varied between regions. Consequently, region-by-region investigations using both direct (plant fossils) and indirect (e.g., stable carbon isotopes, faunas) evidence are required for a full understanding of the tempo and mode of grass and grassland evolution.
Slow Earthquakes and Nonvolcanic Tremor
Authors: Beroza Gregory C. , Ide Satoshi
Published: March 2011

Nonvolcanic tremor is observed in close association with geodetically observed slow-slip events in subduction zones. Accumulating evidence points to these events as members of a family of slow earthquakes that occur as shear slip on the downdip extensions of fault zones in a regime that is transitional between a frictionally locked region above and a freely slipping region below. By virtue of their locations and their properties, slow earthquakes are certain to provide new insights into the behavior of earthquakes and faulting and into the hazard they embody.
Long-Term Ecological Records and Their Relevance to Climate Change Predictions for a Warmer World
Authors: Willis K.J. , MacDonald G.M.
Published: March 2011

This review focuses on biotic responses during intervals of time in the fossil record when the magnitude and rate of climate change exceeded or were comparable with those predicted to occur in the next century ( Solomon et al. 2007 ). These include biotic responses during: (a) the Paleo-Eocene Thermal Maximum and early Eocene Climatic Optimum, (b) the mid-Pliocene warm interval, (c) the Eemian, and (d) the most recent glacial-interglacial transition into the Holocene. We argue that although the mechanisms responsible for these past changes in climate were different (i.e., natural processes rather than anthropogenic), the rate and magnitude of climate change were often similar to those predicted for the next century and therefore highly relevant to understanding future biotic responses. In all intervals we examine the fossil evidence for the three most commonly predicted future biotic scenarios, namely, extirpation, migration (in the form of a permanent range shift), or adaptation. Focusing predominantly on the terrestrial plant fossil record, we find little evidence for extirpation during warmer intervals; rather, range shifts, community turnover, adaptation, and sometimes an increase in diversity are observed.
Phylogenetic Methods in Biogeography
Authors: Ronquist Fredrik , Sanmartín Isabel
Published: March 2011

Phylogenetic approaches to biogeography are rapidly becoming more sophisticated. Four types of models are being explored in the literature: (a) diffusion models, (b) island models, (c) hierarchical vicariance models (HVMs), and (d) reticulate models. Diffusion models are used primarily for phylogeographic inference but can also offer insights into geographic discontinuities of significance on longer time scales. For the island models, statistical approaches are now well developed and typically offer more detailed insight than parsimony analysis. In contrast, parsimony may still be the best option for HVM analysis, because existing statistical approaches do not yet accommodate dispersal. The proposed probabilistic models of reticulate scenarios remain poorly understood, even though they may currently do the best job of integrating diversification processes into biogeographic analysis. Statistical approaches are gaining in popularity across the field, in part because of the flexibility of stochastic modeling. This allows investigators to address important related processes, such as ecological interactions and climate change, in biogeographic inference.
On the Use of Stable Isotopes in Trophic Ecology
Authors: Boecklen William J. , Yarnes Christopher T. , Cook Bethany A. , James Avis C.
Published: March 2011

Stable isotope analysis (SIA) has proven to be a useful tool in reconstructing diets, characterizing trophic relationships, elucidating patterns of resource allocation, and constructing food webs. Consequently, the number of studies using SIA in trophic ecology has increased exponentially over the past decade. Several subdisciplines have developed, including isotope mixing models, incorporation dynamics models, lipid-extraction and correction methods, isotopic routing models, and compound-specific isotopic analysis. As with all tools, there are limitations to SIA. Chief among these are multiple sources of variation in isotopic signatures, unequal taxonomic and ecosystem coverage, over-reliance on literature values for key parameters, lack of canonical models, untested or unrealistic assumptions, low predictive power, and a paucity of experimental studies. We anticipate progress in SIA resulting from standardization of methods and models, calibration of model parameters through experimentation, and continued development of several recent approaches such as isotopic routing models and compound-specific isotopic analysis.
The Behavioral Ecology of Nutrient Foraging by Plants
Authors: Cahill James F. , McNickle Gordon G.
Published: March 2011

Foraging for resources influences ecological interactions among individuals and species, regardless of taxonomic affiliation. Here we review studies of nutrient foraging in plants, with an emphasis on how nutritious and non-nutritious cues in the soil alter behavioral decisions and patterns of root placement. Three patterns emerge: (a) Plants alter root placement in response to many diverse cues; (b) species respond differently to these cues; and (c) there are nonadditive responses to multiple cues, indicating that plants exhibit complex multidimensional root foraging strategies. We suggest that this complexity calls for novel approaches to understanding nutrient foraging by plants. Resource selection functions are commonly used by animal behaviorists and may be useful to describe plant foraging strategies. Understanding such approaches may allow researchers to link individual behavior to population and community dynamics.
Climate Relicts: Past, Present, Future
Authors: Hampe Arndt , Jump Alistair S.
Published: March 2011

Populations left behind during climate-driven range shifts can persist in enclaves of benign environmental conditions within an inhospitable regional climate. Such climate relicts exist in numerous plant and animal species worldwide, yet our knowledge of them is fragmented and lacks a general framework. Here we synthesize the empirical evidence considering (a) relict habitats, (b) abiotic and biotic constraints on population dynamics, (c) mechanisms promoting population persistence, and (d) uncertainties concerning their future prospects. We identify three major types of climate relicts: (a) those constrained primarily by climate-driven abiotic factors, (b) those restricted to areas that are inaccessible to antagonistic species for climatic reasons, and (c) those requiring a host or mutualistic species that is itself limited by climate. Understanding the formation and functioning of climate relicts is essential for their conservation and for our understanding of the response of species and populations to climate change.
Ehrlich and Raven Revisited: Mechanisms Underlying Codiversification of Plants and Enemies
Authors: Janz Niklas
Published: March 2011

After almost 50 years of scrutiny, the ideas that Ehrlich and Raven presented in their classical paper on the coevolution between butterflies and plants are still very much alive. Much of this interest has involved the potential for codiversification, both in how the interaction itself diversifies and how the interaction affects modes and rates of speciation. Despite high levels of conservatism and specialization, diversification of the interaction appears to be mainly a consequence of host shifts, but this somewhat paradoxical conclusion can be understood by an appreciation of the ecological as well as genetic mechanisms behind host shifts. There are several ways that the interaction can influence speciation, with or without host-plant-based divergent selection on reproductive barriers. One current debate is over the relative importance of radiations following shifts to new adaptive zones and elevated rates of speciation in groups with plastic and diverse host use.
Evolution of Anopheles gambiae in Relation to Humans and Malaria
Authors: White Bradley J. , Collins Frank H. , Besansky Nora J.
Published: March 2011

The closely related and morphologically indistinguishable mosquito species in the Afrotropical Anopheles gambiae complex differ dramatically in their contribution to malaria transmission, ranging from major vectors through minor or locally important vectors and nonvectors. Radiation of the A. gambiae complex and ongoing diversification within its nominal species appears to be a product of recent and rapid adaptation to environmental heterogeneities, notably those of anthropogenic origin. Polytene chromosome and genomic analyses suggest that paracentric chromosomal inversions and possibly other low-recombination regions have played instrumental roles in this process by facilitating ecotypic differentiation both within and across semipermeable species boundaries. Forthcoming complete genome sequences from several members of the A. gambiae complex will provide powerful tools to accelerate ongoing investigation of how genetic diversification of populations and species has shaped behavioral and physiological traits, such as vector competence, that bear on vectorial importance.
Functional Ecology of Free-Living Nitrogen Fixation: A Contemporary Perspective
Authors: Reed Sasha C. , Cleveland Cory C. , Townsend Alan R.
Published: March 2011

Nitrogen (N) availability is thought to frequently limit terrestrial ecosystem processes, and explicit consideration of N biogeochemistry, including biological N2 fixation, is central to understanding ecosystem responses to environmental change. Yet, the importance of free-living N2 fixation—a process that occurs on a wide variety of substrates, is nearly ubiquitous in terrestrial ecosystems, and may often represent the dominant pathway for acquiring newly available N—is often underappreciated. Here, we draw from studies that investigate free-living N2 fixation from functional, physiological, genetic, and ecological perspectives. We show that recent research and analytical advances have generated a wealth of new information that provides novel insight into the ecology of N2 fixation as well as raises new questions and priorities for future work. These priorities include a need to better integrate free-living N2 fixation into conceptual and analytical evaluations of the N cycle's role in a variety of global change scenarios.
Native Pollinators in Anthropogenic Habitats
Authors: Winfree Rachael , Bartomeus Ignasi , Cariveau Daniel P.
Published: March 2011

Animals pollinate 87% of the world's flowering plant species. Therefore, how pollinators respond to human-induced land-use change has important implications for plants and the species that depend on them. Here, we synthesize the published literature on how land-use change affects the main groups of pollinators: bees, butterflies, flies, birds, and bats. Responses to land-use change are predominantly negative but are highly variable within and across taxa. The directionality of pollinator response varies according to study design, with comparisons across gradients in surrounding landscape cover finding largely negative responses and comparisons across local land-use types finding largely positive responses. Furthermore, among the studies using landscape designs, most were performed in systems where land-use change is extreme, and such studies find stronger negative effects than those performed in more moderate systems. Across multiple taxa, dietary specialists show greater sensitivity to land use than do generalists. There is a need for studies of pollinator species composition and relative abundance, rather than simply species richness and aggregate abundance, to identify the species that are lost and gained with increasing land-use change.