bluuebunny/crossref_metadata_2025 huggingface dataset:
An Improved Alternative to the Three-Dimensional, Swash Plate Mechanism
Authors: Shoup T. E. , Chi D.
Published: November 2009

This paper presents a theoretical analysis and a design technique for the use of a special type of adjustable spatial slider crank mechanism to replace the swash plate device commonly used as a variable displacement pump or compressor. This paper is an extension of a previous research effort utilizing the RSSP mechanism [7] and considers the influence of geometric proportions of a device on stroke size, velocity fluctuation, and force transmission effectiveness. The device is shown to have significant kinematic advantages over the traditional form of the swash plate mechanism. Design curves are presented and an example application is provided.
Minimization of Inertia-Induced Forces in Spherical Four-Bar Mechanisms. Part 2: Wobble-Plate Engines
Authors: Gill G. S. , Freudenstein F.
Published: November 2009

In Part 2 of this paper, computer-aided design procedures have been developed for the optimum mass distribution of high-speed wobble-plate engines.
Planar and Spatial Rigid Motion as Special Cases of Spherical and 3-Spherical Motion
Authors: McCarthy J. M.
Published: November 2009

This paper examines spherical and 3-spherical rigid motions with instantaneous invariants approaching zero. It is shown that these motions may be identified with planar and spatial motion, respectively. The instantaneous invariants are ratios of arc-length along the surface of the sphere to its radius, thus the process of shrinking their value may be viewed as expanding the sphere while bounding the instantaneous displacements on the sphere. This allows a smooth transformation of the results of the curvature theory of spherical and 3-spherical motion into their planar and spatial counterparts.
Atmospheric Sulfur in Archean Komatiite-Hosted Nickel Deposits
Authors: Bekker Andrey , Barley Mark E. , Fiorentini Marco L. , Rouxel Olivier J. , Rumble Douglas , Beresford Stephen W.
Published: November 2009

Early Ore Formation

Ore deposits contain most of the world's metal resources, from commonly used metals such as iron, to precious and expensive metals such as platinum. Understanding how these ancient deposits form may lead to more efficient metal extraction and give clues about early Earth.

Bekker
et al.

(p.
1086
) studied sulfur and iron isotopes in 2.7-billion-year old Fe-Ni sulfide deposits from Canada and Australia and found that most of the metal-scavenging sulfur was originally atmospheric in origin. Photochemical reactions in the ancient oxygen-free atmosphere produced sulfide that eventually circulated to the sea floor and mixed with newly erupted komatite magmas. Thus, global surface processes in the oceans, atmosphere, and on continents are geochemically linked to ore-forming processes within Earth.
The Hotter the Engine, the Better
Authors: Perepezko John H.
Published: November 2009

Alloys based on molybdenum or niobium may allow the high-temperature components of jet engines to run hotter and more efficiently.
Pleistocene Megafaunal Collapse, Novel Plant Communities, and Enhanced Fire Regimes in North America
Authors: Gill Jacquelyn L. , Williams John W. , Jackson Stephen T. , Lininger Katherine B. , Robinson Guy S.
Published: November 2009

Demise of the Megafauna

Approximately 10,000 years ago, the Pleistocene-Holocene deglaciation in North America produced widespread biotic and environmental change, including extinctions of megafauna, reorganization of plant communities, and increased wildfire. The causal links and sequences of these changes remain unclear.

Gill
et al.

(p.
1100
; see the Perspective by

Johnson

) unravel these connections in an analysis of pollen, charcoal, and the dung fungus
Sporormiella
from the sediments of Appleman Lake, Indiana. The decline in Pleistocene megafaunal population densities (inferred from fungal spore abundances) preceded both the formation of the lateglacial plant communities and a shift to an enhanced fire regime, thus contradicting hypotheses that invoke habitat change or extraterrestrial impact to explain the megafaunal extinction. The data suggest that population collapse and functional extinction of the megafauna preceded their final extinction by several thousand years.
Governance of Both Poles
Authors: Grimaldi Albert
Published: November 2009

At the end of this month, the Antarctic Treaty Summit in Washington, DC, will celebrate the 50th anniversary of an international agreement that has been centered around science, promoting cooperation to manage nearly 10% of Earth for peaceful purposes since 1 December 1959 (see
www.atsummit50.aq
). As the world moves toward negotiating effective policies related to climate change, lessons from the Antarctic Treaty experience can be drawn upon, particularly in regard to the future governance of international spaces that are considered to have an amplified response to climate change. Among the most critical are the Arctic regions.
Splitting the Difference Between Oil Pessimists and Optimists
Authors: Kerr Richard A.
Published: November 2009

World production of conventional oil is likely to peak before 2030 and could reach its limits before 2020, a major report from a new voice in the debate over oil depletion warns. In view of the daunting task of weaning the world's transportation off oil, the risk of a peak before 2030 "needs to be given serious consideration," the report says.
Chloroplast Shuffle
Authors: Pennisi Elizabeth
Published: November 2009

Chloroplasts seem to rely on the polymerization of protein filaments to make their way across a cell, researchers reported at the 9th International Plant Molecular Biology Congress, and they can move quickly—or slowly—depending on the circumstances.
Isolation and Identification of an Atypical Aeromonas salmonicida Strain Causing Epizootic Losses Among Atlantic Salmon (Salmo salar) Reared in a Nova Scotian Hatchery
Authors: Paterson W. D. , Douey D. , Desautels D.
Published: November 2009

The bacterium causing 50% cumulative mortality among postyearling parr (pyp) Atlantic salmon (Salmo salar) reared at a Nova Scotian hatchery was identified to be an atypical, achromogenic Aeromonas salmonicida strain. This organism, although differing in several biochemical reactions from typical A. salmonicida, was sensitive to A. salmonicida bacteriophages. Antigenically, the Kejimkujik A. salmonicida was indistinguishable from typical A. salmonicida strains when the serological relatedness was examined using cross-adsorbed rabbit antisera. Analysis of DNA from the atypical A. salmonicida yielded a % GC value of 57.85, a value within the range expected for A. salmonicida.Key words: atypical, Aeromonas salmonicida, Atlantic salmon
Differential Prey Vulnerability and Predator Selectivity: Effects of Evasive Prey on Bluegill (Lepomis macrochirus) and Pumpkinseed (L. gibhosus) Predation
Authors: Vinyard Gary L.
Published: November 2009

Sunfish will select Daphnia preferentially over copepods even though the apparent size of the copepods may be considerably larger. This selectivity is probably the result of the fishes having learned differences in the evasion capabilities of the two different prey types, and having translated this into a differential selectivity. Sunfish have the ability to correlate information about the evasion capabilities of prey with visual appearances of the prey, and to select less evasive prey. Such information may have considerable significance in defining the observed selectivity of these fish in nature, and such behavioral responses should be considered in future modeling efforts.Key words: predation, Lepomis, selectivity, behavior
Stable Cycles in Multistage Recruitment Models: An Application to the Northern California Dungeness Crab (Cancer magister) Fishery
Authors: McKelvey R. , Hankin D. , Yanosko K. , Snygg C.
Published: November 2009

This study illustrates, through the modeling of the Northern California Dungeness crab fishery, a diagnostic approach to the inference of multistage density-dependent recruitment mechanisms operating in animal populations. Northern California Dungeness crab landings have exhibited a strikingly regular cycling pattern since the early 1940s, but with increasing amplitude swings as the fishery has expanded suggesting the possibility of an eventual crash. A variety of mechanisms have been proposed, involving either biological feedback controls or exogeneous environmental effects, to account for the regular cycling and its possible destabilization by fishing. This study examines the plausibility of various alternative biological control mechanisms by incorporating them, one by one, into a multistage dynamic recruitment model, of nonlinear renewal type, based on general qualitative features of the crustacean's life history. A total of 48 plausible model variants are examined, reflecting differences in intensity and timing of possible feedback controls and uncertainty about exploitation and survival rates.Model analysis incorporates two complementary approaches to test out the range of alternative hypotheses incorporated in these variants. The first approach is based on examination of qualitative features of model dynamics: period and amplitude of stable cycles, and the model's response to varying levels of exploitation. The second is based upon extracted estimates of probable historic year-class strength and assesses the fit of model variants by least-squares regression techniques. These twin diagnostic procedures allow elimination of most model variants, and support the hypothesis that recruitment must be determined in the very early life stages, egg, or larval.The last phase of analysis is to further probe the model by numerical experimentation, including a simulation of the institution of female harvest. Finally, the implications of the modeling exercise are drawn, for future field studies and for second generation modelling.Key words: bifurcations, Dungeness crab, Cancer magister, stable cycles, multistage recruitment models, stock-recruitment
Acoustically Derived Estimate of the Size Distribution for a Sample of Sperm Whales (Physeter catodon) in the Western North Atlantic
Authors: Adler-Fenchel Hilary S.
Published: November 2009

Acoustic determination of sperm whale length based on measurement of the interpulse interval (IPI) of the characteristic multipulse sound click was used on a sample of 4000 clicks in 193 click series recorded in the North Atlantic. The analysis of IPI could be done with reasonable reproducibility using a minimum of equipment: a tape recorder, filter, and oscilloscope. Criteria were developed to choose suitable clicks for analysis. In the click sample, 11% met the criteria for analysis, and were contained in 41 click series, of which 22 had a unique IPI. The IPIs in the 41 series ranged between 1.6 and 8.0 ms, and corresponded to a predicted size range of 7–22 m. This is consistent for the size range reported for the western North Atlantic.Key words: bioacoustics, sperm whale, Physeter catodon, size determination, click, interpulse interval
Seasonal Variation of Potential Nutrient Limitation to Chlorophyll Production in Southern Lake Huron
Authors: Lin C. Kwei , Schelske Claire L.
Published: November 2009

Potential nutrient limitation to chlorophyll production in surface waters of southern Lake Huron was assayed monthly from April to December 1975. Natural phytoplankton assemblage responses to nutrient enrichment were determined from chlorophyll production in laboratory incubations under seasonally varied light and temperature conditions. Experimental treatments included a complete treatment containing P, N, Si, EDTA, vitamins, and trace metals; treatments with deletions from the complete treatment; complete treatments with different P concentrations; and treatments with single nutrient additions. Effects were most pronounced during summer and fall when P, EDTA, FeEDTA, vitamins, and Si were added simultaneously. The intensity of the effect resulting from additions of phosphorus and other nutrients varied seasonally. Individual additions of EDTA, N, and Si had little effect as did deletion of N from the complete treatment. Addition of P alone resulted in limited growth. Deletion of phosphorus from the complete enrichment, however, reduced growth drastically during most experimental periods. In the complete treatment the minimum levels of P that caused significant chlorophyll production ranged from 1 to 3 μg L−1. Chelate (EDTA), chelated iron, and vitamins were important secondary limiting nutrients during the summer months. There was a small effect due to silica in July, September, and October, and no indication of deficiency in trace metals. Trace metals, when deleted, frequently produced greater chlorophyll than the complete treatment, but growth was sharply reduced by deletion of trace metals and EDTA combined. The results clearly demonstrate that large increases in chlorophyll production in southern Lake Huron require simultaneous additions of the primary limiting nutrient (P) and secondary limiting nutrients (EDTA, FeEDTA, and vitamins) which vary seasonally.Key words: chlorophyll, eutrophication, micronutrients, phosphorus, phytoplankton
Detecting Temperature Fine Structure and Mesoscale Frontal Regimes along Line P in the Northeastern Pacific Ocean
Authors: Thomson Richard E. , Kuwahara Liliane S. C.
Published: November 2009

Temperature observations obtained at 13 line P stations by Canadian weatherships for the period 1969–1977 show evidence for two quasi-permanent mesoscale frontal regimes west of Vancouver Island, British Columbia. Findings are based on vertically smoothed digitized STD profiles and normalized variances for temperature fine structure having vertical scales of a few tens of metres. A major frontal boundary crosses line P in the vicinity of 128°40′W longitude to depths of 700 m and in the vicinity of 130°40′W longitude between depths of 700 and 1300 m. Over certain depth ranges, location of the front varies seasonally, with a tendency for the front to be further offshore in winter than in summer. There is also some suggestion of a secondary, poorly defined frontal boundary in the region of 136–139°W longitude.Key words: ocean fronts, line P, northeast Pacific, temperature fine structure
Pup Production Following Harvest of Female Northern Fur Seals
Authors: York Anne E. , Hartley James R.
Published: November 2009

Female northern fur seals (Callorhinus ursinus) were harvested commercially from 1956 to 1968 and pelagic collections were taken for research purposes from 1958 to 1974. Early survival rates (birth to age 2) for males increased from an average of 0.32 before the harvest to 0.38 afterwards. Numbers of female pups whose births were precluded by the harvest are estimated for the years 1956–79; these account for about 70% of the difference between the numbers of pups actually born and the level of pup births before 1956. Estimates of the increased numbers of pups due to the increase in the early survival rates are presented for the years 1958–74.Key words: northern fur seal, population dynamics, female harvest, cohort analysis, St. Paul Island
Effectiveness of Fine Mesh Cylindrical Wedge-Wire Screens in Reducing Entrainment of Lake Michigan Ichthyoplankton
Authors: Zeitoun Ibrahim H. , Gulvas John A. , Roarabaugh Doyle B.
Published: November 2009

Samples of ichthyoplankton entrained through 2.0-mm and 9.5-mm-slot opening cylindrical wedge-wire screens and through an open pipe (control) were collected in June, July, and August 1979, 1067 m off the southeast shore of Lake Michigan at a depth of 10.7 m. Screens were designed for a flow rate of 1.9 m3 min−1 at 15.2 cm s−1 through slot velocity. Ambient composition and density of ichthyoplankton were determined by net tows. Rainbow smelt (Osmerus mordax), alewife (Alosa pseudoharengus), and yellow perch (Perca flavescens) larvae were common in both entrainment and tow collections. Eggs were found almost exclusively in entrainment collections. Ambient larval fish densities were about 11 times greater than those found in entrainment collections. Total entrainments through either screen and the open pipe were not statistically significant. Larval avoidance and, to a lesser extent, screen exclusion were responsible for the low entrainment. We estimated that about 90% of native fish larvae at the site avoided pumping.Key words: Lake Michigan, fish larvae, fish eggs, ichthyoplankton, entrainment, power plants, avoidance
Zooplankton and Potential Fish Production in Lake Ontario
Authors: Borgmann U. , Shear H. , Moore J.
Published: November 2009

We calculated the annual production of epilimnetic crustacean zooplankton in Lake Ontario from data on the abundance of each species and its eggs, and from predictions of egg development times. Bosmina longirostris is the most productive species at the nearshore stations whereas Diacyclops thomasi is the most productive offshore. Total crustacean zooplankton production is fairly uniform throughout the lake, both nearshore and offshore, with the possible exception of somewhat reduced production at the western end of the lake. Average total production was estimated at 15 g∙m−2∙yr−1. Using a recent estimate of particle-size-conversion efficiency in Lake Ontario, obtained from data on contaminant concentrations in aquatic biota, we predicted potential fish production in the lake for various sizes of fish. From published data on the commercial fish harvest from 1910 to 1930, a time period when commercial production was at a maximum, we estimate that the past commercial harvest for pelagic species may have been 20% or more of our predicted potential production.
Pacific Salmon (Oncorhynchus) Migrations: Orientation versus Random Movement
Authors: Quinn Thomas P. , Groot Cornelis
Published: November 2009

A computer simulation by Saila and Shappy (1963. J. Cons. Int. Explor. Mer 28: 153–166) indicated that the migrations of Pacific salmon (Oncorhynchus) from high seas feeding areas to the coastal vicinity of their natal stream may be accomplished with only slight homeward orientation. Five assumptions in this important paper are here reexamined to determine the validity of the original conclusion in light of current knowledge of Pacific salmon biology. It appears that assumptions concerning swimming speed, duration of migration, and return success were incorrect. These errors resulted in substantially underestimating the extent of salmon homeward orientation. Thus, contrary to the original conclusion, any hypothesis concerning the high seas migrations of salmon must explain the strong orientation of these fishes in the open ocean.
Statistical Inference in Life-Table Experiments: The Finite Rate of Increase
Authors: Rago Paul J. , Dorazio Robert M.
Published: November 2009

Life-table experiments are frequently used to examine the effects of food level, toxicants, and other experimental treatments on a population's finite rate of increase λ. Although methods for computing the variance of λ have been suggested, the sampling distribution of λ, which is needed for statistical inference, has not been described. We used Monte Carlo procedures to simulate sampling distributions of λ for a variety of assumptions regarding survivorship and fecundity schedules and initial cohort sizes. The distribution of λ can be bimodal when cohort size is small and when juvenile mortality is large. Under these circumstances the probability that none of the initial cohort members reproduces is high enough to produce a significant frequency of zero values for λ. Zero therefore becomes the lower mode of the distribution. Many commonly observed mortality schedules and commonly used cohort sizes yield distributions of λ that are skewed toward low values. Although the skewness and variance of distributions of λ decrease as cohort size increases, these distributions are asymptotically non-normal. Normal-based statistical procedures for comparing experimental estimates of λ may therefore be misleading. To compare estimates of λ obtained from life-table experiments, we recommend using a Monte Carlo approach to generate sampling distributions of λ and then comparing these distributions directly. We illustrate this procedure with life-table data from Daphnia pulex cohorts raised at different levels of pH. We also show that a Taylor series variance estimator yields confidence intervals for λ that approximate those obtained from simulations. This variance estimator is less conservative, and therefore more useful, than a previous estimator derived by Lenski and Service (1982. Ecology 63: 655–662).
META-STABLE BRANE CONFIGURATIONS BY HIGHER-ORDER POLYNOMIAL SUPERPOTENTIAL
Authors: AHN CHANGHYUN
Published: November 2009

We construct the type IIA nonsupersymmetric meta-stable brane configuration consisting of (2k+1) NS5-branes and D4-branes where the electric gauge theory superpotential has an order (2k+2) polynomial for the bifundamentals. We find a rich pattern of nonsupersymmetric meta-stable states as well as the supersymmetric stable ones. By adding the orientifold 4-plane to this brane configuration, we also describe the intersecting brane configuration of type IIA string theory corresponding to the meta-stable nonsupersymmetric vacua of corresponding gauge theory.
NEUTRAL HIGGS BOSON PAIR-PRODUCTION AND TRILINEAR SELF-COUPLINGS IN THE MSSM AT ILC AND CLIC ENERGIES
Authors: GUTIÉRREZ-RODRÍGUEZ A. , HERNÁNDEZ-RUÍZ M. A. , SAMPAYO O. A.
Published: November 2009

We study pair-production as well as the triple self-couplings of the neutral Higgs bosons of the Minimal Supersymmetric Standard Model (MSSM) at the future International Linear e+e-Collider (ILC) and Compact Linear Collider (CLIC). The analysis is based on the reactions [Formula: see text] with hi= h, H, A. We evaluate the total cross-section for both [Formula: see text] and calculate the total number of events considering the complete set of Feynman diagrams at tree-level. We vary the triple couplings κλhhh, κλHhh, κλhAA, κλHAA, κλhHHand κλHHHwithin the range κ = -1 and +2. The numerical computation is done for the energies expected at the ILC with a center-of-mass energy 500, 1000, 1600 GeV and a luminosity 1000 fb-1. The channels [Formula: see text] and [Formula: see text] are also discussed to a center-of-mass energy of 3 TeV and luminosities of 1000 fb-1and 5000 fb-1.
SPHERICALLY SYMMETRIC TRAPPING HORIZONS, THE MISNER–SHARP MASS AND BLACK HOLE EVAPORATION
Authors: NIELSEN ALEX B. , YEOM DONG-HAN
Published: November 2009

We discuss some of the issues relating to information loss and black hole thermodynamics in the light of recent work on local black hole horizons. Understood in terms of pure states evolving into mixed states, the possibility of information loss in black holes is closely related to the global causal structure of space–time, as is the existence of event horizons. However, black holes need not be defined by event horizons, and in fact we argue that in order to have a fully unitary evolution for black holes, they should be defined in terms of something else, such as a trapping horizon. The Misner–Sharp mass in spherical symmetry shows very simply how trapping horizons can give rise to black hole thermodynamics, Hawking radiation and singularities. We show how the Misner–Sharp mass can also be used to give insights into the process of collapse and evaporation of locally defined black holes.
CHIRAL ALGEBRAS FOR SUPERCONFORMAL INTERACTING BOSONS
Authors: GEPNER DORON
Published: November 2009

A sort of calculus is developed to find the chiral algebras of N = 2 superconformal interacting bosonic models. Many examples are discussed. It is shown that the algebras share a common structure, which we call almost Landau Ginzburg. For one or two generators, the number of relations is equal to the number of generators and they are algebraically independent.
ANALYTICAL CONSIDERATIONS ABOUT THE COSMOLOGICAL CONSTANT AND DARK ENERGY
Authors: ABREU EVERTON M. C. , DE ASSIS LEONARDO P. G. , DOS REIS CARLOS M. L.
Published: November 2009

The accelerated expansion of the universe has now been confirmed by several independent observations including those of high redshift type Ia supernovae, and the cosmic microwave background combined with the large scale structure of the universe. Another way of presenting this kinematic property of the universe is to postulate the existence of a new and exotic entity, with negative pressure, the dark energy (DE). In spite of observationally well established, no single theoretical model provides an entirely compelling framework within which cosmic acceleration or DE can be understood. At present all existing observational data are in agreement with the simplest possibility that the cosmological constant be a candidate for DE. This case is internally self-consistent and noncontradictory. The extreme smallness of the cosmological constant expressed in either Planck, or even atomic units means only that its origin is not related to strong, electromagnetic, and weak interactions. Although in this case DE reduces to only a single fundamental constant we still have no derivation from any underlying quantum field theory for its small value. From the principles of quantum cosmologies, for example, it is possible to obtain the reason for an inverse-square law for the cosmological constant with no conflict with observations. Despite the fact that this general expression is well known, in this work we introduce families of analytical solutions for the scale factor different from the current literature. The knowledge of the scale factor behavior might shed some light on these questions mentioned above since the entire evolution of a homogeneous isotropic universe is contained in the scale factor. We use different parameters for these solutions and with these parameters we establish a connection with the equation of state for different DE scenarios.
IMPROVED ARBITRARY l-STATE SOLUTIONS OF THE HULTHÉN POTENTIAL
Authors: QIANG WEN-CHAO , CHEN WEN LI , LI KAI , ZHANG HUA-PING
Published: November 2009

We developed a new and simple approximation scheme for centrifugal term. Using the new approximate formula for 1/r2 we derived approximately analytical solutions to the radial Schrödinger equation of the Hulthén potential with arbitrary l-states. Normalized analytical wave-functions are also obtained. Some energy eigenvalues are numerically calculated and compared with those obtained by C. S. Jia et al. and other methods such as the asymptotic iteration, the supersymmetry, the numerical integration methods and a Mathematica program, schroedinger, by W. Lucha and F. F. Schöberl.
Inhibition of transforming growth factor-β signaling induces left ventricular dilation and dysfunction in the pressure-overloaded heart
Authors: Lucas Jason A. , Zhang Yun , Li Peng , Gong Kaizheng , Miller Andrew P. , Hassan Erum , Hage Fadi , Xing Dongqi , Wells Bryan , Oparil Suzanne , Chen Yiu-Fai
Published: November 2009

This study utilized a transgenic mouse model that expresses an inducible dominant-negative mutation of the transforming growth factor (TGF)-β type II receptor (DnTGFβRII) to define the structural and functional responses of the left ventricle (LV) to pressure-overload stress in the absence of an intact TGF-β signaling cascade. DnTGFβRII and nontransgenic (NTG) control mice (male, 8–10 wk) were randomized to receive Zn2+ (25 mM ZnSO4 in drinking H2O to induce DnTGFβRII gene expression) or control tap H2O and then further randomized to undergo transverse aortic constriction (TAC) or sham surgery. At 7 days post-TAC, interstitial nonmyocyte proliferation (Ki67 staining) was greatly reduced in LV of DnTGFβRII+Zn2+ mice compared with the other TAC groups. At 28 and 120 days post-TAC, collagen deposition (picrosirius-red staining) in LV was attenuated in DnTGFβRII+Zn2+ mice compared with the other TAC groups. LV end systolic diameter and end systolic and end diastolic volumes were markedly increased, while ejection fraction and fractional shortening were significantly decreased in TAC-DnTGFβRII+Zn2+ mice compared with the other groups at 120 days post-TAC. These data indicate that interruption of TGF-β signaling attenuates pressure-overload-induced interstitial nonmyocyte proliferation and collagen deposition and promotes LV dilation and dysfunction in the pressure-overloaded heart, thus creating a novel model of dilated cardiomyopathy.
Development of an anatomically detailed MRI-derived rabbit ventricular model and assessment of its impact on simulations of electrophysiological function
Authors: Bishop Martin J. , Plank Gernot , Burton Rebecca A. B. , Schneider Jürgen E. , Gavaghan David J. , Grau Vicente , Kohl Peter
Published: November 2009

Recent advances in magnetic resonance (MR) imaging technology have unveiled a wealth of information regarding cardiac histoanatomical complexity. However, methods to faithfully translate this level of fine-scale structural detail into computational whole ventricular models are still in their infancy, and, thus, the relevance of this additional complexity for simulations of cardiac function has yet to be elucidated. Here, we describe the development of a highly detailed finite-element computational model (resolution: ∼125 μm) of rabbit ventricles constructed from high-resolution MR data (raw data resolution: 43 × 43 × 36 μm), including the processes of segmentation (using a combination of level-set approaches), identification of relevant anatomical features, mesh generation, and myocyte orientation representation (using a rule-based approach). Full access is provided to the completed model and MR data. Simulation results were compared with those from a simplified model built from the same images but excluding finer anatomical features (vessels/endocardial structures). Initial simulations showed that the presence of trabeculations can provide shortcut paths for excitation, causing regional differences in activation after pacing between models. Endocardial structures gave rise to small-scale virtual electrodes upon the application of external field stimulation, which appeared to protect parts of the endocardium in the complex model from strong polarizations, whereas intramural virtual electrodes caused by blood vessels and extracellular cleft spaces appeared to reduce polarization of the epicardium. Postshock, these differences resulted in the genesis of new excitation wavefronts that were not observed in more simplified models. Furthermore, global differences in the stimulus recovery rates of apex/base regions were observed, causing differences in the ensuing arrhythmogenic episodes. In conclusion, structurally simplified models are well suited for a large range of cardiac modeling applications. However, important differences are seen when behavior at microscales is relevant, particularly when examining the effects of external electrical stimulation on tissue electrophysiology and arrhythmia induction. This highlights the utility of histoanatomically detailed models for investigations of cardiac function, in particular for future patient-specific modeling.
A Recurrence Formula forDNumbers D2n(21n−)
Authors: Liu Guodong
Published: November 2009

we establish a recurrence formula forDnumbers . A generating function forDnumbers is also presented.
Star Formation Histories of Dwarf Galaxies from the Colour‐Magnitude Diagrams of Their Resolved Stellar Populations
Authors: Cignoni Michele , Tosi Monica
Published: November 2009

In this tutorial paper we summarize how the star formation (SF) history of a galactic region
can be derived from the colour‐magnitude diagram (CMD) of its resolved stars. The procedures to
build synthetic CMDs and to exploit them to derive the SF histories (SFHs) are described, as well
as the corresponding uncertainties. The SFHs of resolved dwarf galaxies of all morphological types,
obtained from the application of the synthetic CMD method, are reviewed and discussed. To summarize:
(1) only early‐type galaxies show evidence of long interruptions in the SF activity; late‐type dwarfs
present rather continuous, or gasping, SF regimes; (2) a few early‐type dwarfs have experienced only
one episode of SF activity concentrated at the earliest epochs, whilst many others show extended
or recurrent SF activity; (3) no galaxy experiencing now its first SF episode has been found yet; (4)
no frequent evidence of strong SF bursts is found; (5) there is no significant difference in the SFH
of dwarf irregulars and blue compact dwarfs, except for the current SF rates. Implications of these
results on the galaxy formation scenarios are briefly discussed.
Vascular Smooth Muscle Cell Apoptosis Induces Interleukin-1–Directed Inflammation
Authors: Clarke Murray C.H. , Talib Sara , Figg Nichola L. , Bennett Martin R.
Published: November 2009

Rationale
:

Atherosclerosis is characterized by lipid accumulation in the vessel wall, inflammation, and both macrophage and vascular smooth muscle cell (VSMC) apoptosis. However, whereas VSMC apoptosis in mice with established atherosclerotic plaques or hyperlipidemia increases serum levels of the proatherogenic cytokines monocyte chemotactic protein (MCP)-1, tumor necrosis factor α, and interleukin (IL)-6, the link between hyperlipidemia, apoptosis and inflammation, and the mechanisms by which apoptotic cells promote inflammation in atherosclerosis are unknown.

Objective
:

To determine whether hyperlipidemia affects apoptotic cell clearance, and identify the molecular pathways downstream of VSMC apoptosis that may promote inflammation.

Methods and Results
:

We find that human VSMCs are potent and efficient phagocytes of apoptotic human VSMCs, but phagocytosis is significantly reduced by oxidized low-density lipoprotein in vitro or hyperlipidemia in vivo. Necrotic human aortic VSMCs release IL-1α, which induces IL-6 and MCP-1 production from viable human VSMCs in vitro. In contrast, secondary necrotic VSMCs release both IL-1α and caspase-activated IL-1β, augmenting IL-6 and MCP-1 production. Conditionally inducing VSMC apoptosis in situ in hyperlipidemic SM22α-hDTR/ApoE
−/−
mice to levels seen in human plaques increases serum MCP-1, tumor necrosis factor α, and IL-6, which is prevented by blocking IL-1.

Conclusions
:

We conclude that VSMC necrosis releases IL-1α, whereas secondary necrosis of apoptotic VSMCs releases both IL-1α and β. IL-1 from necrotic VSMCs induces the surrounding viable VSMCs to produce proinflammatory cytokines. Thus, failed clearance of apoptotic VSMCs caused by hyperlipidemia in vivo may promote the increased serum cytokines and chronic inflammation associated with atherosclerosis.
Low Risk of Ipsilateral Stroke in Patients With Asymptomatic Carotid Stenosis on Best Medical Treatment
Authors: Marquardt Lars , Geraghty Olivia C. , Mehta Ziyah , Rothwell Peter M.
Published: November 2009

Background and Purpose—

The annual risk of ischemic stroke distal to ≥50% asymptomatic carotid stenoses was ≈2% to 3% in early cohort studies and subsequent randomized trials of endarterectomy. This risk might have fallen in recent years owing to improvements in medical treatment, but there are no published prognostic data from studies initiated within the last 10 years.

Methods—

In a population-based study of all patients with transient ischemic attack (TIA) or stroke in the Oxford Vascular Study, we studied the risk of TIA and stroke in patients with ≥50% contralateral asymptomatic carotid stenoses recruited consecutively from 2002 to 2009 and given intensive contemporary medical treatment.

Results—

Of 1153 consecutively imaged patients presenting with stroke or TIA, 101 (8.8%) had ≥50% asymptomatic carotid stenoses (mean age, 75 years; 39% women; 40% age ≥80 years). During 301 patient-years of follow-up (mean, 3 years), there were 6 ischemic events in the territory of an asymptomatic stenosis, 1 minor stroke (initially 50% to 69% stenosis), and 5 TIAs (2 initially 50% to 69% stenosis; 3 to 70% to 99% stenosis), 3 of which led to subsequent endarterectomy. The average annual event rates on medical treatment were 0.34% (95% CI, 0.01 to 1.87) for any ipsilateral ischemic stroke, 0% (95% CI, 0.00 to 0.99) for disabling ipsilateral stroke, and 1.78% (95% CI, 0.58 to 4.16) for ipsilateral TIA.

Conclusions—

In the first study of the prognosis of ≥50% asymptomatic carotid stenosis to be initiated in the last 10 years, the risk of stroke on intensive contemporary medical treatment was low. Larger studies are required to determine whether this apparent improvement in prognosis is generalizable.
Internal Jugular Vein Valve Incompetence Is Highly Prevalent in Transient Global Amnesia
Authors: Cejas Claudia , Cisneros Lucia Fernandez , Lagos Roberto , Zuk Carlos , Ameriso Sebastián F.
Published: November 2009

Background and Purpose—

Transient global amnesia (TGA) is the inability to retain new information and to recall past events during a period of minutes or hours. Its etiology is unclear, and flow disturbances in the mesial temporal lobes secondary to venous congestion have been proposed as a potential cause. Ultrasonographic evaluation of the internal jugular vein (IJV) has demonstrated valvular insufficiency in TGA. The prevalence of valvular insufficiency in the IJV in patients with TGA was assessed. Subjects without TGA of similar sex, age, and vascular risk factor profiles served as controls.

Methods—

A group of 142 patients with a clinical diagnosis of TGA within 7 days of the clinical event and 40 controls were prospectively evaluated. Venous Doppler examination of both IJVs was performed at baseline and after a manometer-controlled Valsalva maneuver. Valvular insufficiency was diagnosed when there was reflux for >0.8 seconds during the Valsalva maneuver.

Results—

Valve insufficiency was found in at least one jugular vein in 113 of 142 patients with TGA (79.5%) and in 10 of 40 controls (25.0%),
P
<0.01. The right side was affected more often than the left side,
P
<0.01, and 26.8% of the patients had bilateral incompetence.

Conclusions—

Patients with TGA have a high prevalence of IJV valve insufficiency. This finding may have pathophysiologic implications. Doppler evaluation of the IJVs with dynamic maneuvers may help in the evaluation of this usually benign condition.
Blood Pressure and White-Matter Disease Progression in a Biethnic Cohort
Authors: Gottesman Rebecca F. , Coresh Josef , Catellier Diane J. , Sharrett A. Richey , Rose Kathryn M. , Coker Laura H. , Shibata Dean K. , Knopman David S. , Jack Clifford R. , Mosley Thomas H.
Published: November 2009

Background and Purpose—

Blood pressure (BP) is a predictor of concurrent and subsequently measured white-matter hyperintensity (WMH), but longitudinal studies of WMH changes and data in black participants are lacking. We hypothesized that WMH progression would be (1) strongly related to BP in blacks and whites and (2) predicted more strongly by earlier (midlife) or cumulative BP measurements than by measures at older ages.

Methods—

Participants were 983 individuals (49% black) from the Atherosclerosis Risk in Communities (ARIC) Study who underwent cerebral magnetic resonance imaging in 1993–1995 and 2004–2006. Associations between BP (measured at each of 5 visits, in addition to a time-averaged cumulative BP) and progression of WMHs were analyzed and compared.

Results—

Cumulative systolic BP (SBP) was the strongest BP predictor of WMH progression in adjusted models. Higher cumulative SBP (by 20 mm Hg) was associated with greater progression of WMHs and was similar in blacks (2.5 cm
3
,
P
<0.0001) and whites (2.6 cm
3
,
P
<0.0001). Higher cumulative SBP (per 20 mm Hg) was also associated with being in the top quintile of WMH progression (adjusted odds ratio=2.0; 95% CI, 1.6 to 2.6). Earlier SBP measurements were stronger predictors of WMH progression than were later SBP measurements, but in blacks only.

Conclusions—

In this population-based cohort, cumulative SBP was a stronger predictor of WMH progression than SBP from individual visits, in both blacks and whites. Earlier BPs were stronger predictors than BPs measured at later time points in blacks only.
To Choose or to Avoid: Age Differences in Learning from Positive and Negative Feedback
Authors: Eppinger Ben , Kray Jutta
Published: November 2009

In this study, we investigated whether older adults learn more from bad than good choices than younger adults and whether this is reflected in the error-related negativity (ERN). We applied a feedback-based learning task with two learning conditions. In the positive learning condition, participants could learn to choose responses that lead to monetary gains, whereas in the negative learning condition, they could learn to avoid responses that lead to monetary losses. To test the stability of learning preferences, the task involved a reversal phase in which stimulus–response assignments were inverted. Negative learners were defined as individuals that performed better in the negative than in the positive learning condition (and vice versa for positive learners). The behavioral data showed strong individual differences in learning from positive and negative outcomes that persisted throughout the reversal phase and were more pronounced for older than younger adults. Older negative learners showed a stronger tendency to avoid negative outcomes than younger negative learners. However, contrary to younger adults, this negative learning bias was not associated with a larger ERN, suggesting that avoidance learning in older negative learners might be decoupled from error processing. Furthermore, older adults showed learning impairments compared to younger adults. The ERP analyses suggest that these impairments reflect deficits in the ability to build up relational representations of ambiguous outcomes.
Dissociable Neural Substrates for Agentic versus Conceptual Representations of Self
Authors: Powell Lindsey J. , Macrae C. Neil , Cloutier Jasmin , Metcalfe Janet , Mitchell Jason P.
Published: November 2009

Although humans generally experience a coherent sense of selfhood, we can nevertheless articulate different aspects of self. Recent research has demonstrated that one such aspect of self—conceptual knowledge of one's own personality traits—is subserved by ventromedial prefrontal cortex (vMPFC). Here, we examined whether an alternative aspect of “self”—being an agent who acts to achieve one's own goals—relies on cognitive processes that overlap with or diverge from conceptual operationalizations of selfhood. While undergoing fMRI, participants completed tasks of both conceptual self-reference, in which they judged their own or another person's personality traits, and agentic self-reference, in which they freely chose an object or watched passively as one was chosen. The agentic task failed to modulate vMPFC, despite producing the same memory enhancement frequently observed during conceptual self-referential processing (the “self-reference” effect). Instead, agentic self-reference was associated with activation of the intraparietal sulcus (IPS), a region previously implicated in planning and executing actions. Experiment 2 further demonstrated that IPS activity correlated with later memory performance for the agentic, but not conceptual, task. These results support views of the “self” as a collection of distinct mental operations distributed throughout the brain, rather than a unitary cognitive system.
Neural Activity in the Hippocampus and Perirhinal Cortex during Encoding Is Associated with the Durability of Episodic Memory
Authors: Carr Valerie A. , Viskontas Indre V. , Engel Stephen A. , Knowlton Barbara J.
Published: November 2009

Studies examining medial temporal lobe (MTL) involvement in memory formation typically assess memory performance after a single, short delay. Thus, the relationship between MTL encoding activity and memory durability over time remains poorly characterized. To explore this relationship, we scanned participants using high-resolution functional imaging of the MTL as they encoded object pairs; using the remember/know paradigm, we then assessed memory performance for studied items both 10 min and 1 week later. Encoding trials were classified as either subsequently recollected across both delays, transiently recollected (i.e., recollected at 10 min but not after 1 week), consistently familiar, or consistently forgotten. Activity in perirhinal cortex (PRC) and a hippocampal subfield comprising the dentate gyrus and CA fields 2 and 3 reflected successful encoding only when items were recollected consistently across both delays. Furthermore, in PRC, encoding activity for items that later were consistently recollected was significantly greater than that for transiently recollected and consistently familiar items. Parahippocampal cortex, in contrast, showed a subsequent memory effect during encoding of items that were recollected after 10 min, regardless of whether they also were recollected after 1 week. These data suggest that MTL subfields contribute uniquely to the formation of memories that endure over time, and highlight a role for PRC in supporting subsequent durable episodic recollection.
Neural Dissociations between Action Verb Understanding and Motor Imagery
Authors: Willems Roel M. , Toni Ivan , Hagoort Peter , Casasanto Daniel
Published: November 2009

According to embodied theories of language, people understand a verb like throw, at least in part, by mentally simulating throwing. This implicit simulation is often assumed to be similar or identical to motor imagery. Here we used fMRI to test whether implicit simulations of actions during language understanding involve the same cortical motor regions as explicit motor imagery. Healthy participants were presented with verbs related to hand actions (e.g., to throw) and nonmanual actions (e.g., to kneel). They either read these verbs (lexical decision task) or actively imagined performing the actions named by the verbs (imagery task). Primary motor cortex showed effector-specific activation during imagery, but not during lexical decision. Parts of premotor cortex distinguished manual from nonmanual actions during both lexical decision and imagery, but there was no overlap or correlation between regions activated during the two tasks. These dissociations suggest that implicit simulation and explicit imagery cued by action verbs may involve different types of motor representations and that the construct of “mental simulation” should be distinguished from “mental imagery” in embodied theories of language.
Modulation of BOLD Response in Motion-sensitive Lateral Temporal Cortex by Real and Fictive Motion Sentences
Authors: Saygin Ayse Pinar , McCullough Stephen , Alac Morana , Emmorey Karen
Published: November 2009

Can linguistic semantics affect neural processing in feature-specific visual regions? Specifically, when we hear a sentence describing a situation that includes motion, do we engage neural processes that are part of the visual perception of motion? How about if a motion verb was used figuratively, not literally? We used fMRI to investigate whether semantic content can “penetrate” and modulate neural populations that are selective to specific visual properties during natural language comprehension. Participants were presented audiovisually with three kinds of sentences: motion sentences (“The wild horse crossed the barren field.”), static sentences, (“The black horse stood in the barren field.”), and fictive motion sentences (“The hiking trail crossed the barren field.”). Motion-sensitive visual areas (MT+) were localized individually in each participant as well as face-selective visual regions (fusiform face area; FFA). MT+ was activated significantly more for motion sentences than the other sentence types. Fictive motion sentences also activated MT+ more than the static sentences. Importantly, no modulation of neural responses was found in FFA. Our findings suggest that the neural substrates of linguistic semantics include early visual areas specifically related to the represented semantics and that figurative uses of motion verbs also engage these neural systems, but to a lesser extent. These data are consistent with a view of language comprehension as an embodied process, with neural substrates as far reaching as early sensory brain areas that are specifically related to the represented semantics.