bluuebunny/crossref_metadata_2025 huggingface dataset:
Abundance Gradients and Chemical Evolution of Spiral Galaxies
Authors: Marcon-Uchida Monica M. , Matteucci Francesca , Costa Roberto D. D.
Published: March 2010

The distribution of chemical abundances and their variation in space and time are important tools to understand the chemical evolution of disks in spiral galaxies. In this work we present an one infall chemical evolution model for the Galactic disk based on an updated version of the Trieste group model. We adopted a pre enriched gas (to take into account the effect of the halo evolution), an inside-out scenario for the formation of the disk and a threshold in the surface gas density to regulate the star formation rate. The observational constraints for the solar neighbourhood were well reproduced and the spatial and time evolution of the radial abundance gradient were studied. We also used this model to reproduce the chemical evolution of some nearby spiral galaxies. The model was scaled to the disk properties of each galaxy and its dependence with the star formation efficiency and the time scale for the infalling gas into the disk were explored. Using this modified model we were able to reproduce the observed constraints available in the literature for this galaxies. The similarities and the differences between the chemical evolution of these objects and teh Milky Way are discussed to provide a basis to the understanding of the chemical evolution of disks.
Spitzer finds cosmic neon's and sulfur's sweet spot: part III, NGC 6822
Authors: Rubin R. H. , McNabb I. A. , Simpson J. P. , Dufour R. J. , Pauldrach A. W. A. , Colgan S. W. J. , Craven T. W. , Gitterman E. D. , Lo C. C.
Published: March 2010

We observed several H ii regions in the dwarf irregular galaxy NGC 6822 using the infrared spectrograph on the Spitzer Space Telescope. Our aim is twofold: first, to examine the neon to sulfur abundance ratio in order to determine how much it may vary and whether or not, it is fairly ‘universal’; second, to discriminate and test the predicted ionizing spectral energy distribution between various stellar atmosphere models by comparing with our derivation of the ratio of fractional ionizations involving neon and sulfur. This work extends our previous similar studies of H ii regions in M83 and M33 to lower metallicities.
The Galactic Thick Disk: An Observational Perspective
Authors: Reddy Bacham E.
Published: March 2010

In this review, we present a brief description of observational efforts to understand the Galactic thick disk and its relation to the other Galactic components. This review primarily focused on elemental abundance patterns of the thick disk population to understand the process or processes that were responsible for its existence and evolution. Kinematic and chemical properties of disk stars establish that the thick disk is a distinct component in the Milky Way, and its chemical enrichment and star formation histories hold clues to the bigger picture of understanding the Galaxy formation.
The Galactic thin and thick disks in the context of galaxy formation
Authors: Bensby Thomas , Feltzing Sofia
Published: March 2010

We have obtained high-resolution spectra and carried out a detailed elemental abundance analysis for a new sample of 899 F and G dwarf stars in the Solar neighbourhood. The results allow us to, in a multi-dimensional space consisting of stellar ages, detailed elemental abundances, and full kinematic information for the stars, study and trace their respective origins. Here we briefly address selection criteria and discuss how to define a thick disc star. The results are discussed in the context of galaxy formation.
Chemical similarities between the Galactic bulge and local thick disk red giant stars: analysis from optical data
Authors: Alves-Brito Alan , Meléndez Jorge , Asplund Martin
Published: March 2010

The Galactic structure and composition remain as one of the greatest open problems in modern astrophysics. We show here that there are chemical similarities between the Galactic bulge and local thick disk red giant stars. This finding puts strong constraints on the IMF, SFR and chemical enrichment timescale of the bulge and thick disk. Our results are based upon a detailed elemental abundance analysis of 80 high S/N and high resolution optical spectra of giant stars, in the range −1.5 < [Fe/H] < +0.5.
Atmospheric Parameters and Chemical Abundances for Herbig Ae stars
Authors: Castilho Bruno V. , Daflon Simone , Sartori Marília J. , Przybilla Norbert
Published: March 2010

In this work, we present temperature, surface gravity, metallicity, microturbulence and element abundances, determined from a detailed spectroscopic analysis for a sample of 9 Herbig Ae stars, based on high resolution, high S/N spectra.
On The Physical Existence of The Zeta Reticuli Moving Group: A Chemical Composition Analysis
Authors: Ferreira Letícia D. , de Mello Gustavo F. Porto , da Silva Licio
Published: March 2010

We report the spectroscopic analysis of six kinematical members of the Zeta Reticuli Moving Group, one of them for the first time. We confirm the existence of the Group by establishing a common abundance pattern for four kinematical members. High resolution spectra yielded abundances of Si, Ca, Fe, Ni and Ba, and others. Effective temperatures were derived from the excitation & ionization equilibria of Fe lines of four stars. For these, and the remaining two members, temperatures were derived from colors and the fitting of theoretical spectra to the Hα line, and ages and masses were estimated from theoretical HR diagrams. We suggest that the Group is physical being metal-poor and ~6 Gyr old.
Chemical Fingerprinting and Chemical Analysis of Galactic Halo Substructure
Authors: Majewski Steven R. , Chou Mei-Yin , Cunha Katia , Smith Verne V. , Patterson Richard J. , Martínez-Delgado David
Published: March 2010

We present high-resolution spectroscopic measurements of the abundances of the α-like element titanium (Ti) and s-process elements yttrium (Y) and lanthanum (La) for M giant candidates of (a) the Sagittarius (Sgr) dwarf spheroidal + tidal tail system, (b) the Triangulum-Andromeda (TriAnd) Star Cloud, and (c) the Galactic Anticenter Stellar Structure (GASS, or Monoceros Stream). All three systems show abundance patterns unlike the Milky Way but typical of dwarf galaxies. The Sgr system abundance patterns resemble those of the Large Magellanic Cloud. GASS/Mon chemically resembles Sgr but is distinct from TriAnd, a result that does not support previous suggestions that TriAnd is a piece of the Monoceros Stream.
FEROS Abundance Analysis of 21 Bulgelike SMR Stars
Authors: Trevisan Marina , Barbuy Beatriz , Grenon M. , Gustafsson B. , Pompéia L.
Published: March 2010

We analyze a sample of 21 super-metal-rich (SMR) stars, using high-resolution échelle spectra obtained with the Fiber-fed Extended Range Optical Spectrograph at the 1.5m ESO telescope. The metallicities are in the range 0.07 ≤ [Fe/H] ≤ 0.45, 3 of them in common with Pompéia et al. (2009). Geneva photometry, astrometric data from Hipparcos, and radial velocities from CORAVEL are available for these stars. The peculiar kinematics suggests the thin disk close to the bulge as the probable birthplace of these stars (Grenon 1999). From Hipparcos data, it appears that the turnoff of this population indicates an age of 10-11 Gyr (Grenon 1999). Detailed analysis of the sample stars is carried out, and atmospheric parameters are derived from spectroscopic and photometric determinations. Oxygen abundances of these stars are derived, and [O/Fe] overabundances up to +0.35 are found.
Unprecedented accurate abundances: signatures of other Earths?
Authors: Meléndez Jorge , Asplund Martin , Gustafsson Bengt , Yong David , Ramírez Iván
Published: March 2010

For more than 140 years the chemical composition of our Sun has been considered typical of solar-type stars. Our highly differential elemental abundance analysis of unprecedented accuracy (~0.01 dex) of the Sun relative to solar twins, shows that the Sun has a peculiar chemical composition with a ≈20% depletion of refractory elements relative to the volatile elements in comparison with solar twins. The abundance differences correlate strongly with the condensation temperatures of the elements. A similar study of solar analogs from planet surveys shows that this peculiarity also holds in comparisons with solar analogs known to have close-in giant planets while the majority of solar analogs without detected giant planets show the solar abundance pattern. The peculiarities in the solar chemical composition can be explained as signatures of the formation of terrestrial planets like our own Earth.
Evolution of the abundance of biomolecules in the interstellar medium at the gas phase
Authors: Penteado Eduardo M. , Rocha-Pinto Helio J.
Published: March 2010

Interstellar clouds are the sites where many molecules believed important for the early life are produced. The collapse of such clouds may give birth to stars hosting planetary systems. During the formation of such systems, molecules formed in the molecular cloud, aggregated into grains, can be incorporated in protoplanets, influencing the chemical evolution of the environment, probably affecting the chances for appearance of life on rocky planets located at the stellar habitable zones. Moreover, small bodies, like comets, can carry some of these molecules to inner planets of their systems. Using astrochemical equations, we describe the evolution of the abundance of such molecules at the gas phase from several initial interstellar compositions. These varying initial chemical compositions consider the change of the elemental abundances predicted by a self-consistent model of the chemical evolution of the Galaxy. A system of first order differential equations that describes the abundances of each molecule is solved numerically. This poster describes an innovative attempt to link the astrochemistry equations with the Galactic chemical evolution.
Correlation between the interaction of the vinculin tail domain with lipid membranes, its phosphorylation and cell mechanical behaviour
Authors: Goldmann Wolfgang H.
Published: March 2010

Cell adhesion and cell–cell contacts are a pre‐requisite for proper metabolism, protein synthesis and cell survival. Integrins are the transmembrane receptors that link the extracellular matrix via the FAC (focal adhesion complex) with the cytoskeleton. Vinculin is a pivotal FAC protein that has not only been implicated in regulating FAC formation and transmitting mechanical forces, but also in associating with membranous lipids in biological systems.
Another decade of advances in research on primary cilia, porosomes and neosis: Some passing thoughts at 70
Authors: Wheatley Denys N.
Published: March 2010

This editorial contains some of my reflections on a career spanning almost 50 years in biomedical research at the cellular level and over 12 years as Editor‐in‐Chief of Cell Biology International, at the time of my 70th birthday. It is gratifying that I have been involved in some of the more important organelles and processes that have come to the forefront of cell research today, and I have chosen just three examples to illustrate this point.
Effect of Destination Image on Attendance at Team Sporting Events
Authors: Mohan Leon J.
Published: March 2010

This study examines the relationship between destination image and attendance at professional hockey games. Thirteen destination image attributes were selected to measure the influence of destination image on the decision to attend road games of the Carolina Hurricanes. The study was conducted at the RBC Center in Raleigh, North Carolina, during a weekday home game and a weekend home game. Fans of differing levels of team identification were surveyed. The different levels of team identification ranged from season ticket holders to mini plan purchasers to game day purchasers. The results of the study indicated that destination image is a predictor of attendance at road games. Attributes, in particular, that were stronger influences on destination image included weather, cost, safety and hospitality. There were also no differences between weekday attendees and weekend attendees. However, fans who were season ticket holders or game day purchasers were influenced by destination image when deciding to travel to road games whereas mini plan purchasers were not.
Modeling the Kelvin polarization force actuation of micro- and nanomechanical systems
Authors: Schmid Silvan , Hierold Christofer , Boisen Anja
Published: March 2010

Polarization forces have become of high interest in micro- and nanomechanical systems. In this paper, an analytical model for a transduction scheme based on the Kelvin polarization force is presented. A dielectric beam is actuated by placing it over the gap of two coplanar electrodes. Finite element method simulations are used to characterize the scheme and to evaluate a field correction factor, which results from simplifying the form of the electric field. The model has been shown to be valid for dielectrics with different permittivities. The presented model facilitates the design of microresonators and nanoresonators with dielectric actuation, which offers a great freedom in the choice of structural material.
Thin film dielectric microstrip kinetic inductance detectors
Authors: Mazin Benjamin A. , Sank Daniel , McHugh Sean , Lucero Erik A. , Merrill Andrew , Gao Jiansong , Pappas David , Moore David , Zmuidzinas Jonas
Published: March 2010

Microwave kinetic inductance detectors, or MKIDs, are a type of low temperature detector that exhibit intrinsic frequency domain multiplexing at microwave frequencies. We present the first theory and measurements on a MKID based on a microstrip transmission line resonator. A complete characterization of the dielectric loss and noise properties of these resonators is performed, and agrees well with the derived theory. A competitive noise equivalent power of 5×10−17 W Hz−1/2 at 10 Hz has been demonstrated. The resonators exhibit the highest quality factors known in a microstrip resonator with a deposited thin film dielectric.
Resonant tunneling of electrons in quantum wires (Review)
Authors: Krive I. V. , Palevski A. , Shekhter R. I. , Jonson M.
Published: March 2010

We consider resonant electron tunneling in various nanostructures, including single-wall carbon nanotubes, molecular transistors, and quantum wires, formed in two-dimensional electron gas. The review starts with a textbook description of resonant tunneling of noninteracting electrons through a double-barrier structure. The effects of electron–electron interaction in sequential and resonant electron tunneling are studied by using the Luttinger liquid model of electron transport in quantum wires. The experimental aspects of the problem (fabrication of quantum wires and transport measurements) are also considered. The influence of vibrational and electromechanical effects on resonant electron tunneling in molecular transistors is discussed.
Zintl phase Yb1−xCaxCd2Sb2 with tunable thermoelectric properties induced by cation substitution
Authors: Cao Qi-Gao , Zhang Hui , Tang Mei-Bo , Chen Hao-Hong , Yang Xin-Xin , Grin Yuri , Zhao Jing-Tai
Published: March 2010

It has been shown previously that the thermoelectric properties of the Zintl phase compound YbCd2Sb2 can be finely tuned via Zn substitution at the Cd-site in the anionic (Cd2Sb2)2− framework. Here we report the results of the investigation of isoelectronic substitution of Yb by Ca. The p-type Yb1−xCaxCd2Sb2 (0.2≤x≤0.8) samples have been synthesized via a solid-state reaction followed by suitable cooling, annealing, grinding, and spark plasma sintering densification processes. In samples with x=0.2, 0.4, 0.5, 0.6, 0.8, the electrical conductivity, Seebeck coefficient, and thermal conductivity measurements have been carried out in the temperature range from 300 to 650 K. It is found that the Ca substitution effectively lowers the thermal conductivity for all samples at high temperature, while it significantly increases the Seebeck coefficient. As a result, the dimensionless figure of merit ZT of 0.96 has been attained at 650 K for samples with x=0.4, while the value is 0.78 for the unsubstituted YbCd2Sb2
Structural understanding of the spectral characteristics of SnO2:Eu:Y2O3, using extended x-ray absorption fine structure
Authors: Lahiri Debdutta , Ningthoujam R. S. , Bhattacharyya Dibyendu , Sharma Surinder M.
Published: March 2010

SnO 2 : Eu is a well-known luminescent material, emitting red and orange lines. The intensity ratio of red to orange emission, being sensitive to the deviation of Eu3+ ions from symmetric location, finds wide application as sensor. The luminescence intensity of such lanthanide-doped sensors is generally optimized by high temperature annealing. However, for the present system (SnO2:Eu) it had been found that the red emission suddenly disappears while annealing beyond 900 °C, which can however be recovered by dispersing the system in a secondary host matrix of Y2O3. Understanding the mechanism of this recovery has important implication for designing of phosphor. In this work, we structurally explain this spectral evolution, by employing x-ray absorption fine structure technique. The initial disappearance of the red line is realized to be due to the formation of Eu2Sn2O7 and the recovery, to the intercalation of the Eu3+ ions from the SnO2 surface into Y2O3. Oxygen vacancy in Y2O3 creates the asymmetric environment required for red line emission. The design implications of these findings are discussed.
Origin of anomalous hysteresis loops induced by femtosecond laser pulses in GdFeCo amorphous films
Authors: Xu Chudong , Chen Zhifeng , Chen Daxin , Zhou Shiming , Lai Tianshu
Published: March 2010

A controllable pump-pulse-number magneto-optical Kerr technique combined with an initializing field scanning approach is developed to eliminate and identify memory and accumulation effects, respectively, from external field history and multiple pulse excitations. A series of anomalous loops of GdFeCo films are measured for different amount of pump pulses using this technique, revealing that serious memory and accumulation effects exist in continuous-pulse-pumped anomalous hysteresis loops which show illusory information of hot coercivity and degree of magnetization reversal. Single-pulse-induced anomalous loop reveals that the hot coercivity shown by continuous-pulse-pumped anomalous loops is not the minimum external field that drives real magneto-optical recording.
Excitation energy transfer from a fluorophore to single-walled carbon nanotubes
Authors: Swathi R. S. , Sebastian K. L.
Published: March 2010

We study the process of electronic excitation energy transfer from a fluorophore to the electronic energy levels of a single-walled carbon nanotube. The matrix element for the energy transfer involves the Coulombic interaction between the transition densities on the donor and the acceptor. In the Förster approach, this is approximated as the interaction between the corresponding transition dipoles. For energy transfer from a dye to a nanotube, one can use the dipole approximation for the dye, but not for the nanotube. We have therefore calculated the rate using an approach that avoids the dipole approximation for the nanotube. We find that for the metallic nanotubes, the rate has an exponential dependence if the energy that is to be transferred, ℏΩ is less than a threshold and a d−5 dependence otherwise. The threshold is the minimum energy required for a transition other than the ki,⊥=0 and l=0 transition. Our numerical evaluation of the rate of energy transfer from the dye pyrene to a (5,5) carbon nanotube, which is metallic leads to a distance of ∼165 Å up to which energy transfer is appreciable. For the case of transfer to semiconducting carbon nanotubes, apart from the process of transfer to the electronic energy levels within the one electron picture, we also consider the possibility of energy transfer to the lowest possible excitonic state. Transfer to semiconducting carbon nanotubes is possible only if ℏΩ≥ϵg−ϵb. The long range behavior of the rate of transfer has been found to have a d−5 dependence if ℏΩ≥ϵg. But, when the emission energy of the fluorophore is in the range ϵg>ℏΩ≥ϵg−ϵb, the rate has an exponential dependence on the distance. For the case of transfer from pyrene to the semiconducting (6,4) carbon nanotube, energy transfer is found to be appreciable up to a distance of ∼175 Å.
Giant conductance anisotropy in magnetically coupled Ferromagnet-Superconductor-Ferromagnet structures
Authors: Belkin A. , Novosad V. , Iavarone M. , Divan R. , Hiller J. , Proslier T. , Pearson J. E. , Karapetrov G.
Published: March 2010

We demonstrate the evolution of the anisotropic conductivity in the superconductor that is magnetically coupled with two adjacent ferromagnetic layers. Stripe magnetic domain structure in the ferromagnetic layers results in directional superconducting order parameter in the superconducting layer. The conductance anisotropy strongly depends on the period of the magnetic domains and the strength of the local magnetization. The anisotropic conductivity of up to three orders of magnitude can be achieved with spatial critical temperature modulation of 5% of Tc. The effect could be exploited in low temperature nonvolatile logic and storage elements.
Communications: Polarity fluctuations of the protic ionic liquid ethylammonium nitrate in the terahertz regime
Authors: Krüger Matthias , Bründermann Erik , Funkner Stefan , Weingärtner Hermann , Havenith Martina
Published: March 2010

We have measured the complex dielectric function of the protic ionic liquid ethylammonium nitrate in the frequency range between 0.15 and 1.8 THz with a terahertz time domain spectrometer. The experiments reveal a terahertz mode which can be described as a damped harmonic oscillator with a central frequency of 1.3 THz. The terahertz mode is assigned to an intermolecular vibration, presumably associated with hydrogen-bond dynamics. The data are combined with microwave data to represent the dielectric spectrum from quasistatic conditions up to 1.8 THz.
Temperature dependence of intermediate-range orders in the viscosity-temperature relationship of supercooled liquids and glasses
Authors: Kobayashi Hiroshi , Takahashi Haruyuki
Published: March 2010

The viscosity-temperature relationship obtained by us for several glasses over a wide temperature range was analyzed by extending the Adam–Gibbs theory to the range below the glass transition temperature (Tg). The entropy change of the intermediate-range orders (IROs) is discussed on the basis of the theory developed by Prigogine. It is estimated that the time dependence of the vibrational entropy of a glass shows a constant decrease with a smallest change, while that of its configurational entropy is 0, keeping the constant fictive temperature and the isostructural state. The result predicts the decrease of the volume of a glass at the constant time-rate through spontaneous aging at the constant temperature. We also show that the glass transition is a phase transition from an equilibrium Vogel–Fulcher–Tamman state to a nonequilibrium and (meta-)stable Arrhenius state through fluctuations at Tg, and a microscopic feature of the glass transition is the self-organization of the IROs. These findings are extremely useful in analyzing glass and nanomaterial productions because the size of the IROs in the glass state is a few nanometers.
Temperature induced in-plane/out-of-plane magnetization transition in ferromagnetic Ga0.93Mn0.07As0.94P0.06/(100)GaAs thin films
Authors: Cubukcu M. , von Bardeleben H. J. , Cantin J. L. , Lemaître A.
Published: March 2010

Phosphorous alloying in the y=0.06 range allows to engineer ferromagnetic Ga1−xMnxAs1−yPy/(100)GaAs thin films with standard x=0.07 Mn doping in which the easy axes of magnetization can be changed from in-plane to out-of-plane by a small (10 K) temperature rise. Ferromagnetic resonance investigations show the reorientation to be induced by the different temperature dependence of the cubic and uniaxial anisotropy constants.
Experimental evidence for orientation property of Pb(Zr0.35Ti0.65)O3 by manipulating polar axis angle using CaF2 substrate
Authors: Utsugi Satoru , Fujisawa Takashi , Ehara Yoshitaka , Yamada Tomoaki , Matsushima Masaaki , Morioka Hitoshi , Funakubo Hiroshi
Published: March 2010

Perfectly oriented (001), (101), and (111) Pb(Zr0.35Ti0.65)O3 (PZT) films were grown on identical (111)CaF2 substrates by metal-organic chemical vapor deposition. These films exclude domains parallel to the surface; therefore, all domains are actively switchable under the electric field between top and bottom electrodes. Saturation polarization values, Psat(001), Psat(101), and Psat(111), for these PZT films were 75, 50, and 43 μC/cm2, respectively. This orientation dependency was in a good agreement with the theoretical relationship for a tetragonal PZT single crystal, where Psat(001)=Psat(101)/2=Psat(111)/3.
Strain relaxation in epitaxial (Pb,Sr)TiO3 thin films on NdGaO3 substrates
Authors: Lin Y. , Dai C. , Li Y. R. , Chen X. , Chen C. L. , Bhalla A. , Jia Q. X.
Published: March 2010

Strain relaxation behavior of (Pb,Sr)TiO3 thin films on (110) NdGaO3 substrates fabricated under different conditions have been investigated using high resolution x-ray diffraction. Dislocation densities and interfacial strain distribution have been systematically studied with samples in different postdeposition cooling rates. Strain relaxation and dislocation evolution are found to be dependent upon the cooling process. The relationship of dielectric properties and the strain and dislocations of the films were discussed.
Two millennia of North Atlantic seasonality and implications for Norse colonies
Authors: Patterson William P. , Dietrich Kristin A. , Holmden Chris , Andrews John T.
Published: March 2010

δ
18
O values of mollusks recovered from near-shore marine cores in northwest Iceland quantify significant variation in seasonal temperature over the period from ∼360 B.C. to ∼A.D. 1660. Twenty-six aragonitic bivalve specimens were selected to represent intervals of climatic interest by using core sedimentological characteristics. Carbonate powder was sequentially micromilled from shell surfaces concordant with growth banding and analyzed for stable oxygen (
δ
18
O) and carbon (
δ
13
C) isotope values. Because
δ
18
O values record subseasonal temperature variation over the lifetime of the bivalves, these data provide the first 2,000-year secular record of North Atlantic seasonality from
ca.
360 cal yr B.C. to cal yr A.D. 1660. Notable cold periods (360 B.C. to 240 B.C.; A.D. 410; and A.D. 1380 to 1420) and warm periods (230 B.C. to A.D. 140 and A.D. 640 to 760) are resolved in terms of contrast between summer and winter temperatures and seasonal temperature variability. Literature from the Viking Age (
ca.
790 to 1070) during the establishment of Norse colonies (and later) in Iceland and Greenland permits comparisons between the
δ
18
O temperature record and historical records, thereby demonstrating the impact of seasonal climatic extremes on the establishment, development, and, in some cases, collapse of societies in the North Atlantic.
Uniformity detector retinal ganglion cells fire complex spikes and receive only light-evoked inhibition
Authors: Sivyer Benjamin , Taylor W. Rowland , Vaney David I.
Published: March 2010

Retinal ganglion cells convey information by increasing their firing in response to an optimal visual stimulus or “trigger feature.” However, one class of ganglion cell responds to changes in the visual scene by decreasing its firing. These cells, termed uniformity detectors in the rabbit retina, are encountered only rarely and the synaptic mechanisms underlying their unusual responses have not been investigated. In this study, patch-clamp recordings of uniformity detectors show that the action potentials underlying the maintained firing arise within “complex spikes.” Both ON and OFF visual stimuli elicit only inhibitory synaptic input, the immediate effect of which is to suppress the maintained firing. However, this inhibition also alters the properties of the “renascent” spiking by increasing the amplitude of the spikes within each burst, suggesting that the effect may increase the efficacy of spike propagation and transmission.
Visualization of JNK activity dynamics with a genetically encoded fluorescent biosensor
Authors: Fosbrink Matthew , Aye-Han Nwe-Nwe , Cheong Raymond , Levchenko Andre , Zhang Jin
Published: March 2010

The signaling pathway mediated by JNK transduces different types of signals, such as stress stimuli and cytokines, into functional responses that mediate apoptosis, as well as proliferation, differentiation, and inflammation. To better characterize the dynamic information flow and signal processing of this pathway in the cellular context, a genetically encoded, fluorescent protein-based biosensor was engineered to detect endogenous JNK activity. This biosensor, named JNKAR1 (for JNK activity reporter), specifically detects stress- (ribotoxic and osmotic) and cytokine- (TNF-α) induced JNK activity in living cells with a 15 to 30% increase in the yellow-to-cyan emission ratio because of a phosphorylation-dependent increase in FRET between two fluorescent proteins. JNK activity was detected not only in the cytoplasm, but also in the nucleus, mitochondria, and plasma membrane with similar kinetics after induction of ribotoxic stress by anisomycin, suggesting relatively rapid signal propagation to the nuclear, mitochondrial, and plasma membrane compartments. Furthermore, quantitative single-cell analysis revealed that anisomycin-induced JNK activity exhibited ultrasensitivity, sustainability, and bimodality, features that are consistent with behaviors of bistable systems. The development of JNKAR1, therefore, laid a foundation for evaluating the signaling properties and behaviors of the JNK cascade in single living cells.
Ballistic tongue projection in chameleons maintains high performance at low temperature
Authors: Anderson Christopher V. , Deban Stephen M.
Published: March 2010

Environmental temperature impacts the physical activity and ecology of ectothermic animals through its effects on muscle contractile physiology. Sprinting, swimming, and jumping performance of ectotherms decreases by at least 33% over a 10 °C drop, accompanied by a similar decline in muscle power. We propose that ballistic movements that are powered by recoil of elastic tissues are less thermally dependent than movements that rely on direct muscular power. We found that an elastically powered movement, ballistic tongue projection in chameleons, maintains high performance over a 20 °C range. Peak velocity and power decline by only 10%–19% with a 10 °C drop, compared to >42% for nonelastic, muscle-powered tongue retraction. These results indicate that the elastic recoil mechanism circumvents the constraints that low temperature imposes on muscle rate properties and thereby reduces the thermal dependence of tongue projection. We propose that organisms that use elastic recoil mechanisms for ecologically important movements such as feeding and locomotion may benefit from an expanded thermal niche.
Identifying the roles of race-based choice and chance in high school friendship network formation
Authors: Currarini Sergio , Jackson Matthew O. , Pin Paolo
Published: March 2010

Homophily, the tendency of people to associate with others similar to themselves, is observed in many social networks, ranging from friendships to marriages to business relationships, and is based on a variety of characteristics, including race, age, gender, religion, and education. We present a technique for distinguishing two primary sources of homophily: biases in the preferences of individuals over the types of their friends and biases in the chances that people meet individuals of other types. We use this technique to analyze racial patterns in friendship networks in a set of American high schools from the Add Health dataset. Biases in preferences and biases in meeting rates are both highly significant in these data, and both types of biases differ significantly across races. Asians and Blacks are biased toward interacting with their own race at rates >7 times higher than Whites, whereas Hispanics exhibit an intermediate bias in meeting opportunities. Asians exhibit the least preference bias, valuing friendships with other types 90% as much as friendships with Asians, whereas Blacks and Hispanics value friendships with other types 55% and 65% as much as same-type friendships, respectively, and Whites fall in between, valuing other-type friendships 75% as much as friendships with Whites. Meetings are significantly more biased in large schools (>1,000 students) than in small schools (<1,000 students), and biases in preferences exhibit some significant variation with the median household income levels in the counties surrounding the schools.
Evolutionary games in the multiverse
Authors: Gokhale Chaitanya S. , Traulsen Arne
Published: March 2010

Evolutionary game dynamics of two players with two strategies has been studied in great detail. These games have been used to model many biologically relevant scenarios, ranging from social dilemmas in mammals to microbial diversity. Some of these games may, in fact, take place between a number of individuals and not just between two. Here we address one-shot games with multiple players. As long as we have only two strategies, many results from two-player games can be generalized to multiple players. For games with multiple players and more than two strategies, we show that statements derived for pairwise interactions no longer hold. For two-player games with any number of strategies there can be at most one isolated internal equilibrium. For any number of players

with any number of strategies

, there can be at most

isolated internal equilibria. Multiplayer games show a great dynamical complexity that cannot be captured based on pairwise interactions. Our results hold for any game and can easily be applied to specific cases, such as public goods games or multiplayer stag hunts.
Intercalation as a means to suppress cyclization and promote polymerization of base-pairing oligonucleotides in a prebiotic world
Authors: Horowitz Eric D. , Engelhart Aaron E. , Chen Michael C. , Quarles Kaycee A. , Smith Michael W. , Lynn David G. , Hud Nicholas V.
Published: March 2010

The RNA world hypothesis proposes that nucleic acids were once responsible for both information storage and chemical catalysis, before the advent of coded protein synthesis. However, it is difficult to imagine how nucleic acid polymers first appeared, as the abiotic chemical formation of long nucleic acid polymers from mononucleotides or short oligonucleotides remains elusive, and barriers to achieving this goal are substantial. One specific obstacle to abiotic nucleic acid polymerization is strand cyclization. Chemically activated short oligonucleotides cyclize efficiently, which severely impairs polymer growth. We show that intercalation, which stabilizes and rigidifies nucleic acid duplexes, almost totally eliminates strand cyclization, allowing for chemical ligation of tetranucleotides into duplex polymers of up to 100 base pairs in length. In contrast, when these reactions are performed in the absence of intercalators, almost exclusively cyclic tetra- and octanucleotides are produced. Intercalator-free polymerization is not observed, even at tetranucleotide concentrations > 10,000-fold greater than those at which intercalators enable polymerization. We also demonstrate that intercalation-mediated polymerization is most favored if the size of the intercalator matches that of the base pair; intercalators that bind to Watson–Crick base pairs promote the polymerization of oligonucleotides that form these base pairs. Additionally, we demonstrate that intercalation-mediated polymerization is possible with an alternative, non-Watson–Crick-paired duplex that selectively binds a complementary intercalator. These results support the hypothesis that intercalators (acting as ‘molecular midwives’) could have facilitated the polymerization of the first nucleic acids and possibly helped select the first base pairs, even if only trace amounts of suitable oligomers were available.
Characterization of somatic cell nuclear reprogramming by oocytes in which a linker histone is required for pluripotency gene reactivation
Authors: Jullien Jerome , Åstrand Carolina , Halley-Stott Richard P. , Garrett Nigel , Gurdon John B.
Published: March 2010

When transplanted into
Xenopus
oocytes, the nuclei of mammalian somatic cells are reprogrammed to express stem cell genes such as
Oct4
,
Nanog
, and
Sox2
. We now describe an experimental system in which the pluripotency genes
Sox2
and
Oct4
are repressed in retinoic acid-treated ES cells but are reprogrammed up to 100% within 24 h by injection of nuclei into the germinal vesicle (GV) of growing
Xenopus
oocytes. The isolation of GVs in nonaqueous medium allows the reprogramming of individual injected nuclei to be seen in real time. Analysis using fluorescence recovery after photobleaching shows that nuclear transfer is associated with an increase in linker histone mobility. A simultaneous loss of somatic H1 linker histone and incorporation of the oocyte-specific linker histone B4 precede transcriptional reprogramming. The loss of H1 is not required for gene reprogramming. We demonstrate both by antibody injection experiments and by dominant negative interference that the incorporation of B4 linker histone is required for pluripotency gene reactivation during nuclear reprogramming. We suggest that the binding of oocyte-specific B4 linker histone to chromatin is a key primary event in the reprogramming of somatic nuclei transplanted to amphibian oocytes.
Kinetochore alignment within the metaphase plate is regulated by centromere stiffness and microtubule depolymerases
Authors: Jaqaman Khuloud , King Emma M. , Amaro Ana C. , Winter Jennifer R. , Dorn Jonas F. , Elliott Hunter L. , Mchedlishvili Nunu , McClelland Sarah E. , Porter Iain M. , Posch Markus , Toso Alberto , Danuser Gaudenz , McAinsh Andrew D. , Meraldi Patrick , Swedlow Jason R.
Published: March 2010

During mitosis in most eukaryotic cells, chromosomes align and form a metaphase plate halfway between the spindle poles, about which they exhibit oscillatory movement. These movements are accompanied by changes in the distance between sister kinetochores, commonly referred to as breathing. We developed a live cell imaging assay combined with computational image analysis to quantify the properties and dynamics of sister kinetochores in three dimensions. We show that baseline oscillation and breathing speeds in late prometaphase and metaphase are set by microtubule depolymerases, whereas oscillation and breathing periods depend on the stiffness of the mechanical linkage between sisters. Metaphase plates become thinner as cells progress toward anaphase as a result of reduced oscillation speed at a relatively constant oscillation period. The progressive slowdown of oscillation speed and its coupling to plate thickness depend nonlinearly on the stiffness of the mechanical linkage between sisters. We propose that metaphase plate formation and thinning require tight control of the state of the mechanical linkage between sisters mediated by centromeric chromatin and cohesion.
Atomistic methods in fluid simulation
Authors: Kadau Kai , Barber John L. , Germann Timothy C. , Holian Brad L. , Alder Berni J.
Published: March 2010

Atomistic methods, such as molecular dynamics and direct simulation Monte Carlo, constitute a powerful and growing set of techniques for fluid-dynamics simulation. The more fundamental nature of such methods, which exhibit nonlinear transport effects and small-scale fluctuations, extends their modelling accuracy to a significantly wider range of scales and regimes than the more traditional Navier–Stokes-based continuum fluid-simulation techniques. In this paper, we describe the current state of the art in atomistic fluid simulation, from both a theoretical and a computational standpoint, and outline the advantages and limitations of such methods. In addition, we present an overview of some recent atomistic-simulation results on fluid instabilities and on the physical scaling of atomistic techniques. Finally, we suggest possible avenues of future research in the field.
Magnetorotational instability: recent developments
Authors: Julien Keith , Knobloch Edgar
Published: March 2010

The magnetorotational instability is believed to play an important role in accretion disc physics in extracting angular momentum from the disc and allowing accretion to take place. For this reason the instability has been the subject of numerous numerical simulations and, increasingly, laboratory experiments. In this review, recent developments in both areas are surveyed, and a new theoretical approach to understanding the nonlinear processes involved in the saturation of the instability is outlined.
The interplay between helicity and rotation in turbulence: implications for scaling laws and small-scale dynamics
Authors: Pouquet A. , Mininni P. D.
Published: March 2010

Invariance properties of physical systems govern their behaviour: energy conservation in turbulence drives a wide distribution of energy among modes, as observed in geophysical or astrophysical flows. In ideal hydrodynamics, the role of the invariance of helicity (correlation between velocity and its curl, measuring departures from mirror symmetry) remains unclear since it does not alter the energy spectrum. However, in the presence of rotation, significant differences emerge between helical and non-helical turbulent flows. We first briefly outline some of the issues such as the partition of energy and helicity among modes. Using massive numerical simulations, we then show that small-scale structures and their intermittency properties differ according to whether helicity is present or not, in particular with respect to the emergence of Beltrami core vortices that are laminar helical vertical updraft vortices. These results point to the discovery of a small parameter besides the Rossby number, a fact that would relate the problem of rotating helical turbulence to that of critical phenomena, through the renormalization group and weak-turbulence theory. This parameter can be associated with the adimensionalized ratio of the energy to helicity flux to small scales, the three-dimensional energy cascade being weak and self-similar.
Small Atwood number Rayleigh–Taylor experiments
Authors: Andrews Malcolm J. , Dalziel Stuart B.
Published: March 2010

Consideration is given to small Atwood number (non-dimensional density difference) experiments to investigate mixing driven by Rayleigh–Taylor (R–T) instability. The past 20 years have seen the development of novel experiments to investigate R–T mixing and, simultaneously, the advent of high-fidelity diagnostics. Indeed, the developments of experiments and diagnostics have gone hand in hand, and as a result modern R–T experiments rival the capabilities and research scope of shear-driven mixing experiments. Thus, research into the small Atwood number limit has made significant progress over the past 20 years, and has offered important insights into natural mixing processes as well as the general R–T problem. This review of small Atwood number experiments serves as an opportunity to discuss progress, and also to provoke thoughts about future high Atwood number designs and difficulties.
Review of theoretical modelling approaches of Rayleigh–Taylor instabilities and turbulent mixing
Authors: Abarzhi Snezhana I.
Published: March 2010

We review the theoretical developments in the field of Rayleigh–Taylor instabilities and turbulent mixing, discuss what is known and what is not known about the phenomenon, and outline the features of similarity of the turbulent mixing process. Based on the physical intuition and on the results of rigorous theoretical studies, we put forward some new ideas on how to grasp the essentials of the mixing process and consider the influence of momentum transport on the invariants and on scaling and statistical properties of the unsteady turbulent mixing.
Feeding patterns of sitatunga (Tragelaphus Speki) in the Rushebeya‐Kanyabaha wetland, south western Uganda
Authors: Tweheyo Mnason , Amanya Bruce Kacebonaho , Turyahabwe Nelson
Published: March 2010

Feeding patterns and habits of sitatunga were assessed in Rushebeya‐Kanyabaha wetland between June 2006 and July 2007. Sixty transects were cut at intervals of 250 m along which sitatunga dung piles, habitats used and diet were identified from feeding signs or plant damage. Household interviews were also conducted in villages adjacent to the wetland to understand plants and crops known to be fed on by sitatunga, type of damage, frequency of sitatunga farm visits and their methods to control crop raiding. Sitatunga mostly fed on leaves (60%) and in the wetland edge (WE) habitat (49%). Forty plant species were recorded to be eaten with herbs as majority (33%) and of crops sweet potatoes were most raided. Sitatungas are basically solitary species with 73% of the sightings being of a single individual. They had mornings and late evenings as their movement peaks and preferred to feed on broad leaved plants. There were significant relationships between both habitat use and food preferences with seasons. We predict that because of seasonal food variations, crop raiding would increase and may result into more negative attitudes by farmers to sitatunga. More research on farmers’ sensitization, population census, behaviours and ecotourism are necessary for this species conservation.
Wound infiltration for surgery
Authors: Scott N. B.
Published: March 2010

Wound infiltration with local anaesthetics is a simple, effective and inexpensive means of providing good analgesia for a variety of surgical procedures without any major side‐effects. In particular, local anaesthetic toxicity, wound infection and healing do not appear to be major considerations. The purpose of this review is to outline the existing literature on a procedure‐specific basis and to encourage a more widespread acceptance of the technique, ensuring that all layers are infiltrated in a controlled and meticulous manner.
Upper limb blocks
Authors: Russon K. , Pickworth T. , Harrop‐Griffiths W.
Published: March 2010

This article discusses recent innovations and changes in practice in upper limb regional anaesthesia, dividing the blocks into those performed above the clavicle, those performed in the area of the clavicle and those performed below it. It offers a critical appraisal of the current status with regard to the use of ultrasound nerve location for upper limb regional anaesthesia and, while accepting that the use of ultrasound in this way has many theoretical advantages and will therefore continue to grow, concludes that there is currently insufficient published evidence to determine conclusively that the use of this technique is associated with nerve blocks that are more successful or safer.