bluuebunny/crossref_metadata_2025 huggingface dataset:
Biophysical and Physiological Origins of Blood Oxygenation Level-Dependent fMRI Signals
Authors: Kim Seong-Gi , Ogawa Seiji
Published: March 2012

After its discovery in 1990, blood oxygenation level-dependent (BOLD) contrast in functional magnetic resonance imaging (fMRI) has been widely used to map brain activation in humans and animals. Since fMRI relies on signal changes induced by neural activity, its signal source can be complex and is also dependent on imaging parameters and techniques. In this review, we identify and describe the origins of BOLD fMRI signals, including the topics of (1) effects of spin density, volume fraction, inflow, perfusion, and susceptibility as potential contributors to BOLD fMRI, (2) intravascular and extravascular contributions to conventional gradient-echo and spin-echo BOLD fMRI, (3) spatial specificity of hemodynamic-based fMRI related to vascular architecture and intrinsic hemodynamic responses, (4) BOLD signal contributions from functional changes in cerebral blood flow (CBF), cerebral blood volume (CBV), and cerebral metabolic rate of O2 utilization (CMRO2), (5) dynamic responses of BOLD, CBF, CMRO2, and arterial and venous CBV, (6) potential sources of initial BOLD dips, poststimulus BOLD undershoots, and prolonged negative BOLD fMRI signals, (7) dependence of stimulus-evoked BOLD signals on baseline physiology, and (8) basis of resting-state BOLD fluctuations. These discussions are highly relevant to interpreting BOLD fMRI signals as physiological means.
Large Enhancement of Perfusion Contribution on fMRI Signal
Authors: Wang Xiao , Zhu Xiao-Hong , Zhang Yi , Chen Wei
Published: March 2012

The perfusion contribution to the total functional magnetic resonance imaging (fMRI) signal was investigated using a rat model with mild hypercapnia at 9.4 T, and human subjects with visual stimulation at 4 T. It was found that the total fMRI signal change could be approximated as a linear superposition of ‘true’ blood oxygenation level-dependent (BOLD; T2/T2*) effect and the blood flow-related ( T1) effect. The latter effect was significantly enhanced by using short repetition time and large radiofrequency pulse flip angle and became comparable to the ‘true’ BOLD signal in response to a mild hypercapnia in the rat brain, resulting in an improved contrast-to-noise ratio (CNR). Bipolar diffusion gradients suppressed the intravascular signals but had no significant effect on the flow-related signal. Similar results of enhanced fMRI signal were observed in the human study. The overall results suggest that the observed flow-related signal enhancement is likely originated from perfusion, and this enhancement can improve CNR and the spatial specificity for mapping brain activity and physiology changes. The nature of mixed BOLD and perfusion-related contributions in the total fMRI signal also has implication on BOLD quantification, in particular, the BOLD calibration model commonly used to estimate the change of cerebral metabolic rate of oxygen.
Use of Spectral Analysis with Iterative Filter for Voxelwise Determination of Regional Rates of Cerebral Protein Synthesis with L-[1-11C]leucine PET
Authors: Veronese Mattia , Schmidt Kathleen C , Smith Carolyn Beebe , Bertoldo Alessandra
Published: March 2012

A spectral analysis approach was used to estimate kinetic parameters of the L-[1-11C]leucine positron emission tomography (PET) method and regional rates of cerebral protein synthesis ( rCPS) on a voxel-by-voxel basis. Spectral analysis applies to both heterogeneous and homogeneous tissues; it does not require prior assumptions concerning number of tissue compartments. Parameters estimated with spectral analysis can be strongly affected by noise, but numerical filters improve estimation performance. Spectral analysis with iterative filter (SAIF) was originally developed to improve estimation of leucine kinetic parameters and rCPS in region-of-interest (ROI) data analyses. In the present study, we optimized SAIF for application at the voxel level. In measured L-[1-11C]leucine PET data, voxel-level SAIF parameter estimates averaged over all voxels within a ROI (mean voxel-SAIF) generally agreed well with corresponding estimates derived by applying the originally developed SAIF to ROI time-activity curves (ROI-SAIF). Region-of-interest-SAIF and mean voxel-SAIF estimates of rCPS were highly correlated. Simulations showed that mean voxel-SAIF rCPS estimates were less biased and less variable than ROI-SAIF estimates in the whole brain and cortex; biases were similar in white matter. We conclude that estimation of rCPS with SAIF is improved when the method is applied at voxel level than in ROI analysis.
A Quantitative Model for Human Olfactory Receptors
Authors: Hassan Sk. Sarif , Pal Choudhury Pabitra , Bose Aritra
Published: March 2012

A wide variety of chemicals having distinct odors are smelled by humans. Odor perception initiates in the nose, where it is detected by a large family of olfactory receptors (ORs). Based on divergence of evolutionary model, a sequence of human ORs database has been proposed by D. Lancet et al (2000, 2006). It is quite impossible to infer whether a given sequence of nucleotides is a human OR or not, without any biological experimental validation. In our perspective, a proper quantitative understanding of these ORs is required to justify or nullify whether a given sequence is a human OR or not. In this paper, all human OR sequences have been quantified, and a set of clusters have been made using the quantitative results based on two different metrics. Using this proposed quantitative model, one can easily make probable justification or deterministic nullification whether a given sequence of nucleotides is a probable human OR homologue or not, without seeking any biological experiment. Of course a further biological experiment is essential to validate the probable human OR homologue.
Improving metabolite evaluation in integrated pathway analysis
Authors: Kaur Rasanpreet , Dutta Anwesha , Kutmon Martina , Iersel Martijn , Evelo Chris
Published: March 2012

Biological molecules such as proteins and metabolites interact to accomplish a biological function and to respond to environmental stimuli. Pathways capture this information derived through scientific experimentation and data analysis. They contain information about genes that appear in complexes, the interacting genes, the directionality of the interactions (e.g. inhibitors versus activators), the cellular locations where the reactions occur, and the metabolites that are affected by the processes. Using our open-source pathway analysis platform, PathVisio, we will connect pathway analysis to different quantitative approaches already in development for metabolic network modeling, such as flux balance analysis and dynamic simulation. In order to use system-wide measurements to gain insights into this mechanism, we have to integrate large scale data analysis with modeled or measured fluxomics data results. For this we will develop a BridgeDb database for reaction identifiers, develop a PathVisio plugin for visualization of modeling results and architect a flexible, standards-based visualization approach (e.g. using MIM and SBGN) that will enable visualization of any conforming model, including visualization of the model output (e.g. flux changes). The focus here is on visualization of the modeling results, which will be critical for understanding how simulated models correlate with experimental measurements On the same lines, we will also find a solution to the problem of annotating metabolites in all pathways. The approach here is to use known Gene Ontology annotations for associated genes. Firstly we will incorporate automatically inferred GO categories into all WikiPathways. Develop GO visualization plugin to show gene categories on pathways and further assign automatically inferred GO categories to all addressable metabolites in WikiPathways. The last step would be to develop basic metabolite ontology analysis tools both with python GUIs and as Bioconductor modules.
Weight Loss Induced by Chronic Dapagliflozin Treatment Is Attenuated by Compensatory Hyperphagia in Diet‐Induced Obese (DIO) Rats
Authors: Devenny James J. , Godonis Helen E. , Harvey Susan J. , Rooney Suzanne , Cullen Mary J. , Pelleymounter Mary Ann
Published: March 2012

Dapagliflozin is a potent and selective sodium glucose cotransporter‐2 (SGLT2) inhibitor which promotes urinary glucose excretion and induces weight loss. Since metabolic compensation can offset a negative energy balance, we explored the potential for a compensatory physiological response to the weight loss induced by dapagliflozin. Dapagliflozin was administered (0.5–5 mpk; p.o.) to diet‐induced obese (DIO) rats with or without ad libitum access to food for 38 days. Along with inducing urinary glucose excretion, chronic administration of dapagliflozin dose‐dependently increased food and water intake relative to vehicle‐treated controls. Despite this, it reduced body weight by 4% (relative to controls) at the highest dose. The degree of weight loss was increased by an additional 9% if hyperphagia was prevented by restricting food intake to that of vehicle controls. Neither oxygen consumption (vO2) or the respiratory exchange ratio (RER) were altered by dapagliflozin treatment alone. Animals treated with dapagliflozin and pair‐fed to vehicle controls (5 mpk PF‐V) showed a reduction in RER and an elevation in nonfasting β‐hydroxybutyrate (BHBA) relative to ad libitum‐fed 5 mpk counterparts. Fasting BHBA was elevated in the 1 mpk, 5 mpk, and 5 mpk PF‐V groups. Serum glucose was reduced in the fasted, but not the unfasted state. Insulin was reduced in the non‐fasted state. These data suggest that in rodents, the persistent urinary glucose excretion induced by dapagliflozin was accompanied by compensatory hyperphagia, which attenuated the weight loss induced by SGLT2 inhibition. Therefore, it is possible that dapagliflozin‐induced weight loss could be enhanced with dietary intervention.
Cyanide is an adequate agonist of the plant hormone ethylene for studying signalling of sensor kinase ETR1 at the molecular level
Authors: Bisson Melanie M. A. , Groth Georg
Published: March 2012

The plant hormone ethylene is involved in many developmental processes and responses to environmental stresses in plants. Although the elements of the signalling cascade and the receptors operating the ethylene pathway have been identified, a detailed understanding of the molecular processes related to signal perception and transfer is still lacking. Analysis of these processes using purified proteins in physical, structural and functional studies is complicated by the gaseous character of the plant hormone. In the present study, we show that cyanide, a π-acceptor compound and structural analogue of ethylene, is a suitable substitute for the plant hormone for in vitro studies with purified proteins. Recombinant ethylene receptor protein ETR1 (ethylene-resistant 1) showed high level and selective binding of [14C]cyanide in the presence of copper, a known cofactor in ethylene binding. Replacement of Cys65 in the ethylene-binding domain by serine dramatically reduced binding of radiolabelled cyanide. In contrast with wild-type ETR1, autokinase activity of the receptor is not reduced in the ETR1-C65S mutant upon addition of cyanide. Additionally, protein–protein interaction with the ethylene signalling protein EIN2 (ethylene-insensitive 2) is considerably sustained by cyanide in wild-type ETR1, but is not affected in the mutant. Further evidence for the structural and functional equivalence of ethylene and cyanide is given by the fact that the ethylene-responsive antagonist silver, which is known to allow ligand binding but prevent intrinsic signal transduction, also allows specific binding of cyanide, but shows no effect on autokinase activity and ETR1–EIN2 interaction.
Acute and chronic effects of bupivacaine on muscle energetics during contraction in vivo: a modular metabolic control analysis
Authors: Arsac Laurent M. , Nouette-Gaulain Karine , Miraux Sylvain , Deschodt-Arsac Veronique , Rossignol Rodrigue , Thiaudiere Eric , Diolez Philippe
Published: March 2012

Bupivacaine is a widely used anaesthetic injected locally in clinical practice for short-term neurotransmission blockade. However, persistent side effects on mitochondrial integrity have been demonstrated in muscle parts surrounding the injection site. We use the precise language of metabolic control analysis in the present study to describe in vivo consequences of bupivacaine injection on muscle energetics during contraction. We define a model system of muscle energy metabolism in rats with a sciatic nerve catheter that consists of two modules of reactions, ATP/PCr (phosphocreatine) supply and ATP/PCr demand, linked by the common intermediate PCr detected in vivo by 31P-MRS (magnetic resonance spectroscopy). Measured system variables were [PCr] (intermediate) and contraction (flux). We first applied regulation analysis to quantify acute effects of bupivacaine. After bupivacaine injection, contraction decreased by 15.7% and, concomitantly, [PCr] increased by 11.2%. The regulation analysis quantified that demand was in fact directly inhibited by bupivacaine (−21.3%), causing an increase in PCr. This increase in PCr indirectly reduced mitochondrial activity (−22.4%). Globally, the decrease in contractions was almost fully explained by inhibition of demand (−17.0%) without significant effect through energy supply. Finally we applied elasticity analysis to quantify chronic effects of bupivacaine iterative injections. The absence of a difference in elasticities obtained in treated rats when compared with healthy control rats clearly shows the absence of dysfunction in energetic control of muscle contraction energetics. The present study constitutes the first and direct evidence that bupivacaine myotoxicity is compromised by other factors during contraction in vivo, and illustrates the interest of modular approaches to appreciate simple rules governing bioenergetic systems when affected by drugs.
Spin and elastic contributions to isothermal entropy change
Authors: Mukherjee T. , Skomski R. , Michalski S. , Sellmyer D. J. , Binek Ch.
Published: March 2012

Statistical considerations of ensembles of localized magnetic moments reveal an upper bound of the isothermal entropy change when only the magnetic degrees of freedom are considered. In this case, the maximum molar isothermal entropy change is determined by the spin multiplicity and is equal to Rln(2J + 1), where J is the angular momentum of an individual atom. However, in materials with giant magnetocaloric effect, the isothermal field-induced entropy change goes beyond the spin-multiplicity limit due to field-activated elastic degrees of freedom. Recently, we investigated a model of pairs of exchange-coupled Ising spins with variable real-space positions. We showed, within a classical approximation for the elastic degree of freedom, that a vibrational entropy contribution can be activated via applied magnetic fields. Here we quantify the impact of quantum corrections in the low-temperature limit. We compare calculations that include elastic interaction with the rigid exchange model in the high-temperature limit. We find that quantum effects provide quantitative corrections in the low-temperature limit. In addition we show that the elastic contributions to the isothermal entropy change can be additive but, remarkably, it can also give rise to reduced isothermal entropy change in certain temperature regions.
Size- and phase-controlled synthesis of cobalt nanoparticles for potential biomedical applications
Authors: Osorio-Cantillo C. , Santiago-Miranda A. N. , Perales-Perez O. , Xin Y.
Published: March 2012

The present work addresses the synthesis and characterization of crystalline cobalt nanoparticles produced through a modified polyol-process conducive to the controlled formation of magnetic soft-Co structures with potential for applications in biomedicine. XRD characterization evidenced the influence of oleate and acetate species on the formation and crystal growth-inhibition of crystalline fcc-Co with controlled average crystallite sizes in the 8–10nm range. Magnetic measurements confirmed the strong influence of synthesis conditions on crystal structure and hence, on magnetic properties. As-synthesized nanoparticles exhibited coercivity values below 100 Oe and magnetization as high as 155 emu/g at room temperature. These values agreed with the soft magnetic nature of the fcc-Co phase.
The optimization of dual-core closed-loop fluxgate technology in precision current sensor
Authors: Yang Xiaoguang , Zhang Bo , Wang Youhua , Zhao Zhigang , Yan Weili
Published: March 2012

This paper presents a new dual-core closed-loop flux gate current sensor. The mathematical model was built, and the parameters that affect the characteristics of the flux gate current sensor were analyzed. The effects of the structural parameters on output characteristics of the sensor were simulated. Based on the simulation results, a prototype was designed, and the test results have a good agreement with the simulation results. The current sensor has the advantages of ultra low nonlinear error ( ± 3‰) and low offset error. The noise in the primary current is eliminated when measuring dc or ac signal. Especially, the designed dual-core closed-loop flux gate current sensor can measure current up to 20 kHz with the nominal primary current value of ± 30 A.
Microscopic dipole-exchange theory for magnonic crystals: Application to ferromagnetic films with patterned surfaces
Authors: Nguyen Hoa T. , Cottam Michael G.
Published: March 2012

Calculations are reported for the spin-wave bands and gaps in magnonic crystals formed by patterning one (or both) of the surfaces of ferromagnetic thin films. Specifically, a patterning in terms of a periodic array of rectangular grooves is considered, and the theory employs a microscopic (or Hamiltonian-based) method that incorporates exchange and magnetic dipole–dipole interactions, as well as an external magnetic field. The coupling between different periodic elements of the magnonic crystal involves both exchange and dipolar terms, allowing for control of the spin-wave bands and gaps as the depth and width of the grooves are varied. Numerical examples are given for Permalloy structures, considering the stripe patterning to be on one or two surfaces, and the applicability to Brillouin light scattering is discussed.
Electron spin resonance and magnetization studies on Bi0.5Ca0.5Mn0.95TM0.05O3 (TM = Cr, Fe, Co and Ni)
Authors: Vijayan D. , Kurian Joji , Singh R.
Published: March 2012

In this work, we present the temperature dependent ESR and magnetization measurements on 3d TM doped Bi-manganite samples of composition Bi0.5Ca0.5Mn0.95TM0.05O3 (TM = Cr, Fe, Co and Ni) synthesized by solid state reaction method. The temperature dependent double integrated intensity (DI) of the ESR signal and the magnetic moment (M) have been used to estimate the charge ordering temperature (TCO), antiferromagnetic ordering (AFM) onset temperature TO and Neel temperature, TN. The 1/DI and 1/M versus T plots show FM correlations in the temperature range T > TCO and coexistence of ferromagnetic (FM) and AFM correlations in the temperature range TCO > T > TO. The magnetization data give TCO values close to the values obtained from ESR data. The data are analyzed in view of electronic phase separation model. The suppression of charge ordering is explained in view of the changes in short range magnetic interactions between Mn ions and the possible change in the band structure as a result of TM ion doping.
Magnetic properties and high-frequency characteristics of FeCoAlO gradient composition thin films
Authors: Zheng Fu , Luo Feilong , Lou Yuanfu , Wang Ying , Bai Jianmin , Wei Dan , Liu Xiaoxi , Wei Fulin
Published: March 2012

5 × 25 mm FeCoAlO gradient composition thin film was prepared with composite target by using RF magnetron sputtering. The Al-O composition gradient along the length direction of the film was introduced by Al2O3 chips asymmetrically arrayed on a Fe70Co30 target disk. The film was divided into five equal segments. All samples showed a low coercive force Hc of 4 – 8 Oe. The saturation magnetization 4πMs increased continuously from 17.3 kGs for sample 1 (has more Al-O content) to 19.7 kGs for sample 5 and it was consistent with the increasing of Fe-Co composition. Meanwhile, these samples showed different anisotropy behaviors relating with Al-O composition. The sample 1 exhibited the same magnetization curve along the directions of G‖ and G⊥ (G‖ and G⊥ are parallel and perpendicular to the direction of the Al-O composition gradient, respectively). In both of G‖ & G⊥ directions, the sample 1 showed a resonance frequency (fr) of around 2.6 – 3.0 GHz, while, in G‖ direction, it showed a high value of real permeability μ′. The sample 5 exhibited a distinct in-plane uniaxial anisotropy and a good high-frequency response of 3.0 GHz resonance frequency. So these films having gradient composition exhibit are suggested for the use in integrated magnetic devices working in the GHz frequency range.
Magnetic properties of Y0.9Gd0.1Fe2D4.2 compound under continuous magnetic field up to 310 kOe
Authors: Paul-Boncour V. , Guillot M. , Mazet T.
Published: March 2012

In this work are presented results on the structural, magnetic, and magnetocaloric properties of the Y0.9Gd0.1Fe2D4.2 compound in which TM0 is shifted from 84 K to 110 K because of Gd influence. Magnetization measurements have been performed with a magnetic field up to 310 kOe in the 4.2–300 K temperature range with special attention paid near TM0. The spontaneous magnetization at 4.2 K (3.2 μB/mol) is smaller than for YFe2D4.2 (3.7 μB/mol), showing the contribution of Gd moments. Above 110 K, metamagnetic field-induced transitions are observed: the transition field HTR increases linearly with T. These transitions exist up to 170 K. The influence of both cell volume change and Gd magnetic contribution are finally discussed in comparison with other deuterides.
Ferromagnetic microstructures in the ferromagnetic metallic phase of La0.825Sr0.175MnO3
Authors: Koyama T. , Togawa Y. , Takenaka K. , Mori S.
Published: March 2012

Ferromagnetic (FM) microstructures in the FM metallic phase of La0.825Sr0.175MnO3 were examined by means of Lorentz transmission electron microscopy (Lorentz TEM) and small-angle electron diffraction (SAED). Microstructures of FM domains depend strongly on the crystal structures. The structural phase transition at 185 K accompanies with a drastic change of 180 degree FM domain structures from macroscopic wide domains to striped narrow domains. Lorentz TEM and SAED experiments revealed that a distribution of the magnetization in the striped FM domains is non-uniform and locally fluctuated.
Exchange bias in sputtered FM/BiFeO3 thin films (FM = Fe and Co)
Authors: Chang H. W. , Yuan F. T. , Shih C. W. , Li W. L. , Chen P. H. , Wang C. R. , Chang W. C. , Jen S. U.
Published: March 2012

Magnetic properties of sputter-deposited ferromagnetic (FM)/BiFeO3 (BFO) films on Pt/Ti/SiO2/Si(100) substrate (FM = Co and Fe) have been investigated. Isotropic perovskite BFO single phase is obtained for 200-nm-thick BFO films deposited at 300–450 °C and BFO films at 400 °C with thickness of 50–400 nm. Large exchange bias field (HEB) of 308–400 Oe and coercivity (Hc) of 1201–3632 Oe at RT are obtained for polycrystalline Co/BFO bilayers. The roughened surface induced by high deposition temperature and increasing thickness of BFO layer enhances localized shape anisotropy of FM layer, resulting in the increase of Hc the improved crystallinity and roughened surface of BFO/Co interface might be responsible for the HEB enhancement. Additionally, comparison on the HEB in polycrystalline Co/BFO and Fe/BFO systems is also discussed.
Gravity-oriented microfluidic device for uniform and massive cell spheroid formation
Authors: Lee Kangsun , Kim Choong , Young Yang Jae , Lee Hun , Ahn Byungwook , Xu Linfeng , Yoon Kang Ji , Oh Kwang W.
Published: March 2012

We propose a simple method for forming massive and uniform three-dimensional (3-D) cell spheroids in a multi-level structured microfluidic device by gravitational force. The concept of orienting the device vertically has allowed spheroid formation, long-term perfusion, and retrieval of the cultured spheroids by user-friendly standard pipetting. We have successfully formed, perfused, and retrieved uniform, size-controllable, well-conditioned spheroids of human embryonic kidney 293 cells (HEK 293) in the gravity-oriented microfluidic device. We expect the proposed method will be a useful tool to study in-vitro 3-D cell models for the proliferation, differentiation, and metabolism of embryoid bodies or tumours.
An eddy viscosity model for two-dimensional breaking waves and its validation with laboratory experiments
Authors: Tian Zhigang , Perlin Marc , Choi Wooyoung
Published: March 2012

An eddy viscosity model to describe energy dissipation in two-dimensional breaking waves in deep water is implemented in a numerical model for the evolution of nonlinear surface waves and evaluated with experimental results. In the experiments, to develop a reliable eddy viscosity model, breaking waves are generated by both energy focusing and modulated wave groups. Local wave parameters prior to and following breaking are defined and then determined. Significant correlations between the pre-breaking and post-breaking parameters are identified and adopted in the eddy viscosity model. The numerical model detects automatically wave breaking onset based on local surface slope, determines pre-breaking local wave parameters, predicts post-breaking time and length scales, and estimates eddy viscosity to dissipate energy in wave breaking events. Numerical simulations with the model are performed and compared to the experiments. It is found that the model predicts well the total energy dissipation due to breaking waves. In addition, the computed surface elevations after wave breaking agree reasonably well with the measurements for the energy focusing (plunging) wave groups. However, for breaking wave groups due to modulational instability (plunging and spilling), a relatively large discrepancy between the surface elevation predictions and the experimental measurements is observed, in particular, at the downstream wave probe locations. This is possibly due to wave reflection and three-dimensionality in the experiments. To further validate the eddy viscosity model, the evolution of highly nonlinear irregular waves is studied numerically and the numerical solutions are compared with additional independent laboratory experiments for long-crested irregular waves. It is shown that the numerical model is capable of predicting the wave evolution subsequent to wave breaking.
A micromagnetic study of the reversal mechanism in permalloy antidot arrays
Authors: Van de Wiele B. , Manzin A. , Vansteenkiste A. , Bottauscio O. , Dupré L. , De Zutter D.
Published: March 2012

A numerical analysis is focused on the influence of patterning and finite-size effects on the hysteresis properties and magnetization reversal of permalloy antidot films with square lattice and square holes. Simulations are performed by solving the Landau-Lifshitz equation. The aim is to explain the relationships between the shape of the hysteresis loop and the different stages of the reversal process. In particular, the switching mechanism is characterized by the nucleation of domain chains that destroy the periodic symmetry in the magnetization present when infinite periodicity is considered. This behavior is strongly influenced by the demagnetizing effects arising both at the film boundaries and at the hole edges.
A calorimetric method to detect a weak or distributed latent heat contribution at first order magnetic transitions
Authors: Morrison K. , Bratko M. , Turcaud J. , Berenov A. , Caplin A. D. , Cohen L. F.
Published: March 2012

Microcalorimetry has proven to be a versatile tool to investigate first order magnetic phase transitions as it can be used in different experimental modes to separate the latent heat from heat capacity. However, the methodology fails if the latent heat contribution is below instrumental resolution of 10 nJ. If the nucleation size of the new phase is much less than 100 μm, the typical size of the fragment measured, the latent heat could appear to be too distributed in temperature or magnetic field to be detected. Here, we show that for certain classes of magnetic transition, our microcalorimetry technique can be extended to enable an estimate of the latent heat to be obtained from a combination of heat capacity and magnetic measurements. This technique is best suited for material systems with weakly first order phase transitions, or highly distributed due to inhomogeneity.
Frequency tuning the ultrafast magnetization dynamics of FexPt100-x alloys
Authors: Brandt R. , Ganss F. , Senn T. , Daniel M. , Albrecht M. , Schmidt H.
Published: March 2012

We report frequency tuning of magnetic oscillations in both planar films and individual patterned nano-sized dots by varying the iron content of disordered FexPt100-x alloys from 42 at. % to 100 at. %. It is seen that as the Fe content is increased, the magnetic oscillation frequency rises by up to 50% in both the films and individual dots due to the change in the saturation magnetization. Micromagnetic simulations and analytic calculations are in agreement with the data. These tunable alloys could be used in microwave-assisted magnetic recording and especially for developing a 3D storage technology where layers of different resonance frequency are switched individually.
Temperature and frequency dependencies of the switching field in glass-coated FeNbSiB microwires
Authors: Sabol R. , Varga R. , Hudak J. , Blazek J. , Praslicka D. , Vojtanik P. , Badini G. , Vazquez M.
Published: March 2012

We are dealing with the temperature and frequency dependencies of the switching field in the glass-coated FeNbSiB microwire. Both dependencies can be described in terms of two contributions to the switching mechanism: magnetoelastic and structural relaxation. We show that by properly setting the frequency of the measurement, it is possible to vary the relative strength of both contributions. Hence, the temperature dependence of the switching field can be tailored according to desired conditions being temperature independent for low (<100 Hz) and high (>500 Hz) frequencies or almost linearly dependent for medium frequency ∼350 Hz.
Surface processing technique based on opto-hydrodynamic phenomena occurring in laser-induced breakdown of a microdroplet
Authors: Ahn Daehwan , Jang Deoksuk , Choi Tae-Youl , Kim Dongsik
Published: March 2012

We report the development of a surface processing technique based on the optical breakdown of a microdroplet and subsequent ejection of a pulsed microjet. The microjet was sufficiently fast to remove nanoparticles from surfaces and erode most materials. The small volume of the droplet enabled precise and selective treatment of surfaces. When the jet was impinged onto a laser spot focused by the droplet, ablation rates substantially larger than those in conventional pulsed laser ablation were obtained with significantly reduced thermal effects. The jet could remove 20 nm particles and an oxide layer from solid surfaces by hydrodynamic impact only.
Top-to-bottom optimization of the optical performance of the tandem organic solar cells with thin metal film as interlayer
Authors: Long Yongbing , Shen Liang , Ruan Shenping , Yu Wenjuan , Wang Yi , Zeng Qingguang , Luo Jianyi
Published: March 2012

Top-to-bottom optimization is developed to maximize the absorption for tandem organic solar cells with thin Ag interlayer connecting two subcells. By redshifting the cavity modes of the microcavity between the Ag interlayer and the top electrode, the absorption spectrum of the top cell can be shifted to the near-infrared wavelength range where the bottom cell has weak absorption. Correspondingly, subcells with highly complementary absorption spectrum are achieved, and there is an improvement of 17.8% in the total absorbed photons for the tandem device. Additionally, it is revealed that high transparency is not an essential property for the interlayer in tandem devices.
Direct measurement of the three-dimensional magnetization vector trajectory in GaMnAs by a magneto-optical pump-and-probe method
Authors: Tesařová N. , Němec P. , Rozkotová E. , Šubrt J. , Reichlová H. , Butkovičová D. , Trojánek F. , Malý P. , Novák V. , Jungwirth T.
Published: March 2012

We report on a quantitative experimental determination of the three-dimensional magnetization vector trajectory in GaMnAs by means of the static and time-resolved pump-and-probe magneto-optical measurements. The experiments are performed in a normal incidence geometry and the time evolution of the magnetization vector is obtained without any numerical modeling of magnetization dynamics. Our experimental method utilizes different polarization dependences of the polar Kerr effect and magnetic linear dichroism to disentangle the pump-induced out-of-plane and in-plane motions of magnetization, respectively. We demonstrate that the method is sensitive enough to allow for the determination of small angle excitations of the magnetization in GaMnAs. The method is readily applicable to other magnetic materials with sufficiently strong circular and linear magneto-optical effects.
Semiclassical Monte Carlo simulation studies of spin dephasing in InP and InSb nanowires
Authors: Kumar Ashish , Akram M. W. , Ghosh Bahniman
Published: March 2012

We use semiclassical Monte Carlo approach to investigate spin polarized transport in InP and InSb nanowires. D’yakonov-Perel (DP) relaxation and Elliott-Yafet (EY) relaxation are the two main relaxation mechanisms for spin dephasing in III-V channels. The DP relaxation occurs because of bulk inversion asymmetry (Dresselhaus spin-orbit interaction) and structural inversion asymmetry (Rashba spin-orbit interaction). The injection polarization direction studied is that along the length of the channel. The dephasing rate is found to be very strong for InSb as compared to InP which has larger spin dephasing lengths. The ensemble averaged spin components vary differently for both InP and InSb nanowires. The steady state spin distribution also shows a difference between the two III-V nanowires.
Genotypic variation in in sacco dry matter degradation kinetics in perennial ryegrass (Lolium perenne L.)
Authors: Sun X. Z. , Waghorn G. C. , Hatier J.-H. B. , Easton H. S.
Published: March 2012

Fast degrading perennial ryegrass (Lolium perenne L.) is a desirable characteristic to select for because it can result in increased feed intake by grazing ruminants. Sufficient range in genotypic variation of dry matter (DM) degradation kinetics is a prerequisite for selection. To investigate the genotypic variation, 77 perennial ryegrass accessions sourced internationally, grown in autumn in the same conditions and harvested in the vegetative state, were examined using an in sacco technique. From the time course of DM disappearance, soluble fraction ‘A’, potentially degradable fraction ‘B’, indigestible fraction ‘C’ and the degradation rate k of fraction ‘B’ were estimated. The results indicated that a large range in genotypic variation was present in all degradation parameters. Fraction ‘A’ ranged from 0.48 to 0.60, with the highest five accessions being 21% higher than the lowest five. Degradation rate k of fraction ‘B’ ranged from 0.069 to 0.199/h, with the fastest five being 125% higher than the slowest five. There were no strong correlations between degradation parameters and chemical composition. In conclusion, there was considerable genotypic variation in DM degradation kinetics among perennial ryegrass accessions and this presents plant breeders with ample opportunity to select for fast degrading perennial ryegrasses.
The current and future projected distribution of Solanum hoplopetalum (Solanaceae): an indigenous weed of the south-western Australian grain belt
Authors: Michael Pippa J. , Yeoh Paul B. , Scott John K.
Published: March 2012

The factors determining the distribution of the Western Australian endemic Solanum hoplopetalum Bitter & Summerh. (Solanaceae) were assessed because it was identified as a potential weed risk to Australian cropping regions, including under climate change scenarios. Incubation at constant temperatures determined daily plant growth rates and plants required 1380 degree-days above a threshold of 12.4°C to complete growth to flowering. From this and published information on the plant’s biology, we developed a mechanistic niche model using CLIMEX. The model projection for current climates produced a highly significant match to known distribution records. Spatially, the lower south-west and areas eastwards to South Australia, western New South Wales and southern parts of the Northern Territory were climatically suitable for growth of S. hoplopetalum. However, by 2070 the area under risk decreases, with the projected distribution under climate change contracting southwards. We hypothesise that climatic extremes and edaphic factors, possibly high soil pH, may be major factors determining the current distribution of S. hoplopetalum. Containment on the southern edge of the current distribution, interstate quarantine and local eradication in new areas of invasion are recommended as management options to combat the potential for this native weed to spread.
Polycomb repressive complex 2 is required for MLL-AF9 leukemia
Authors: Neff Tobias , Sinha Amit U. , Kluk Michael J. , Zhu Nan , Khattab Mohamed H. , Stein Lauren , Xie Huafeng , Orkin Stuart H. , Armstrong Scott A.
Published: March 2012

A growing body of data suggests the importance of epigenetic mechanisms in cancer. Polycomb repressive complex 2 (PRC2) has been implicated in self-renewal and cancer progression, and its components are overexpressed in many cancers. However, its role in cancer development and progression remains unclear. We used conditional alleles for the PRC2 components enhancer of zeste 2 (
Ezh2
) and embryonic ectoderm development (
Eed
) to characterize the role of PRC2 function in leukemia development and progression. Compared with wild-type leukemia,
Ezh2
-null MLL-AF9–mediated acute myeloid leukemia (AML) failed to accelerate upon secondary transplantation. However,
Ezh2
-null leukemias maintained self-renewal up to the third round of transplantation, indicating that
Ezh2
is not strictly required for MLL-AF9 AML, but plays a role in leukemia progression. Genome-wide analyses of PRC2-mediated trimethylation of histone 3 demonstrated locus-specific persistence of H3K27me3 despite inactivation of
Ezh2
, suggesting partial compensation by
Ezh1
. In contrast, inactivation of the essential PRC2 gene,
Eed
, led to complete ablation of PRC2 function, which was incompatible with leukemia growth. Gene expression array analyses indicated more profound gene expression changes in
Eed
-null compared with
Ezh2
-null leukemic cells, including down-regulation of Myc target genes and up-regulation of PRC2 targets. Manipulating PRC2 function may be of therapeutic benefit in AML.
The Rapid Establishment, Dispersal, and Increased Abundance of Invasive American Shad in the Pacific Northwest
Authors: Hasselman Daniel J , Hinrichsen Richard A , Shields Barbara A , Ebbesmeyer Curtis C
Published: March 2012

American shad (Alosa sapidissima) were repeatedly introduced into two Pacific coastal rivers in the late 1800s. They rapidly established, dispersed, and expanded their range over 5,000 km of coastline from Mexico to Russia. American shad also increased dramatically in abundance and now comprise the largest spawning run of anadromous fish in the Columbia River (>4 million fish annually). Despite constituting a remarkable biological invasion, invasive shad have not been the subject of much scientific investigation and remain relatively obscure in the Pacific Northwest. In this first of two complementary articles, we attempt to raise the profile of invasive American shad among fisheries professionals and generate scientific interest in this biological invasion. We provide an overview of the history of their introduction and discuss the mechanisms that may have contributed to the species ‘establishment, rapid dispersal along the Pacific coast, and its increased abundance in the Columbia River. In the second accompanying article we discuss the possible ecological consequences of the invasion in Pacific coastal ecosystems but also its inherent value to studies of ecology and evolution. These articles are designed to be read in succession.

RESUMEN

el sábalo americano fue introducido repetidamente en dos ríos costeros del Pacífico hacia finales de 1800. Las poblaciones se establecieron, dispersaron y expandieron rápidamente su rango geográfico a lo largo de 5,000 km de línea de costa, desde México hasta Rusia. El sábalo americano también incrementó considerablemente su abundancia y a la fecha produce la mayor corrida de desove de un pez anádromo en el Río Columbia (> 4 millones de individuos por año). A pesar de que ésta constituye una invasión biológica sorprendente, el sábalo americano no ha sido objeto importante de investigación científica, por lo que la especie permanece relativamente oscura en el Pacífico Noroeste. En estos dos primeros artículos complementarios, se realiza un esfuerzo por elevar el perfil del sábalo americano entre los profesionales de las pesquerías y para generar un interés científico acerca de su invasión. Se brinda un panorama de la historia de su introducción y se discuten los mecanismos que pudieron haber contribuido al establecimiento de la especie, su rápida dispersión a lo largo de la costa del Pacífico y su aumento de abundancia en el Río Columbia. En el segundo artículo se discuten las posibles consecuencias de la invasión en los ecosistemas costeros del Pacífico, pero también su valor inherente para estudios de ecología y evolución. Estos artículos se diseñaron para leerse consecutivamente.
American Shad of the Pacific Coast: A Harmful Invasive Species or Benign Introduction?
Authors: Hasselman Daniel J , Hinrichsen Richard A , Shields Barbara A , Ebbesmeyer Curtis C
Published: March 2012

Research on the ecological effects of aquatic invasive species in North America has largely focused on the Laurentian Great Lakes, with less attention directed to their influence in coastal ecosystems. American shad (Alosa sapidissima) were introduced to the Pacific coast in the late 1800s, rapidly established, dispersed, and became prolific. Despite constituting a remarkable biological invasion, shad in their introduced range have not been the subject of much scientific investigation. The species persists in relative obscurity in the Pacific Northwest and remains ecological overlooked and evolutionarily underappreciated. In this second of two complementary articles, we consider the potential ecological effects of invasive American shad on Pacific coastal ecosystems and the possible consequences for the persistence of native salmonids. We also reflect on the intrinsic value that this invasion provides to studies of ecology and evolution and highlight several areas of research that require immediate investigation if we are to determine whether nonindigenous shad constitute a harmful invasive species or a benign introduction.

RESUMEN

las investigaciones sobre los efectos ecológicos de especies acuáticas invasivas en Norteamérica se ha concentrado principalmente en la región de los grandes lagos, y con menos énfasis en la influencia de dichas especies en ecosistemas costeros. El sábalo americano fue introducido en la costa del Pacífico hacia finales de 1800, donde rápidamente se estableció, dispersó y proliferó. Si bien ésta constituye una invasión biológica notable, el sábalo no ha sido objeto importante de investigación científica dentro de su rango de introducción. La especie persiste en relativo anonimato en el Pacífico, se mantiene ecológicamente desapercibida y evolutivamente poco valorada. En este segundo de dos artículos complementarios, se estudian los efectos potenciales del sábalo americano en los ecosistemas costeros del Pacífico, y las posibles consecuencias de la invasión en los salmónidos nativos a la región. También se discute el valor intrínseco que tiene esta invasión para estudios ecológicos y evolutivos, y se destacan diversas áreas de investigación que requieren de atención inmediata con el fin de determinar en qué medida el sábalo americano representa una invasión nociva o una introducción benéfica.
Comparison of three models of actigraph accelerometers during free living and controlled laboratory conditions
Authors: Lee Ka‐Yiu , Macfarlane Duncan J. , Cerin Ester
Published: March 2012

The aim of this study was to compare the outputs of three commonly used uniaxial Actigraph models (Actitrainer, 7164 and GT1M) under both free‐living and controlled laboratory conditions. Ten adults (mean age = 24.7±1.1 years) wore the three Actigraph models simultaneously during one of day free‐living and during a progressive exercise protocol on a treadmill at speeds between 1.5 and 5.5 miles per hour (mph). During free‐living the three Actigraph models produced comparable outputs in moderate, vigorous and moderate‐to‐vigorous physical activity (MVPA) with effect sizes typically <0.2, but lower comparability was seen in sedentary and light categories, as well as in total step counts (effect sizes often >0.30). In controlled conditions, acceptable comparability between the three models was seen at all treadmill speeds, the exception being walking at 1.5 mph (mean effect size = 0.48). It is concluded that care should be taken if different Actigraph models are to be used to measure and compare light physical activity, step counts and walking at very low speeds. However, using any of these three different Actigraph models to measure and compare levels of MVPA in free‐living adults seems appropriate.
An appreciation of John Pollock's work on the computational study of argument
Authors: Prakken Henry , Horty John
Published: March 2012

John Pollock (1940–2009) was an influential American philosopher who made important contributions to various fields, including epistemology and cognitive science. In the last 25 years of his life, he also contributed to the computational study of defeasible reasoning and practical cognition in artificial intelligence. He developed one of the first formal systems for argumentation-based inference and he put many issues on the research agenda that are still relevant for the argumentation community today. This paper presents an appreciation of Pollock's work on defeasible reasoning and its relevance for the computational study of argument. In our opinion, Pollock deserves to be remembered as one of the founding fathers of the field of computational argument, while, moreover, his work contains important lessons for current research in this field, reminding us of the richness of its object of study.