bluuebunny/crossref_metadata_2025 huggingface dataset:
Current-induced switching of exchange bias in nano-scaled magnetic tunnel junctions with a synthetic antiferromagnetic pinned layer
Authors: Chao C. T. , Kuo C. Y. , Horng Lance , Tsunoda M. , Takahashi M. , Wu J. C.
Published: February 2012

This report investigates the current-induced switching of exchange bias without an external magnetic field in nano-scaled magnetic tunnel junction (MTJ) cells. An MTJ stack film was patterned into an ellipse with dimensions of 120 nm × 270 nm by using standard electron beam lithography in combination with ion beam etching. A spin-polarized current pulse with a duration of 100 ns was used to switch the exchange bias direction of the synthetic antiferromagnetic (SAF) pinned layer. It is worth noting that the MTJ cell was initialized in a high resistance state before applying the current pulse. For the application of both positive and negative current pulses, the resistance can be switched from the high (antiparallel) state to the low (parallel) one at 2.95 and −2.80 mA, respectively. After the current-induced switching, it was found that the magnetoresistance curve is reversed relative to the one before the current-induced switching. Predominantly, this behavior is independent of the polarity of the current pulse. As a result, it is shown that the exchange bias in the SAF pinned layer changes its direction with a sufficient supply of current pulse.
Multiple 360° domain wall switching in thin ferromagnetic nanorings in a circular magnetic field
Authors: Goldman Abby , Licht Abigail S. , Sun Yineng , Li Yihan , Pradhan Nihar R. , Yang Tianyu , Tuominen Mark T. , Aidala Katherine E.
Published: February 2012

Micromagnetic simulations of the vortex switching process of thin ferromagnetic rings under the application of a circular field, as if created from a current-carrying wire passing through the ring center, reveal that for rings with sub-micron dimensions and thicknesses on the order of the exchange length, the vortex to vortex switching process occurs through the nucleation and annihilation of multiple 360° domain walls (DWs). The DWs can be characterized by their circulation relative to the vortex circulation; the DWs form in pairs with opposite topological indices. The DW with the same circulation annihilates first, which has a smaller energy barrier to overcome before annihilating. The contributions from both the exchange energy and demagnetization energy must be considered to predict which DW will annihilate first. Either wall could be annihilated by offsetting the current toward the wall being targeted.
Magnetic tunneling junction with Fe/NiFeB free layer for magnetic logic circuits
Authors: Honjo H. , Fukami S. , Nebashi R. , Ishiwata N. , Miura S. , Sakimura N. , Sugibayashi T. , Kasai N. , Ohno H.
Published: March 2012

We have developed a shape varying magnetic tunneling junction (SVM) with a Fe/NiFeB free layer for use in magnetic logic circuits. Inserting the thin Fe film between an NiFeB free layer and MgO tunneling barrier improved the magnetoresistance (MR) ratio: it increased up to 130%, as the thickness of the Fe film increased. In addition, the switching current distribution of the SVM was reduced to 8%. By using NiFeB as a free layer, the roughness under the MgO was reduced and the crystallization of the MgO was enhanced. This led to both the high MR ratio and the low switching current distribution. Our developed Fe (0.4 nm)/NiFeB free layer satisfies the requirement of the MTJ’s characteristics that the magnetic logic circuits operate with a high bit yield.
Photovoltaic phenomena in BiFeO3 multiferroic ceramics
Authors: Hung C.-M. , Tu C.-S. , Yen W. D. , Jou L. S. , Jiang M.-D. , Schmidt V. H.
Published: March 2012

Open-circuit photovoltage and short-circuit photocurrent were investigated in BiFeO3 (BFO) ceramics as functions of laser wavelength (λ  =  373 and 532 nm), illumination intensity, and sample thickness. BFO ceramics exhibit significant photovoltaic responses under near-ultraviolet illumination of λ = 373 nm. The photovoltaic responses strongly depend on wavelength, light intensity, and sample thickness. The relation between photovoltaic responses and light intensity can be described by exponential equations, EOC = ES[1 – exp(–I/α)] and JSC = JS[1 – exp(−I/β)]. EOC, JSC, ES, and JS are open-circuit photovoltage (V/cm), short-circuit photocurrent density (A/cm2), saturated photovoltage (V/cm), and saturated photocurrent density, respectively. This work suggests that BFO ceramic exhibits stronger photovoltaic responses than the ferroelectric WO3-doped Pb1-xLax(ZryTiz)1-x/4O3 ceramics and Pb(Mg1/3Nb2/3)1-xTixO3 crystals.
Structural and electrical properties of half-Heusler La-Pt-Bi thin films grown by 3-source magnetron co-sputtering
Authors: Miyawaki Tetsuya , Sugimoto Nozomi , Fukatani Naoto , Yoshihara Tatsuhiko , Ueda Kenji , Tanaka Nobuo , Asano Hidefumi
Published: March 2012

Half-Heusler La-Pt-Bi thin films have been deposited on YAlO3(001) substrate by 3-source magnetron co-sputtering. Control of the Bi content was the critical factor to obtain single phase, c-axis-oriented thin films. Generation of secondary phases was effectively prevented by precise control of the deposition rate for separate targets as well as adjustment of the deposition temperature. The realization of single-phase LaPtBi thin films will provide new potential applications to topological insulating devices based on Heusler alloys.
The use of magnetic nanoparticles in thermal therapy monitoring and screening: Localization and imaging (invited)
Authors: Weaver John B.
Published: March 2012

Magnetic nanoparticles have many diagnostic and therapeutic applications. A method termed magnetic spectroscopy of nanoparticle Brownian motion (MSB) was developed to interrogate in vivo the microscopic environment surrounding magnetic nanoparticles. We can monitor several effects that are important in thermal therapy and screening including temperature measurement and the bound state distribution. Here we report on simulations of nanoparticle localization. Measuring the spatial distribution of nanoparticles would allow us to identify ovarian cancer much earlier when it is still curable or monitor thermal therapies more accurately. We demonstrate that with well-designed equipment superior signal to noise ratio (SNR) can be achieved using only two harmonics rather than using all the harmonics containing signal. Alternatively, smaller magnetic field amplitudes can be used to achieve the same SNR. The SNR is improved using fewer harmonics because the noise is limited.
Electric currents induced step-like resistive jumps and negative differential resistance in thin films of Nd0.7Sr0.3MnO3
Authors: Wang J. F. , Wu Z. P. , Gao J.
Published: March 2012

Electric-currents-induced emergent phenomena were found in microbridges of Nd0.7Sr0.3MnO3. After the samples were processed by currents of high densities, a second metal-insulator transition appeared at low temperatures. This resistance peak was very sensitive to weak currents. More salient features were the step-like resistance jumps. At temperatures near these resistance steps, negative differential resistance was observed. Interfacial effects related to electrodes could be ruled out. These effects might be due to current-enhanced inhomogeneity.
Microscopic theory for Gilbert damping in materials with inhomogeneous spin dynamics
Authors: Umetsu Nobuyuki , Miura Daisuke , Sakuma Akimasa
Published: March 2012

We study Gilbert damping in bulk metallic ferromagnets in the presence of nonmagnetic and magnetic impurities. A microscopic expression is obtained for the Gilbert damping parameter using linear response theory with respect to the interaction between magnetization and the conduction electrons in the ferromagnets. In an inhomogeneous precession system, a space-dependent damping torque term of the form ηM×∇r2M· is added to the space-independent term αM×M·. We show that the magnetic impurities contribute to both α and η, but the nonmagnetic impurities to only η in the absence of spin-orbit coupling.
Effects of high pressure on the magnetism of ErCo2
Authors: Míšek Martin , Prokleška Jan , Sechovský Vladimír , Turčinková Dana , Prchal Jiří , Kusmartseva Anna F. , Kamenev Konstantin V. , Kamarád Jiří
Published: March 2012

This paper presents the results of a high pressure study on the ferrimagnetic compound ErCo2, which exhibits at ambient pressure magnetic ordering below TC = 33 K, where the localized Er magnetic moments order ferromagnetically, and the itinerant moments in the Co sublattice, align antiparallel to the Er moments. In the paramagnetic range, clustering of the Co moments is observed below Tf ∼ 100 K for which the term “parimagnetism” has been proposed. In contrast to the pronounced peak in the AC susceptibility data at TC only a tiny “bump” shows up at Tf. The decrease of both TC and Tf with applied hydrostatic pressure has been observed, the first one being in agreement with previously published data. At higher pressures, an asymmetry in the TC-related AC susceptibility peak has been observed owing to a decoupling of the magnetic ordering phenomena in the Er and Co sublattices. Compared to earlier published results, our magnetization measurements at higher pressures above PC reveal a small but clearly observable evolution of both the critical temperature and saturated magnetization.
Spin transport in Au films: An investigation by spin pumping
Authors: Montoya Eric , Kardasz Bartek , Burrowes Capucine , Huttema Wendell , Girt Erol , Heinrich Bret
Published: March 2012

The thickness and temperature dependence of spin transport in Au has been investigated in multilayer films via the spin pumping effect. To study spin transport in Au, single layer GaAs/16Fe/(d)Au(001) and double layer GaAs/16Fe/(d)Au/12Fe/20Au(001) were investigated using ferromagnetic resonance (FMR), where d = 20, 300, and the numerals preceding Fe and Au indicate the layer thickness in atomic layers (AL). FMR measurements were performed at frequencies ranging from 27.3 to 40.6 GHz and at temperatures ranging from 88 to 295 K. By measuring the total Gilbert damping in the 16Fe layer as a function of d and temperature for both single and double magnetic layer structures and by utilizing the spin diffusion equation, one is able to determine the spin mixing conductance, g↑↓, at the Fe/Au interface, and the spin flip relaxation time, τsf, in Au as a function of temperature. The temperature dependence of the momentum relaxation time, τm, in Au was measured independently by means of electron transport measurements in a van der Pauw configuration. It has been found that the spin flip relaxation time, τsf, in Au is dominated by phonon interactions.
Permanent magnet online magnetization performance analysis of a flux mnemonic double salient motor using an improved hysteresis model
Authors: Zhu Xiaoyong , Quan Li , Chen Yunyun , Liu Guohai , Shen Yue , Liu Hui
Published: March 2012

The concept of the memory motor is based on the fact that the magnetization level of the AlNiCo permanent magnet in the motor can be regulated by a temporary current pulse and memorized automatically. In this paper, a new type of memory motor is proposed, namely a flux mnemonic double salient motor drive, which is particularly attractive for electric vehicles. To accurately analyze the motor, an improved hysteresis model is employed in the time-stepping finite element method. Both simulation and experimental results are given to verify the validity of the new method.
Molecular dynamics simulations of charged nanoparticle self-assembly at ionic liquid-water and ionic liquid-oil interfaces
Authors: Frost Denzil S. , Dai Lenore L.
Published: February 2012

Nanoparticle self-assembly at liquid-liquid interfaces can be significantly affected by the individual nanoparticle charges. This is particularly true at ionic liquid (IL) based interfaces, where Coulombic forces play a major role. Employing 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]) as a model IL, we have studied the self-assembly of hydrophobic nanoparticles with different surface charges at the IL/water and IL/oil (hexane) interfaces using molecular dynamics simulations. In the IL/water system, the nanoparticles were initially dispersed in the water phase but quickly equilibrated at the interface, somewhat in favor of the IL phase. This preference was lessened with increased nanoparticle charge. In the IL/hexane system, all charged nanoparticles interacted with the IL to some extent, whereas the uncharged nanoparticles remained primarily in the hexane phase. Potential of mean force calculations supported the observations from the equilibrium studies and provided new insights into the interactions of the nanoparticles and ionic liquid based interfaces.
Conedy: A scientific tool to investigate complex network dynamics
Authors: Rothkegel Alexander , Lehnertz Klaus
Published: February 2012

We present Conedy, a performant scientific tool to numerically investigate dynamics on complex networks. Conedy allows to create networks and provides automatic code generation and compilation to ensure performant treatment of arbitrary node dynamics. Conedy can be interfaced via an internal script interpreter or via a Python module.
Simulation of crack propagation in alumina with ab initio based polarizable force field
Authors: Hocker Stephen , Beck Philipp , Schmauder Siegfried , Roth Johannes , Trebin Hans-Rainer
Published: February 2012

We present an effective atomic interaction potential for crystalline α-Al2O3 generated by the program potfit. The Wolf direct, pairwise summation method with spherical truncation is used for electrostatic interactions. The polarizability of oxygen atoms is included by use of the Tangney-Scandolo interatomic force field approach. The potential is optimized to reproduce the forces, energies, and stresses in relaxed and strained configurations as well as {0001}, $\lbrace 10\overline{1}0\rbrace${101¯0}, and $\lbrace 11\overline{2}0\rbrace${112¯0} surfaces of Al2O3. Details of the force field generation are given, and its validation is demonstrated. We apply the developed potential to investigate crack propagation in α-Al2O3 single crystals.
Nuclear spin selective laser control of rotational and torsional dynamics
Authors: Floß J. , Grohmann T. , Leibscher M. , Seideman T.
Published: February 2012

We explore the possibility of controlling rotational-torsional dynamics of non-rigid molecules with strong, non-resonant laser pulses and demonstrate that transient, laser-induced torsional alignment depends on the nuclear spin of the molecule. Consequently, nuclear spin isomers can be manipulated selectively by a sequence of time-delayed laser pulses. We show that two pulses with different polarization directions can induce either overall rotation or internal torsion, depending on the nuclear spin. Nuclear spin selective control of the angular momentum distribution may open new ways to separate and explore nuclear spin isomers of polyatomic molecules.
In situ multifrequency ferromagnetic resonance and x-ray magnetic circular dichroism investigations on Fe/GaAs(110): Enhanced g-factor
Authors: Römer F. M. , Möller M. , Wagner K. , Gathmann L. , Narkowicz R. , Zähres H. , Salles B. R. , Torelli P. , Meckenstock R. , Lindner J. , Farle M.
Published: March 2012

We determined the magnetic anisotropy energy and g-factor of an uncapped 10 nm thick Fe/GaAs(110) film using a setup that allows frequency (1.5–26.5 GHz) as well as angular dependent ferromagnetic resonance measurements under ultrahigh vacuum conditions. The g-factor g=2.61±0.1 is unusually high at room temperature and can be interpreted as the result of an increased orbital moment due to strain. This interpretation is supported by more surface sensitive x-ray magnetic circular dichroism measurements which yield g=2.21±0.02 measured at remanence. The difference in g may be the result of magnetic field dependent magnetostriction which influences the orbital moment.
Dipolar response of hydrated proteins
Authors: Matyushov Dmitry V.
Published: February 2012

The paper presents an analytical theory and numerical simulations of the dipolar response of hydrated proteins in solution. We calculate the effective dielectric constant representing the average dipole moment induced at the protein by a uniform external field. The dielectric constant shows a remarkable variation among the proteins, changing from 0.5 for ubiquitin to 640 for cytochrome c. The former value implies a negative dipolar susceptibility, that is a dia-electric dipolar response and negative dielectrophoresis. It means that ubiquitin, carrying an average dipole of ≃240 D, is expected to repel from the region of a stronger electric field. This outcome is the result of a negative cross-correlation between the protein and water dipoles, compensating for the positive variance of the intrinsic protein dipole in the overall dipolar susceptibility. In contrast to the neutral ubiquitin, charged proteins studied here show para-electric dipolar response and positive dielectrophoresis. The study suggests that the dipolar response of proteins in solution is strongly affected by the coupling of the protein surface charge to the hydration water. The protein-water dipolar cross-correlations are long-ranged, extending ∼2 nm from the protein surface into the bulk. A similar correlation length of about 1 nm is seen for the electrostatic potential produced by the hydration water inside the protein. The analysis of numerical simulations suggests that the polarization of the protein-water interface is highly heterogeneous and does not follow the standard dielectric results for cavities carved in dielectrics. The polarization of the water shell gains in importance, relative to the intrinsic protein dipole, at high frequencies, above the protein Debye peak. The induced interfacial dipole can be either parallel or antiparallel to the protein dipole, depending on the distribution of the protein surface charge. As a result, the high-frequency absorption of the protein solution can be either higher or lower than the absorption of water. Both scenarios have been experimentally observed in the THz window of radiation.
Asymptotic integral kernel for ensembles of random normal matrices with radial potentials
Authors: Veneziani Alexei M. , Pereira Tiago , Marchetti Domingos H. U.
Published: February 2012

The method of steepest descent is used to study the integral kernel of a family of normal random matrix ensembles with eigenvalue distribution \documentclass[12pt]{minimal}\begin{document}$P_{N}(z_{1},\cdots ,z_{N})=Z_{N}^{-1}\emph {e}^{-N\sum _{i=1}^{N}V_{\alpha }(z_{i})}\prod _{1\le i<j\le N}\left|z_{i}-z_{j}\right|^{2},$\end{document}PN(z1,⋯,zN)=ZN−1e−N∑i=1NVα(zi)∏1≤i<j≤Nzi−zj2,where Vα(z) = |z|α, \documentclass[12pt]{minimal}\begin{document}$z\in \mathbb {C}$\end{document}z∈C and α ∈ ]0, ∞[. Asymptotic formulas with error estimate on sectors are obtained. A corollary of these expansions is a scaling limit for the n-point function in terms of the integral kernel for the classical Segal–Bargmann space.
Ab initio calculation of lattice dynamics and thermodynamic properties of beryllium
Authors: Luo Fen , Cai Ling-Cang , Chen Xiang-Rong , Jing Fu-Qian , Alfè Dario
Published: March 2012

We investigate the phase transition, elastic constants, phonon dispersion curves, and thermal properties of beryllium (Be) at high pressures and high temperatures using density functional theory. By comparing the Gibbs free energy, in the quasiharmonic approximation (QHA), of hexagonal-closed-packed (hcp) with those of the face-centered cubic (fcc) and body-centered-cubic (bcc) we find that the hcp Be is stable up to 390 GPa, and then transforms to the bcc Be. The calculated phonon dispersion curves are in excellent agreement with experiments. Under compression, the phonon dispersion curves of hcp Be do not show any anomaly or instability. At low pressure the phonon dispersion of bcc Be display imaginary along Γ-N in the T1 branches. Within the quasiharmonic approximation, we predict the thermal equation of state and other properties including the thermal expansion coefficient, Hugoniot curves, heat capacity, Grüneisen parameter, and Debye temperature.
Direct observation of potassium ions in HeLa cell with ion-selective nano-pipette probe
Authors: Takami Tomohide , Iwata Futoshi , Yamazaki Koji , Wan Son Jong , Lee Joo-Kyung , Ho Park Bae , Kawai Tomoji
Published: February 2012

The local concentration of potassium ion in a single HeLa cell was observed with an ion-selective nano-pipette probe. Ion selectivity was achieved by using a polyvinyl chloride film with selected ionophores placed within the nano-pipette. Both alternating and constant bias voltages were applied to the counter electrode for the observation of local ion concentrations with a response time of less than 0.1 s. These measurements were enabled by a low-current detection system prepared specifically for this study. The difference in local potassium concentrations between inside a living HeLa cell and the surrounding solution was approximately 100 mM, while no difference in potassium ion concentration was observed between the interior of dead cells and the surrounding solution.
Ultraviolet versus infrared: Effects of ablation laser wavelength on the expansion of laser-induced plasma into one-atmosphere argon gas
Authors: Ma Qianli , Motto-Ros Vincent , Laye Fabrice , Yu Jin , Lei Wenqi , Bai Xueshi , Zheng Lijuan , Zeng Heping
Published: March 2012

Laser-induced plasma from an aluminum target in one-atmosphere argon background has been investigated with ablation using nanosecond ultraviolet (UV: 355 nm) or infrared (IR: 1064 nm) laser pulses. Time- and space-resolved emission spectroscopy was used as a diagnostics tool to have access to the plasma parameters during its propagation into the background, such as optical emission intensity, electron density, and temperature. The specific feature of nanosecond laser ablation is that the pulse duration is significantly longer than the initiation time of the plasma. Laser-supported absorption wave due to post-ablation absorption of the laser radiation by the vapor plume and the shocked background gas plays a dominant role in the propagation and subsequently the behavior of the plasma. We demonstrate that the difference in absorption rate between UV and IR radiations leads to different propagation behaviors of the plasma produced with these radiations. The consequence is that higher electron density and temperature are observed for UV ablation. While for IR ablation, the plasma is found with lower electron density and temperature in a larger and more homogenous axial profile. The difference is also that for UV ablation, the background gas is principally evacuated by the expansion of the vapor plume as predicted by the standard piston model. While for IR ablation, the background gas is effectively mixed to the ejected vapor at least hundreds of nanoseconds after the initiation of the plasma. Our observations suggest a description by laser-supported combustion wave for the propagation of the plasma produced by UV laser, while that by laser-supported detonation wave for the propagation of the plasma produced by IR laser. Finally, practical consequences of specific expansion behavior for UV or IR ablation are discussed in terms of analytical performance promised by corresponding plasmas for application with laser-induced breakdown spectroscopy.
Excitations of surface plasmon polaritons in double layer metal grating structures
Authors: Anttu N. , Guan Z. Q. , Håkanson U. , Xu H. X. , Xu H. Q.
Published: March 2012

We study the light scattering properties of double layer gratings (DLGs) made from Au on SiO2 substrates. It is found that surface plasmon polaritons (SPPs) can be excited in the DLGs for a separation of up to 150 nm between the two Au grating layers and the collective reflectance spectra exhibit a strong resonant peak and a closely lying dip as a result of the surface plasmon polariton excitations. It is also found that the angle-resolved specular reflectance spectra show a dip-peak pair structure, while the angle-resolved reflectance spectra of higher diffracted orders show a complementary peak-dip pair structure. Finally, operation of the DLGs for efficient wavelength demultiplexing is proposed and discussed in light of these results.
Deposition of epitaxial BiFeO3/CoFe2O4 nanocomposites on (001) SrTiO3 by combinatorial pulsed laser deposition
Authors: Aimon Nicolas M. , Hun Kim Dong , Kyoon Choi Hong , Ross C. A.
Published: February 2012

BiFeO3/CoFe2O4 (BFO/CFO) nanocomposites were grown on SrTiO3 by pulsed laser deposition using a combinatorial method in which Bi1.2FeO3 and CoFe2O4 targets are alternately ablated. The films had the same vertically nanostructured morphology as thin films prepared by ablation of a single target, consisting of epitaxial CoFe2O4 pillars in a BiFeO3 matrix. In a series of samples synthesized with a compositional spread, the out-of-plane magnetic anisotropy and the out-of-plane compressive strain of the CoFe2O4 pillars increased with decreasing volume fraction, and the anisotropy agreed with the value predicted from the strain state and magnetoelastic coefficients of CoFe2O4. These results show the dominant effect of magnetoelastic anisotropy in determining the magnetic hysteresis of the nanocomposite.
Extraordinary acoustic reflection enhancement by acoustically transparent thin plates
Authors: He Zhaojian , Peng Shasha , Hao Rui , Qiu Chunyin , Ke Manzhu , Mei Jun , Liu Zhengyou
Published: February 2012

We report an observation of the extraordinary high reflection of acoustic waves in water by thin epoxy plates partitioned by subwavelength cuts, whereas such plates without structure are acoustically transparent as the acoustic properties of epoxy are close to water. It is demonstrated that this exotic phenomenon results from the resonant excitation of the local modes within the individual pieces derived by the cuts. The experiment agrees well with the theory. Potential applications of such simple structures can be anticipated, e.g., in blocking sound.
Visualization of the conductive channel in a planar resistance switching device based on electrochromic materials
Authors: Shang Da Shan , Shi Lei , Sun Ji-Rong , Shen Bao-Gen
Published: March 2012

In this work, bipolar resistance switching behavior was realized in an Au/tungsten oxide/Au planar device, and the evolution of the conductive channel during resistance switching was successfully visualized by the in situ optical image technique based on the color-conductivity dependence of tungsten oxide. We found that there are two types of conductive channel, named parabolic channel and bar-like channel, exist in the planar device. The parabolic channel formed firstly near the cathode and then extended to but could not touch the anode. By applying opposite electric-field, the bar-like channel formed from the cathode (i.e., foregoing anode) and extended to the parabolic channel. With alternating the external electric-field polarity, the bar-like channel showed an indirect connection and nonmonotonic disconnection with the parabolic channel at the region near the foregoing anode, corresponding to the high-to-low and low-to-high resistance switching processes of the planar device, respectively. The instable RS behavior was caused by the change of bar-like channel occurring position under the high external field condition. The conductive channel formation was ascribed to the sodium ion immersion from the soda-lime glass substrate into the tungsten oxide film and then migration driven by the electric field to form sodium tungsten bronze. These results will give some insight into the resistance switching property improvement and mechanism elucidation as well as a possibility to develop electric/optical-coupled switch and data storage devices.
Metal-enhanced fluorescence: The role of quantum yield, Q, in enhanced fluorescence
Authors: Dragan Anatoliy I. , Geddes Chris D.
Published: March 2012

Metal-enhanced fluorescence has attracted enormous research and commercial interest in recent years, due to the ability to significantly enhance fluorescence signatures in the near-field as well as protect fluorophores against photobleaching. In this article, we address one of the major unresolved questions, whether far-field fluorophore quantum yield, Q0, has a direct relationship to fluorescence enhancement factors in metal-enhanced fluorescence.
Carbon stocks in Tasmanian soils
Authors: Cotching W. E.
Published: February 2012

Soil carbon (C) stocks were calculated for Tasmanian soil orders to 0.3 and 1.0 m depth from existing datasets. Tasmanian soils have C stocks of 49–117 Mg C/ha in the upper 0.3 m, with Ferrosols having the largest soil C stocks. Mean soil C stocks in agricultural soils were significantly lower under intensive cropping than under irrigated pasture. The range in soil C within soil orders indicates that it is critical to determine initial soil C stocks at individual sites and farms for C accounting and trading purposes, because the initial soil C content will determine if current or changed management practices are likely to result in soil C sequestration or emission. The distribution of C within the profile was significantly different between agricultural and forested land, with agricultural soils having two-thirds of their soil C in the upper 0.3 m, compared with half for forested soils. The difference in this proportion between agricultural and forested land was largest in Dermosols (0.72 v. 0.47). The total amount of soil C in a soil to 1.0 m depth may not change with a change in land use, but the distribution can and any change in soil C deeper in the profile might affect how soil C can be managed for sequestration. Tasmanian soil C stocks are significantly greater than those in mainland states of Australia, reflecting the lower mean annual temperature and higher precipitation in Tasmania, which result in less oxidation of soil organic matter.
Evolution in coyotes (Canis latrans) in response to the megafaunal extinctions
Authors: Meachen Julie A. , Samuels Joshua X.
Published: February 2012

Living coyotes modify their behavior in the presence of larger carnivores, such as wolves. However, little is known about the effects of competitor presence or absence on morphological change in coyotes or wolves over long periods of time. We examined the evolution of coyotes and wolves through time from the late Pleistocene, during which many large carnivorous species coexisted as predators and competitors, to the Recent; this allowed us to investigate evolutionary changes in these species in response to climate change and megafaunal extinctions at the end of the Pleistocene. We measured postcranial skeletal morphologies of wolves (Canis lupus) and coyotes (C. latrans) from Pleistocene-aged tar deposits, as well as early, mid, and recent Holocene populations of both. We found few morphological differences between Pleistocene and Holocene wolf populations. Conversely, we found many differences in coyotes: Pleistocene coyotes were larger and more robust than Holocene populations. However, within 1,000 y of the megafaunal extinctions, coyotes are morphologically indistinguishable from modern populations. We cannot attribute these differences directly to climate change because modern coyotes do not follow Bergmann's rule, which states body size increases with decreasing temperature. Instead, we suggest that Pleistocene coyotes may have been larger and more robust in response to larger competitors and a larger-bodied prey base. Although we cannot separate competition from predator-prey interactions, this study indicates that the effects of biotic interactions can be detected in the fossil record.
Plague and landscape resilience in premodern Iceland
Authors: Streeter Richard , Dugmore Andrew J. , Vésteinsson Orri
Published: February 2012

In debates on societal collapse, Iceland occupies a position of precarious survival, defined by not becoming extinct, like Norse Greenland, but having endured, sometimes by the narrowest of margins. Classic decline narratives for late medieval to early modern Iceland stress compounding adversities, where climate, trade, political domination, unsustainable practices, and environmental degradation conspire with epidemics and volcanism to depress the Icelanders and turn the once-proud Vikings and Saga writers into one of Europe's poorest nations. A mainstay of this narrative is the impact of incidental setbacks such as plague and volcanism, which are seen to have compounded and exacerbated underlying structural problems. This research shows that this view is not correct. We present a study of landscape change that uses 15 precisely dated tephra layers spanning the whole 1,200-y period of human settlement in Iceland. These tephras have provided 2,625 horizons of known age within 200 stratigraphic sections to form a high-resolution spatial and temporal record of change. This finding shows short-term (50 y) declines in geomorphological activity after two major plagues in A.D. 15th century, variations that probably mirrored variations in the population. In the longer term, the geomorphological impact of climate changes from the 14th century on is delayed, and landscapes (as well as Icelandic society) exhibit resilience over decade to century timescales. This finding is not a simple consequence of depopulation but a reflection of how Icelandic society responded with a scaling back of their economy, conservation of core functionality, and entrenchment of the established order.
Structure and function of a serine carboxypeptidase adapted for degradation of the protein synthesis antibiotic microcin C7
Authors: Agarwal Vinayak , Tikhonov Anton , Metlitskaya Anastasia , Severinov Konstantin , Nair Satish K.
Published: March 2012

Several classes of naturally occurring antimicrobials exert their antibiotic activity by specifically targeting aminoacyl-tRNA synthetases, validating these enzymes as drug targets. The aspartyl tRNA synthetase “Trojan horse” inhibitor microcin C7 (McC7) consists of a nonhydrolyzable aspartyl-adenylate conjugated to a hexapeptide carrier that facilitates active import into bacterial cells through an oligopeptide transport system. Subsequent proteolytic processing releases the toxic compound inside the cell. Producing strains of McC7 must protect themselves against autotoxicity that may result from premature processing. The
mccF
gene confers resistance against endogenous and exogenous McC7 by hydrolyzing the amide bond that connects the peptide and nucleotide moieties of McC7. We present here crystal structures of MccF, in complex with various ligands. The MccF structure is similar to that of dipeptide
ld
-carboxypeptidase, but with an additional loop proximal to the active site that serves as the primary determinant for recognition of adenylated substrates. Wild-type MccF only hydrolyzes the naturally occurring aspartyl phosphoramidate McC7 and synthetic peptidyl sulfamoyl adenylates that contain anionic side chains. We show that substitutions of two active site MccF residues result in a specificity switch toward aromatic aminoacyl–adenylate substrates. These results suggest how MccF-like enzymes may be used to avert various toxic aminoacyl–adenylates that accumulate during antibiotic biosynthesis or in normal metabolism of the cell.
Rapid creation of
Arabidopsis
doubled haploid lines for quantitative trait locus mapping
Authors: Seymour Danelle K. , Filiault Daniele L. , Henry Isabelle M. , Monson-Miller Jennifer , Ravi Maruthachalam , Pang Andy , Comai Luca , Chan Simon W. L. , Maloof Julin N.
Published: February 2012

Quantitative trait loci (QTL) mapping is a powerful tool for investigating the genetic basis of natural variation. QTL can be mapped using a number of different population designs, but recombinant inbred lines (RILs) are among the most effective. Unfortunately, homozygous RIL populations are time consuming to construct, typically requiring at least six generations of selfing starting from a heterozygous F
1
. Haploid plants produced from an F
1
combine the two parental genomes and have only one allele at every locus. Converting these sterile haploids into fertile diploids (termed “doubled haploids,” DHs) produces immortal homozygous lines in only two steps. Here we describe a unique technique for rapidly creating recombinant doubled haploid populations in
Arabidopsis thaliana
: centromere-mediated genome elimination. We generated a population of 238 doubled haploid lines that combine two parental genomes and genotyped them by reduced representation Illumina sequencing. The recombination rate and parental allele frequencies in our population are similar to those found in existing RIL sets. We phenotyped this population for traits related to flowering time and for petiole length and successfully mapped QTL controlling each trait. Our work demonstrates that doubled haploid populations offer a rapid, easy alternative to RILs for
Arabidopsis
genetic analysis.
Inhibition of Stabilin-2 elevates circulating hyaluronic acid levels and prevents tumor metastasis
Authors: Hirose Yoshikazu , Saijou Eiko , Sugano Yasuyoshi , Takeshita Fumitaka , Nishimura Satoshi , Nonaka Hidenori , Chen Yen-Rong , Sekine Keisuke , Kido Taketomo , Nakamura Takashi , Kato Shigeaki , Kanke Toru , Nakamura Koji , Nagai Ryozo , Ochiya Takahiro , Miyajima Atsushi
Published: February 2012

Hyaluronic acid (HA) has been implicated in the proliferation and metastasis of tumor cells. However, most previous studies were conducted on extracellular matrix or pericellular HA, and the role of circulating HA in vivo has not been studied. HA is rapidly cleared from the bloodstream. The scavenger receptor Stabilin-2 (Stab2) is considered a major clearance receptor for HA. Here we report a dramatic elevation in circulating HA levels in Stab2-deficient mice without any overt phenotype. Surprisingly, the metastasis of B16F10 melanoma cells to the lungs was markedly suppressed in the Stab2-deficient mice, whereas cell proliferation was not affected. Furthermore, administration of an anti-Stab2 antibody in Stab2
+
mice elevated serum HA levels and prevented the metastasis of melanoma to the lung, and also suppressed spontaneous metastasis of mammary tumor and human breast tumor cells inoculated in the mammary gland. Administration of the antibody or high-dose HA in mice blocked the lodging of melanoma cells to the lungs. Furthermore, HA at high concentrations inhibited the rolling/tethering of B16 cells to lung endothelial cells. These results suggest that blocking Stab2 function prevents tumor metastasis by elevating circulating HA levels. Stab2 may be a potential target in antitumor therapy.
Sonic Hedgehog-activated engineered blood vessels enhance bone tissue formation
Authors: Rivron Nicolas C. , Raiss Christian C. , Liu Jun , Nandakumar Anandkumar , Sticht Carsten , Gretz Norbert , Truckenmüller Roman , Rouwkema Jeroen , van Blitterswijk Clemens A.
Published: March 2012

Large bone defects naturally regenerate via a highly vascularized tissue which progressively remodels into cartilage and bone. Current approaches in bone tissue engineering are restricted by delayed vascularization and fail to recapitulate this stepwise differentiation toward bone tissue. Here, we use the morphogen Sonic Hedgehog (Shh) to induce the in vitro organization of an endothelial capillary network in an artificial tissue. We show that endogenous Hedgehog activity regulates angiogenic genes and the formation of vascular lumens. Exogenous Shh further induces the in vitro development of the vasculature (vascular lumen formation, size, distribution). Upon implantation, the in vitro development of the vasculature improves the in vivo perfusion of the artificial tissue and is necessary to contribute to, and enhance, the formation of de novo mature bone tissue. Similar to the regenerating callus, the artificial tissue undergoes intramembranous and endochondral ossification and forms a trabecular-like bone organ including bone-marrow-like cavities. These findings open the door for new strategies to treat large bone defects by closely mimicking natural endochondral bone repair.
Noonan syndrome-causing SHP2 mutants inhibit insulin-like growth factor 1 release via growth hormone-induced ERK hyperactivation, which contributes to short stature
Authors: Serra-Nédélec Audrey De Rocca , Edouard Thomas , Tréguer Karine , Tajan Mylène , Araki Toshiyuki , Dance Marie , Mus Marianne , Montagner Alexandra , Tauber Maïté , Salles Jean-Pierre , Valet Philippe , Neel Benjamin G. , Raynal Patrick , Yart Armelle
Published: February 2012

Noonan syndrome (NS), a genetic disease caused in half of cases by activating mutations of the tyrosine phosphatase SHP2 (
PTPN11
), is characterized by congenital cardiopathies, facial dysmorphic features, and short stature. How mutated SHP2 induces growth retardation remains poorly understood. We report here that early postnatal growth delay is associated with low levels of insulin-like growth factor 1 (IGF-1) in a mouse model of NS expressing the D61G mutant of SHP2. Conversely, inhibition of SHP2 expression in growth hormone (GH)-responsive cell lines results in increased IGF-1 release upon GH stimulation. SHP2-deficient cells display decreased ERK1/2 phosphorylation and rat sarcoma (RAS) activation in response to GH, whereas expression of NS-associated SHP2 mutants results in ERK1/2 hyperactivation in vitro and in vivo. RAS/ERK1/2 inhibition in SHP2-deficient cells correlates with impaired dephosphorylation of the adaptor Grb2-associated binder-1 (GAB1) on its RAS GTPase-activating protein (RASGAP) binding sites and is rescued by interfering with RASGAP recruitment or function. We demonstrate that inhibition of ERK1/2 activation results in an increase of IGF-1 levels in vitro and in vivo, which is associated with significant growth improvement in NS mice. In conclusion, NS-causing SHP2 mutants inhibit GH-induced IGF-1 release through RAS/ERK1/2 hyperactivation, a mechanism that could contribute to growth retardation. This finding suggests that, in addition to its previously shown beneficial effect on NS-linked cardiac and craniofacial defects, RAS/ERK1/2 modulation could also alleviate the short stature phenotype in NS caused by
PTPN11
mutations.
Microbial biopesticides: opportunities and challenges.
Authors: Opender Koul Opender Koul
Published: March 2012

Pesticides based on microorganisms and their products have proven to be highly effective, species specific and eco-friendly in nature, leading to their adoption in pest management strategies around the world. The microbial biopesticide market constitutes about 90% of total biopesticides and there is ample scope for further development in agriculture and public health, although there are challenges as well. This article reviews the various microbial biopesticides that are commercially available, the different approaches for their production and development, the recent technological advances and the challenges faced by the microbial biopesticide field in the future.
Resemblance and investment in children
Authors: Dolinska Barbara
Published: March 2012

According to evolutionary explanations men hardly ever are absolutely certain about their biological fatherhood therefore they must seek various sources of information to subjectively establish whether they are the genetic fathers of the children they raise. Apicella and Marlowe (2004) showed that fathers who perceived greater similarity between their children and themselves were willing to invest more resources (e.g., time, money, care) in their offspring presumably because the perceived resemblance indicated to the fathers their genetic relatedness with their children. The present study extended the design of Apicella and Marlowe's original study and included both fathers and mothers as participants. Parents were recruited by a female confederate at the airport and at the railway station in Wroclaw (Poland). Multiple regression analyses showed that perceived resemblance predicted parental investment in the child for both men and women. The fact that mothers' declarations of investment in their children also depended on the perceived resemblance factor is not consistent with evolutionary formulations delineated by Apicella and Marlowe (2004; 2007). Future studies must resolve the issue of whether the resemblance‐investment relation in fathers results from men relaying on child's resemblance to themselves as an indicator of their own biological paternity, or whether it results from the more parsimonious phenomenon that people in general are attracted more to other people who are similar to them.
How Many Chapters Does the “Yasna of the Seven Chapters” Have?
Authors: Cantera Alberto
Published: February 2012

This article argues that the Avestan text Yasna Haptaŋhāiti (“Yasna of the seven chapters”) was not originally divided into seven chapters. It was divided into three parts that were not considered hāitis (chapters) in the same way as the gathic hāitis. The division of the Yasna Haptaŋhāiti into seven parts and its corresponding title is based on the arrangement of the Old Avestan texts. These texts try to reproduce the structure of the prayer Ahuna Vairiia; three verses with two hemistichs each correspond to three pairs of compositions with 7, 4 four and 1 hāiti each of the Old Avestan texts.
Food, Purity and Pollution: Zoroastrian Views on the Eating Habits of Others
Authors: Daryaee Touraj
Published: February 2012

This article discusses the use of food as a mode of differentiation and identification according to Zoroastrian Middle Persian and Persian texts of the late antique period. In these texts, the list of foods consumed by Arabs and Indians are juxtaposed with that of the Iranian diet, and each group is given anthropological treatment. The article contends that the Zoroastrian dietary law, based on the Middle Persian texts, provides a mode of purity and impurity vis-à-vis others. Finally, the article touches upon the idea of moderation and the consumption of wine as dealt with in some Middle Persian sources.
Characteristics of survivors: growth and nutritional condition of early stages of the hake species Merluccius paradoxus and M. capensis in the southern Benguela ecosystem
Authors: Grote Britta , Ekau Werner , Stenevik Erling K. , Clemmesen Catriona , Verheye Hans M. , Lipinski Marek R. , Hagen Wilhelm
Published: February 2012

Grote, B., Ekau, W., Stenevik, E. K., Clemmesen, C., Verheye, H. M., Lipinski, M. R., and Hagen, W. 2012. Characteristics of survivors: growth and nutritional condition of early stages of the hake species Merluccius paradoxus and M. capensis in the southern Benguela ecosystem. – ICES Journal of Marine Science, 69: 553–562. Larval mortality in marine fish is strongly linked to characteristic traits such as growth and condition, but the variability in these traits is poorly understood. We tried to identify the variability in growth in relation to conditions leading to greater survival chances for early stages of Cape hake, Merluccius paradoxus and M. capensis, in the Benguela upwelling ecosystem. During two cruises in 2007 and one cruise in 2008, hake larvae and juveniles were caught. Otolith microstructures revealed a larval age ranging from 2 to 29 days post-hatching (dph), whereas juvenile age was 67–152 dph. RNA:DNA ratios, used to evaluate nutritional condition, were above the relevant threshold level for growth. No strong coupling between growth and condition was detected, indicating a complex relationship between these factors in the southern Benguela ecosystem. Merluccius paradoxus juveniles caught in 2007 (the surviving larvae of 2006) had significantly higher larval growth rates than larvae hatched in 2007 and 2008, possibly indicating selection for fast growth in 2006. High selection pressure on growth could be linked to predation avoidance, including cannibalism.