bluuebunny/crossref_metadata_2025 huggingface dataset:
Single-hole tunneling through a two-dimensional hole gas in intrinsic silicon
Authors: Spruijtenburg Paul C. , Ridderbos Joost , Mueller Filipp , Leenstra Anne W. , Brauns Matthias , Aarnink Antonius A. I. , van der Wiel Wilfred G. , Zwanenburg Floris A.
Published: May 2013

In this letter we report single-hole tunneling through a quantum dot in a two-dimensional hole gas, situated in a narrow-channel field-effect transistor in intrinsic silicon. Two layers of aluminum gate electrodes are defined on Si/SiO2 using electron-beam lithography. Fabrication and subsequent electrical characterization of different devices yield reproducible results, such as typical MOSFET turn-on and pinch-off characteristics. Additionally, linear transport measurements at 4 K result in regularly spaced Coulomb oscillations, corresponding to single-hole tunneling through individual Coulomb islands. These Coulomb peaks are visible over a broad range in gate voltage, indicating very stable device operation. Energy spectroscopy measurements show closed Coulomb diamonds with single-hole charging energies of 5–10 meV and lines of increased conductance as a result of resonant tunneling through additional available hole states.
Absence of tetragonal distortion in (1−x)SrTiO3-xBi(Zn1/2Ti1/2)O3 solid solution
Authors: Pandey Rishikesh , Kiran Pillutla Ravi , Shankar Uma , Kumar Singh Akhilesh
Published: May 2013

We have carried out powder x-ray diffraction and dielectric studies on the lead free solid solution (1−x)SrTiO3-xBi(Zn1/2Ti1/2)O3 [(1−x)ST-xBZT] with x = 0.05, 0.10, 0.15, 0.20, 0.30, and 0.50 to explore the ferroelectric and piezoelectric properties. Analysis of the powder x-ray diffraction data reveals the cubic structure (space group Pm3m) of (1−x)ST-xBZT for the composition with x ≤ 0.20, at room temperature as well as at low temperature. Highly tetragonal BZT fails to introduce any tetragonality when alloyed with ST. The solid solubility is limited to x < 0.20 and for higher BZT concentrations impurity phases start appearing. The ferroelectric and dielectric characterization of (1−x)ST-xBZT solid solution shows that all the compositions are paraelectric. The implications of the absence of tetragonal distortion in (1−x)ST-xBZT solid solution is discussed in connection with recently investigated other solid solutions based on BZT.
Charge-to-mass-ratio-dependent ion heating during magnetic reconnection in the MST RFP
Authors: Kumar S. T. A. , Almagri A. F. , Craig D. , Den Hartog D. J. , Nornberg M. D. , Sarff J. S. , Terry P. W.
Published: May 2013

Temperature evolution during magnetic reconnection has been spectroscopically measured for various ion species in a toroidal magnetized plasma. Measurements are made predominantly in the direction parallel to the equilibrium magnetic field. It is found that the increase in parallel ion temperature during magnetic reconnection events increases with the charge-to-mass ratio of the ion species. This trend can be understood if the heating mechanism is anisotropic, favoring heating in the perpendicular degree of freedom, with collisional relaxation of multiple ion species. The charge-to-mass ratio trend for the parallel temperature derives from collisional isotropization. This result emphasizes that collisional isotropization and energy transfer must be carefully modeled when analyzing ion heating measurements and comparing to theoretical predictions.
Strain-engineered orthorhombic-rhombohedral phase boundary in epitaxial bismuth ferrite films
Authors: Liu Y. Y. , Yang L. , Li J. Y.
Published: May 2013

Strain-engineered phase boundaries in epitaxial bismuth ferrite films has been investigated via thermodynamics analysis in good agreement with both experimental and first principle studies, and a novel orthorhombic-rhombohedral (OR) phase boundary is found to exist under tensile misfit strain. In contrast to more widely studied tetragonal-rhombohedral phase boundary in bismuth ferrite where enhanced piezoelectric response is largely attributed to extrinsic mechanism, the OR phase boundary is found to show enhanced intrinsic piezoelectric response, and the change of the polarization slope at phase boundary is found to be the key to the enhancement. Difference between strain-engineered phase boundaries and classical morphotropic phase boundary in lead zirconate titanate is also noticed.
Controlling the optical scattering of plasmonic nanoparticles using a thin dielectric layer
Authors: Powell A. W. , Wincott M. B. , Watt A. A. R. , Assender H. E. , Smith J. M.
Published: May 2013

The effect of a thin dielectric film on the plasmonic behaviour of metal nanoparticles (MNPs) above a high refractive index substrate is explored. Using finite-difference time domain simulations, the optical properties of Ag nanoparticles are investigated as a function of film thickness, refractive index, and particle position within the film. We demonstrate that the addition of a film around a MNP at the air interface of a high-index substrate, where nair<nfilm<nsubstrate, will always increase the fraction of light coupled to the substrate (Fsubs). It is found that placement within a layer that does not conform to nair<nfilm<nsubstrate can lead to reduced enhancements in Fsubs. The principal application for this work is for light-trapping in thin-film solar cells. We show that the inclusion of a thin film can increase the fraction of radiation coupled into the substrate by up to 30% for solar wavelengths. Additional potential benefits of the film structure, such as greater tunability of scattering resonances, an increase in path length of light in the substrate, and some control over the emission pattern are demonstrated. MNPs in a film are found to produce a more finely structured emission pattern than particles at a simple interface, showing potential for this research to be applied to optical nanoantennae.
Superconductivity induced by Se-doping in layered charge-density-wave system 1T-TaS2−xSex
Authors: Liu Y. , Ang R. , Lu W. J. , Song W. H. , Li L. J. , Sun Y. P.
Published: May 2013

Layered 1T-TaS2–xSex (0≤x≤2) single crystals have been systematically fabricated by a chemical vapor transport technique. Surprisingly, the superconductivity is induced by the Se doping. We demonstrate the appearance of a series of electronic states: the Mott phase melts into a nearly commensurate charge-density-wave (CDW) phase, superconductivity in a wide x range develops within the nearly commensurate CDW state, and finally commensurate CDW phase reproduces for heavy Se content. The rich phase diagram provides an ideal platform to investigate the interplay between electron correlation, CDW, and superconductivity, as well as the potential applications in electronic devices.
Strong quantum-confined Stark effect from light hole related direct-gap transitions in Ge quantum wells
Authors: Chaisakul P. , Marris-Morini D. , Rouifed M. S. , Frigerio J. , Isella G. , Chrastina D. , Coudevylle J.-R. , Le Roux X. , Edmond S. , Bouville D. , Vivien L.
Published: May 2013

A strong quantum-confined Stark effect (QCSE) from light hole related transitions at the Γ point (LH1-cΓ1) in Ge/Si0.15Ge0.85 multiple quantum wells is demonstrated from both photocurrent and optical transmission measurements. Our experimental results show a large and sharp optical absorption peak due to LH1-cΓ1 transitions, and its associated strong absorption change based on the QCSE. By exploiting LH1-cΓ1 transitions, optical modulators with improved compactness and competitive extinction ratio and optical loss can be envisioned for low energy chip-scale optical interconnect applications.
Probing embedded structural inhomogeneities in MgZnO alloys via selective resonant Raman scattering
Authors: Thapa Dinesh , Huso Jesse , Che Hui , Huso Michelle , Morrison John L. , Gutierrez Diana , Grant Norton M. , Bergman Leah
Published: May 2013

The issue of phase segregation, inherent to the MgZnO alloy system, was investigated via selective resonant Raman scattering. We demonstrate that it is a highly sensitive technique for the detection of embedded structural inhomogeneities. MgZnO thin-films with bandgaps that span the UV-range of 3.2–5.7 eV were realized. Under resonant conditions facilitated via different laser excitation energies, the LO-phonon behavior indicated that the phase segregation is in the range of 35%–65% Mg, in which domains of hexagonal-wurtzite and cubic-NaCl structures coexist. The scattering of the forbidden LO-mode of the cubic phase is discussed in terms of inversion-symmetry relaxation due to alloying.
Perfect surface crystallization and parasitic structures in nonstoichiometric glass-ceramics: Micro-/nanoscopic aspects
Authors: Takahashi Yoshihiro , Yamazaki Yoshiki , Ihara Rie , Fujiwara Takumi
Published: May 2013

Uniform and highly oriented crystalline layers with submillimeter thickness have been demonstrated recently by crystallization in nonstoichiometric precursor glass, i.e., perfectly surface-crystallized glass-ceramics (PSC-GCs). Although the origin of PSC in the SrO−TiO2−SiO2 system was interpreted by the presence of SiO2-rich amorphous nanoparasites on the crystalline domains [Takahashi et al., Sci. Rep. 3, 1147 (2013)], an essential question arose: Is the parasitic structure in PSC-GCs special or natural? To answer it, we prepared PSC samples from other ternary titanosilicate systems and conducted micro- and nanoscopic observations. We found the conditions necessary for PSC by combining our results with previous PSC studies.
Micro-alloying and the toughness of glasses: Modeling with pinned particles
Authors: Dasgupta Ratul , Mishra Pankaj , Procaccia Itamar , Samwer Konrad
Published: May 2013

The usefulness of glasses, and particularly of metallic glasses, in technological applications is often limited by their toughness, (which is defined as the area under the stress vs. strain curve before plastic yielding). Recently, toughness was found to increase significantly by the addition of small concentrations of foreign atoms that act as pinning centers. We model this phenomenon at zero temperature and quasi-static straining with randomly positioned particles that participate in the elastic deformation, but are pinned in the non-affine return to mechanical equilibrium. We find a very strong effect on toughness via the increase of both the shear modulus and the yield stress as a function of the density of pinned particles. Understanding the results calls for analyzing separately the elastic, or “Born term”, and the contributions of the “excess modes” that result from glassy disorder. Finally, we present a scaling theory that collapses the data on one universal curve as a function of rescaled variables.
Fabrication of two-dimensional InGaN/GaN photonic crystal structure using a modified nanosphere lithography technique
Authors: Athanasiou M. , Kim T. K. , Liu B. , Smith R. , Wang T.
Published: May 2013

By means of combining a very cost-effective lift-off process and a nanosphere lithography technique, we have fabricated two dimensional (2D) photonic crystal (PhC) structures on an InGaN/GaN multiple quantum well structure. Significant enhancement in photoluminescence (PL) intensity has been observed when the emission wavelength is within the photonic bandgap. Time-resolved PL measurements have shown that the spontaneous emission rate is strongly reduced by a factor of ∼4 due to the PhC effect. As a consequence, the emission intensity along 2D PhC slab-plane directions is effectively suppressed and redistributed to the direction normal to the 2D PhC slab-plane simultaneously. Temperature-dependent PL measurements have confirmed that the enhanced PL intensity is due to an increase in extraction efficiency as a result of the PhC effect.
Intrinsic and extrinsic origins of low-frequency noise in GaAs/AlGaAs Schottky-gated nanostructures
Authors: Hitachi Kenichi , Ota Takeshi , Muraki Koji
Published: May 2013

We study low-frequency noise in current passing through quantum point contacts fabricated from several GaAs/AlGaAs heterostructures with different layer structures and fabrication processes. In contrast to previous reports, there is no gate-dependent random telegraph noise (RTN) originating from tunneling through a Schottky barrier in devices fabricated using the standard low-damage process. Gate-dependent RTN appears only in devices fabricated with a high-damage process that induces charge trap sites. We show that the insertion of AlAs/GaAs superlattices in the AlGaAs barrier helps to suppress trap formation. Our results enable the fabrication of damage-resistant and thus low-noise devices.
Resonant mode behavior of lumped-resistor-loaded electric-inductive-capacitive resonator and its absorber application
Authors: Lee Hong-Min , Lee Hyung-Sup
Published: May 2013

This paper presents investigations into the resonant mode behavior of a lumped-resistor-loaded electric-inductive-capacitive (ELC) resonator, which is illuminated with a parallel polarization external electromagnetic wave. An ELC resonator exhibits a negative effective permittivity for both parallel and perpendicular polarizations. In contrast to a common ELC resonator, the lumped-resistor-loaded ELC resonator exhibits a switchable resonant mode behavior, thereby revealing a negative effective permeability. In addition, this resonator exhibits a low quality factor owing to the loaded lumped resistors. A metamaterial absorber, which consists of a lumped-resistor-loaded ELC resonator and a cut-wire strip, is designed to confirm the effectiveness of the resonator.
Near-ultraviolet Incoherent Broadband Cavity Enhanced Absorption Spectroscopy for OClO and CH2O in Cl-initiated Photooxidation Experiment
Authors: Dong Mei-li , Zhao Wei-xiong , Huang Ming-qiang , Chen Wei-dong , Hu Chang-jin , Gu Xue-jun , Pei Shi-xin , Huang Wei , Zhang Wei-jun
Published: May 2013

Chlorine dioxide (OClO) is an important indicator for Cl-activation. The monitoring of OClO appears to be crucial for understanding the chemistry of Cl-initialed oxidation and its impact on air quality in polluted coastal regions and industrialized areas. We report the development of a Xe arc lamp based near-ultraviolet (335–375 nm) incoherent broadband cavity enhanced absorption spectroscopy (IBBCEAS) spectrometer for quantitative assessment of OClO in an atmospheric simulation chamber. The important intermediate compound CH2O, and other key atmospheric trace species (NO2) were also simultaneously measured. The instrumental performance shows a strong potential of this kind of IBBCEAS instrument for field and laboratory studies of atmospheric halogen chemistry.
Laser-induced Fluorescence Spectroscopy of NiS: Identification of a Low-lying Electronic State
Authors: Qin Cheng-bing , Zang Jian-zheng , Zhang De-ping , Zhang Qun , Chen Yang
Published: May 2013

Laser-induced fluorescence excitation spectra of jet-cooled NiS molecules were recorded in the energy range of 12200–13550 cm−1. Four vibronic bands with rotational structure have been observed and assigned to the [12.4]3∑0−-X3∑0− transition progression. The relevant rotational constants, significant isotopic shifts, and (equilibrium) molecular parameters have been determined. In addition, the lifetimes of the observed bands have also been measured.
Inversion Vibrational Energy Levels of PH3+(X̃2A2″) Calculated by a New Two-dimension Variational Method
Authors: Dai Zu-yang , Mo Yu-xiang
Published: May 2013

A new 2-D variational method is proposed to calculate the vibrational energy levels of the symmetric P-H stretching vibration (υ1) and the symmetric umbrella vibration (inversion vibration) (υ2) of PH3+(X̃2A2″) that has the tunneling effect. Because the symmetric internal Cartesian coordinates were employed in the calculations, the kinetic energy operator is very simple and the inversion vibrational mode is well characterized. In comparison with the often used 1-D model to calculate the inversion vibrational energy levels, this 2-D method does not require an assumption of reduced mass, and the interactions between the υ1 and υ2 vibrational modes are taken into consideration. The calculated vibrational energy levels of PH3+ are the first reported 2-D calculation, and the average deviation to the experimental data is less than 3 cm−1 for the first seven inversion vibrational energy levels. This method has also been applied to calculate the vibrational energy levels of NH3. The application to NH3 is less successful, which shows some limitations of the method compared with a full dimension computation.
Structural Transition and Magnetic Property of Bi1−xYbxFeO3
Authors: Zheng Ya-nan , Wu Yu-jie , Qin Zhen-xing , Chen Xiao-jia
Published: May 2013

Bi 1−x Yb x FeO 3 (0≤ x ≤0.2 ) powders have been synthesized using a sol-gel method. The X-ray diffraction data show a structural transition from the rhombohedral R3c phase to the orthorhombic Pnma phase between x=0.1 and 0.125, which should induce a ferroelectric-paraelectric transformation. The phase transition is also proven by the Raman spectroscopy. A moderate signal on magnetization appears to illustrate the enhancement of magnetization at the transformation boundary, which is suggested to be the destruction of the spin cycloid structure at low concentration. The appearance of antiferromagnetic ordering is proposed to account for the afterward reduction of the magnetization at high concentration.
Time-dependent Diffusion Coefficient and Conventional Diffusion Constant of Nanoparticles in Polymer Melts by Mode-coupling Theory
Authors: Lai Xin-yu , Zhao Nan-rong
Published: May 2013

Time-dependent diffusion coefficient and conventional diffusion constant are calculated and analyzed to study diffusion of nanoparticles in polymer melts. A generalized Langevin equation is adopted to describe the diffusion dynamics. Mode-coupling theory is employed to calculate the memory kernel of friction. For simplicity, only microscopic terms arising from binary collision and coupling to the solvent density fluctuation are included in the formalism. The equilibrium structural information functions of the polymer nanocomposites required by mode-coupling theory are calculated on the basis of polymer reference interaction site model with Percus-Yevick closure. The effect of nanoparticle size and that of the polymer size are clarified explicitly. The structural functions, the friction kernel, as well as the diffusion coefficient show a rich variety with varying nanoparticle radius and polymer chain length. We find that for small nanoparticles or short chain polymers, the characteristic short time non-Markov diffusion dynamics becomes more prominent, and the diffusion coefficient takes longer time to approach asymptotically the conventional diffusion constant. This constant due to the microscopic contributions will decrease with the increase of nanoparticle size, while increase with polymer size. Furthermore, our result of diffusion constant from mode-coupling theory is compared with the value predicted from the Stokes-Einstein relation. It shows that the microscopic contributions to the diffusion constant are dominant for small nanoparticles or long chain polymers. Inversely, when nanonparticle is big, or polymer chain is short, the hydrodynamic contribution might play a significant role.
Formation and Characteristics of Acrylonitrile/Urea Inclusion Compound
Authors: Zou Jun-ting , Wang Yu-song , Pang Wen-min , Shi Lei , Lu Fei
Published: May 2013

The formation process and composition of the acrylonitrile/urea inclusion compounds (AN/UIC) with different aging times and AN/urea molar feed ratios are studied by differential scanning calorimetry (DSC) and X-ray diffraction (XRD). It is suggested that DSC can determine the guest/host ratio and the heat of decomposition. Meanwhile, the guest/host ratio and heat of decomposition are obtained, which are 1.17 and 5361.53 J/mol, respectively. It is suggested AN molecules included in urea canal lattice may be packed flat against each other. It is found that the formation of AN/UIC depends on the aging time. XRD results reveal that once AN molecules enter urea lattice, AN/UIC are formed, which possess the final structure. When AN molecules are sufficient, the length of AN molecular arrays in urea canals increases as aging time prolonging until urea tunnels are saturated by AN.
Reactive Molecular Dynamics Simulation on Thermal Decomposition of n-Heptane
Authors: Li Juan-qin , Wang Fan , Cheng Xue-ming , Li Xiang-yuan
Published: May 2013

The thermal decomposition of n-heptane is an important process in petroleum industry. The theoretical investigations show that the main products are C2H4, H2, and C3H6, which agree well with the experimental results. The products populations depend strongly on the temperature. The quantity of ethylene increases quickly as the temperature goes up. The conversion of n-heptane and the mole fraction of primary products from reactive molecular dynamic and chemical kinetic modeling are compared with each other. We also investigated the pre-exponential factor and activation energy for thermal decomposition of n-heptane by kinetic analysis from the reactive force field simulations, which were extracted to be 1.78×1014s−1 and 47.32 kcal/mol respectively.
Electrochemical Characterisation of Poly(aniline-co-N-methylaniline) and Poly(aniline-co-N-ethylaniline) Films on Pencil Graphite Electrode for Supercapacitor Applications
Authors: Arslan Andac , Hur Evrim
Published: May 2013

In this work, poly(aniline-co-N-methylaniline) (co-PNMA) and poly(aniline-co-N-ethylaniline) (co-PNEA) have been electrochemically synthesised on pencil graphite electrode (PGE) surface to use as an electrode material for supercapacitors. The films have been formed from aqueous solution of monomers and sulfuric acid as electrolyte. The copolymer films have been characterised by cyclic voltammetry (CV), Mott-Schottky (MS) analysis, and scanning electron microscopy (SEM). The electrochemical storage properties of uncoated electrode and copolymer coated electrodes (PGE/co-PNMA and PGE/co-PNEA) have been investigated via CV, electrochemical impedance spectroscopy (EIS), and repeating chronopotentiometry (RCP) methods in 0.100 M H2SO4 solution. Experimental results indicate that PGE/co-PNMA exhibits higher specific capacitance than PGE/co-PNEA. Highest specific capacitance values of the PGE/co-PNMA and PGE/co-PNEA have been obtained as 213.85 mF g–1 (17.7 mF cm–2) and 48.60 mF g–1 (4.36 mF cm–2) at 50 mV s–1, respectively when compared with that of uncoated PGE which is 1.63 mF g–1 (0.14 mF cm–2). Charge-discharge characteristics of the electrodes have shown that both of the electrodes can be used as supercapacitor electrode active materials for low voltage (<10 V) applications.
Scope for improved eco-efficiency varies among diverse cropping systems
Authors: Carberry Peter S. , Liang Wei-li , Twomlow Stephen , Holzworth Dean P. , Dimes John P. , McClelland Tim , Huth Neil I. , Chen Fu , Hochman Zvi , Keating Brian A.
Published: May 2013

Global food security requires eco-efficient agriculture to produce the required food and fiber products concomitant with ecologically efficient use of resources. This eco-efficiency concept is used to diagnose the state of agricultural production in China (irrigated wheat–maize double-cropping systems), Zimbabwe (rainfed maize systems), and Australia (rainfed wheat systems). More than 3,000 surveyed crop yields in these three countries were compared against simulated grain yields at farmer-specified levels of nitrogen (N) input. Many Australian commercial wheat farmers are both close to existing production frontiers and gain little prospective return from increasing their N input. Significant losses of N from their systems, either as nitrous oxide emissions or as nitrate leached from the soil profile, are infrequent and at low intensities relative to their level of grain production. These Australian farmers operate close to eco-efficient frontiers in regard to N, and so innovations in technologies and practices are essential to increasing their production without added economic or environmental risks. In contrast, many Chinese farmers can reduce N input without sacrificing production through more efficient use of their fertilizer input. In fact, there are real prospects for the double-cropping systems on the North China Plain to achieve both production increases and reduced environmental risks. Zimbabwean farmers have the opportunity for significant production increases by both improving their technical efficiency and increasing their level of input; however, doing so will require improved management expertise and greater access to institutional support for addressing the higher risks. This paper shows that pathways for achieving improved eco-efficiency will differ among diverse cropping systems.
New technologies reduce greenhouse gas emissions from nitrogenous fertilizer in China
Authors: Zhang Wei-feng , Dou Zheng-xia , He Pan , Ju Xiao-Tang , Powlson David , Chadwick Dave , Norse David , Lu Yue-Lai , Zhang Ying , Wu Liang , Chen Xin-Ping , Cassman Kenneth G. , Zhang Fu-Suo
Published: May 2013

Synthetic nitrogen (N) fertilizer has played a key role in enhancing food production and keeping half of the world’s population adequately fed. However, decades of N fertilizer overuse in many parts of the world have contributed to soil, water, and air pollution; reducing excessive N losses and emissions is a central environmental challenge in the 21st century. China’s participation is essential to global efforts in reducing N-related greenhouse gas (GHG) emissions because China is the largest producer and consumer of fertilizer N. To evaluate the impact of China’s use of N fertilizer, we quantify the carbon footprint of China’s N fertilizer production and consumption chain using life cycle analysis. For every ton of N fertilizer manufactured and used, 13.5 tons of CO2-equivalent (eq) (t CO2-eq) is emitted, compared with 9.7 t CO2-eq in Europe. Emissions in China tripled from 1980 [131 terrogram (Tg) of CO2-eq (Tg CO2-eq)] to 2010 (452 Tg CO2-eq). N fertilizer-related emissions constitute about 7% of GHG emissions from the entire Chinese economy and exceed soil carbon gain resulting from N fertilizer use by several-fold. We identified potential emission reductions by comparing prevailing technologies and management practices in China with more advanced options worldwide. Mitigation opportunities include improving methane recovery during coal mining, enhancing energy efficiency in fertilizer manufacture, and minimizing N overuse in field-level crop production. We find that use of advanced technologies could cut N fertilizer-related emissions by 20–63%, amounting to 102–357 Tg CO2-eq annually. Such reduction would decrease China’s total GHG emissions by 2–6%, which is significant on a global scale.
Dynamic dual-tracer MRI-guided fluorescence tomography to quantify receptor density in vivo
Authors: Davis Scott C. , Samkoe Kimberley S. , Tichauer Kenneth M. , Sexton Kristian J. , Gunn Jason R. , Deharvengt Sophie J. , Hasan Tayyaba , Pogue Brian W.
Published: May 2013

The up-regulation of cell surface receptors has become a central focus in personalized cancer treatment; however, because of the complex nature of contrast agent pharmacokinetics in tumor tissue, methods to quantify receptor binding in vivo remain elusive. Here, we present a dual-tracer optical technique for noninvasive estimation of specific receptor binding in cancer. A multispectral MRI-coupled fluorescence molecular tomography system was used to image the uptake kinetics of two fluorescent tracers injected simultaneously, one tracer targeted to the receptor of interest and the other tracer a nontargeted reference. These dynamic tracer data were then fit to a dual-tracer compartmental model to estimate the density of receptors available for binding in the tissue. Applying this approach to mice with deep-seated gliomas that overexpress the EGF receptor produced an estimate of available receptor density of 2.3 ± 0.5 nM (
n
= 5), consistent with values estimated in comparative invasive imaging and ex vivo studies.
Multiple actions of φ-LITX-Lw1a on ryanodine receptors reveal a functional link between scorpion DDH and ICK toxins
Authors: Smith Jennifer J. , Vetter Irina , Lewis Richard J. , Peigneur Steve , Tytgat Jan , Lam Alexander , Gallant Esther M. , Beard Nicole A. , Alewood Paul F. , Dulhunty Angela F.
Published: May 2013

We recently reported the isolation of a scorpion toxin named U
1
-liotoxin-Lw1a (U
1
-LITX-Lw1a) that adopts an unusual 3D fold termed the disulfide-directed hairpin (DDH) motif, which is the proposed evolutionary structural precursor of the three-disulfide-containing inhibitor cystine knot (ICK) motif found widely in animals and plants. Here we reveal that U
1
-LITX-Lw1a targets and activates the mammalian ryanodine receptor intracellular calcium release channel (RyR) with high (fM) potency and provides a functional link between DDH and ICK scorpion toxins. Moreover, U
1
-LITX-Lw1a, now described as φ-liotoxin-Lw1a (φ-LITX-Lw1a), has a similar mode of action on RyRs as scorpion calcines, although with significantly greater potency, inducing full channel openings at lower (fM) toxin concentrations whereas at higher pM concentrations increasing the frequency and duration of channel openings to a submaximal state. In addition, we show that the C-terminal residue of φ-LITX-Lw1a is crucial for the increase in full receptor openings but not for the increase in receptor subconductance opening, thereby supporting the two-binding-site hypothesis of scorpion toxins on RyRs. φ-LITX-Lw1a has potential both as a pharmacological tool and as a lead molecule for the treatment of human diseases that involve RyRs, such as malignant hyperthermia and polymorphic ventricular tachycardia.
Ultrafast real-time visualization of active site flexibility of flavoenzyme thymidylate synthase ThyX
Authors: Laptenok Sergey P. , Bouzhir-Sima Latifa , Lambry Jean-Christophe , Myllykallio Hannu , Liebl Ursula , Vos Marten H.
Published: May 2013

In many bacteria the flavoenzyme thymidylate synthase ThyX produces the DNA nucleotide deoxythymidine monophosphate from dUMP, using methylenetetrahydrofolate as carbon donor and NADPH as hydride donor. Because all three substrates bind in close proximity to the catalytic flavin adenine dinucleotide group, substantial flexibility of the ThyX active site has been hypothesized. Using femtosecond time-resolved fluorescence spectroscopy, we have studied the conformational heterogeneity and the conformational interconversion dynamics in real time in ThyX from the hyperthermophilic bacterium
Thermotoga maritima
. The dynamics of electron transfer to excited flavin adenine dinucleotide from a neighboring tyrosine residue are used as a sensitive probe of the functional dynamics of the active site. The fluorescence decay spanned a full three orders of magnitude, demonstrating a very wide range of conformations. In particular, at physiological temperatures, multiple angstrom cofactor-residue displacements occur on the picoseconds timescale. These experimental findings are supported by molecular dynamics simulations. Binding of the dUMP substrate abolishes this flexibility and stabilizes the active site in a configuration where dUMP closely interacts with the flavin cofactor and very efficiently quenches fluorescence itself. Our results indicate a dynamic selected-fit mechanism where binding of the first substrate dUMP at high temperature stabilizes the enzyme in a configuration favorable for interaction with the second substrate NADPH, and more generally have important implications for the role of active site flexibility in enzymes interacting with multiple poly-atom substrates and products. Moreover, our data provide the basis for exploring the effect of inhibitor molecules on the active site dynamics of ThyX and other multisubstrate flavoenzymes.
PI3Kα activates integrin α4β1 to establish a metastatic niche in lymph nodes
Authors: Garmy-Susini Barbara , Avraamides Christie J. , Desgrosellier Jay S. , Schmid Michael C. , Foubert Philippe , Ellies Lesley G. , Lowy Andrew M. , Blair Sarah L. , Vandenberg Scott R. , Datnow Brian , Wang Huan-You , Cheresh David A. , Varner Judith
Published: May 2013

Lymph nodes are initial sites of tumor metastasis, yet whether the lymph node microenvironment actively promotes tumor metastasis remains unknown. We show here that VEGF-C/PI3Kα-driven remodeling of lymph nodes promotes tumor metastasis by activating integrin α4β1 on lymph node lymphatic endothelium. Activated integrin α4β1 promotes expansion of the lymphatic endothelium in lymph nodes and serves as an adhesive ligand that captures vascular cell adhesion molecule 1 (VCAM-1)
+
metastatic tumor cells, thereby promoting lymph node metastasis. Experimental induction of α4β1 expression in lymph nodes is sufficient to promote tumor cell adhesion to lymphatic endothelium and lymph node metastasis in vivo, whereas genetic or pharmacological blockade of integrin α4β1 or VCAM-1 inhibits it. As lymph node metastases accurately predict poor disease outcome, and integrin α4β1 is a biomarker of lymphatic endothelium in tumor-draining lymph nodes from animals and patients, these results indicate that targeting integrin α4β1 or VCAM to inhibit the interactions of tumor cells with the lymph node microenvironment may be an effective strategy to suppress tumor metastasis.
Dynamic CREB family activity drives segmentation and posterior polarity specification in mammalian somitogenesis
Authors: Lopez T. Peter , Fan Chen-Ming
Published: May 2013

Significance

The segmented axial skeleton of vertebrates is composed of an interlinked framework of vertebrae and ribs. During embryogenesis, vertebral precursors known as somites form sequentially from a progenitor tissue known as the presomitic mesoderm to foreshadow the metamerism of the axial skeleton. We have discovered that the cAMP responsive element binding protein (CREB) family of transcription factors operates in combination with Notch and Wnt signaling to instruct the timely scission of presomitic mesoderm into somites with proper anterior/posterior polarities. Thus, the CREB family represents a new and important molecular integrator in axial skeleton development. Our work has potential implications to spinal disorders such as scoliosis.
Millennial-scale isotope records from a wide-ranging predator show evidence of recent human impact to oceanic food webs
Authors: Wiley Anne E. , Ostrom Peggy H. , Welch Andreanna J. , Fleischer Robert C. , Gandhi Hasand , Southon John R. , Stafford Thomas W. , Penniman Jay F. , Hu Darcy , Duvall Fern P. , James Helen F.
Published: May 2013

Human exploitation of marine ecosystems is more recent in oceanic than near shore regions, yet our understanding of human impacts on oceanic food webs is comparatively poor. Few records of species that live beyond the continental shelves date back more than 60 y, and the sheer size of oceanic regions makes their food webs difficult to study, even in modern times. Here, we use stable carbon and nitrogen isotopes to study the foraging history of a generalist, oceanic predator, the Hawaiian petrel (
Pterodroma sandwichensis
), which ranges broadly in the Pacific from the equator to near the Aleutian Islands. Our isotope records from modern and ancient, radiocarbon-dated bones provide evidence of over 3,000 y of dietary stasis followed by a decline of ca. 1.8‰ in δ
15
N over the past 100 y. Fishery-induced trophic decline is the most likely explanation for this sudden shift, which occurs in genetically distinct populations with disparate foraging locations. Our isotope records also show that coincident with the apparent decline in trophic level, foraging segregation among petrel populations decreased markedly. Because variation in the diet of generalist predators can reflect changing availability of their prey, a foraging shift in wide-ranging Hawaiian petrel populations suggests a relatively rapid change in the composition of oceanic food webs in the Northeast Pacific. Understanding and mitigating widespread shifts in prey availability may be a critical step in the conservation of endangered marine predators such as the Hawaiian petrel.
Essential role for Cdk2 inhibitory phosphorylation during replication stress revealed by a human Cdk2 knockin mutation
Authors: Hughes Bridget T. , Sidorova Julia , Swanger Jherek , Monnat Raymond J. , Clurman Bruce E.
Published: May 2013

Cyclin-dependent kinases (Cdks) coordinate cell division, and their activities are tightly controlled. Phosphorylation of threonine 14 (T14) and tyrosine 15 (Y15) inhibits Cdks and regulates their activities in numerous physiologic contexts. Although the roles of Cdk1 inhibitory phosphorylation during mitosis are well described, studies of Cdk2 inhibitory phosphorylation during S phrase have largely been indirect. To specifically study the functions of Cdk2 inhibitory phosphorylation, we used gene targeting to make an endogenous Cdk2 knockin allele in human cells, termed Cdk2AF, which prevents Cdk2 T14 and Y15 phosphorylation. Cdk2AF caused premature S-phase entry, rapid cyclin E degradation, abnormal DNA replication, and genome instability. Cdk2AF cells also exhibited strikingly abnormal responses to replication stress, accumulated irreparable DNA damage, and permanently exited the cell cycle after transient exposure to S-phase inhibitors. Our results reveal the specific and essential roles of Cdk2 inhibitory phosphorylation in the successful execution of the replication stress checkpoint response and in maintaining genome integrity.
Calcium signaling mediates cold sensing in insect tissues
Authors: Teets Nicholas M. , Yi Shu-Xia , Lee Richard E. , Denlinger David L.
Published: May 2013

The ability to rapidly respond to changes in temperature is a critical adaptation for insects and other ectotherms living in thermally variable environments. In a process called rapid cold hardening (RCH), insects significantly enhance cold tolerance following brief (i.e., minutes to hours) exposure to nonlethal chilling. Although the ecological relevance of RCH is well-established, the underlying physiological mechanisms that trigger RCH are poorly understood. RCH can be elicited in isolated tissues ex vivo, suggesting cold-sensing and downstream hardening pathways are governed by brain-independent signaling mechanisms. We previously provided preliminary evidence that calcium is involved in RCH, and here we firmly establish that calcium signaling mediates cold sensing in insect tissues. In tracheal cells of the freeze-tolerant goldenrod gall fly,
Eurosta solidaginis,
chilling to 0 °C evoked a 40% increase in intracellular calcium concentration as determined by live-cell confocal imaging. Downstream of calcium entry, RCH conditions significantly increased the activity of calcium/calmodulin-dependent protein kinase II (CaMKII) while reducing phosphorylation of the inhibitory Thr306 residue. Pharmacological inhibitors of calcium entry, calmodulin activation, and CaMKII activity all prevented ex vivo RCH in midgut and salivary gland tissues, indicating that calcium signaling is required for RCH to occur. Similar results were obtained for a freeze-intolerant species, adults of the flesh fly,
Sarcophaga bullata,
suggesting that calcium-mediated cold sensing is a general feature of insects. Our results imply that insect tissues use calcium signaling to instantly detect decreases in temperature and trigger downstream cold-hardening mechanisms.
Molecular layer perforant path-associated cells contribute to feed-forward inhibition in the adult dentate gyrus
Authors: Li Yan , Stam Floor J. , Aimone James B. , Goulding Martyn , Callaway Edward M. , Gage Fred H.
Published: May 2013

New neurons, which have been implicated in pattern separation, are continually generated in the dentate gyrus in the adult hippocampus. Using a genetically modified rabies virus, we demonstrated that molecular layer perforant pathway (MOPP) cells innervated newborn granule neurons in adult mouse brain. Stimulating the perforant pathway resulted in the activation of MOPP cells before the activation of dentate granule neurons. Moreover, activation of MOPP cells by focal uncaging of glutamate induced strong inhibition of granule cells. Together, these results indicate that MOPP cells located in the molecular layer of the dentate gyrus contribute to feed-forward inhibition of granule cells via perforant pathway activation.
Concordant mast cell and basophil production by individual hematopoietic blast colony-forming cells
Authors: Metcalf Donald , Ng Ashley P. , Baldwin Tracey M. , Di Rago Ladina , Mifsud Sandra
Published: May 2013

Previous studies have shown that mouse bone marrow cells can produce mast cells when stimulated in vitro by stem cell factor (SCF) and interleukin-3 (IL-3). Experiments to define the marrow cells able to generate mast cells showed that the most active subpopulations were the Kit+Sca1–progenitor cell fraction and the more ancestral Kit+Sca1+blast colony-forming cell fraction. In clonal cultures, up to 64% of blast colony-forming cells were able to generate mast cells when stimulated by SCF and IL-3, and, of these, the most active were those in the CD34–Flt3R–long-term repopulating cell fraction. Basophils, identified by the monoclonal antibody mMCP-8 to mouse mast cell serine protease-8, were also produced by 50% of blast colony-forming cells with a strong concordance in the production of both cell types by individual blast colony-forming cells. Enriched populations of marrow-derived basophils were shown to generate variable numbers of mast cells after a further incubation with SCF and IL-3. The data extend the repertoire of lineage-committed cells able to be produced by multipotential hematopoietic blast colony-forming cells and show that basophils and mast cells can have common ancestral cells and that basophils can probably generate mast cells at least under defined in vitro conditions.
Narration of Violence or Violence of Narration: Bahram Beyzaie's The Eighth Voyage of Sinbad and The One Thousand and First Night
Authors: Samini Naghmeh
Published: May 2013

Bahram Beyzaie is one of the most distinguished Iranian playwrights. Beginning his career in the early 1960s and still working, he is considered as a playwright who has always been looking for discovering and inventing non-classic and non-western narrative templates. To fulfill this purpose, he has made considerable use of classic Iranian literary sources, among which the One Thousand and One Nights and Ta'ziyeh texts are special cases. By analyzing Beyzaie's two plays, Hashtomin Safar-e Sandbad (The Eighth Voyage of Sinbad, 1964) and Shab-e Hezar-o Yekom (The One Thousand and First Night, 2003), which were produced within a forty-year period, this article attempts to highlight some of Beyzaie's methods of narration, particularly in relation to violence.
Inactivation of the RB family prevents thymus involution and promotes thymic function by direct control of Foxn1 expression
Authors: Garfin Phillip M. , Min Dullei , Bryson Jerrod L. , Serwold Thomas , Edris Badreddin , Blackburn Clare C. , Richie Ellen R. , Weinberg Kenneth I. , Manley Nancy R. , Sage Julien , Viatour Patrick
Published: May 2013

Thymic involution during aging is a major cause of decreased production of T cells and reduced immunity. Here we show that inactivation of Rb family genes in young mice prevents thymic involution and results in an enlarged thymus competent for increased production of naive T cells. This phenotype originates from the expansion of functional thymic epithelial cells (TECs). In RB family mutant TECs, increased activity of E2F transcription factors drives increased expression of Foxn1, a central regulator of the thymic epithelium. Increased Foxn1 expression is required for the thymic expansion observed in Rb family mutant mice. Thus, the RB family promotes thymic involution and controls T cell production via a bone marrow–independent mechanism, identifying a novel pathway to target to increase thymic function in patients.
Evaluating the Trade Restrictiveness of Phytosanitary Measures on U.S. Fresh Fruit and Vegetable Imports
Authors: Peterson Everett , Grant Jason , Roberts Donna , Karov Vuko
Published: May 2013

Empirically assessing sanitary and phytosanitary regulations has proven difficult because most data sources indicate whether a regulation exists but provide no information on the type or importance of the respective measure. In this article, we construct a novel database of U.S. phytosanitary measures and match these to 47 fresh fruit and vegetable product imports from 89 exporting countries over the period 1996–2008. A product‐line gravity equation that accounts for zero trade flows is developed to investigate the trade impact of different pest‐mitigation measures. While the results suggest that phytosanitary treatments generally reduce trade, the actual restrictiveness of these measures diminishes dramatically as exporters accumulate experience, and it vanishes when exporters reach a certain threshold. The results have important policy implications considering the number of empirical studies that find a negative impact of non‐tariff measures on trade.
Dead or alive—estimating post-release mortality of Atlantic cod in the recreational fishery
Authors: Weltersbach Marc Simon , Strehlow Harry V.
Published: May 2013

Weltersbach, M. S., and Strehlow, H. V. 2013. Dead or alive—estimating post-release mortality of Atlantic cod in the recreational fishery. – ICES Journal of Marine Science, 70: 864–872. Atlantic cod (Gadus morhua) is one of the most important commercial and recreational target species in European marine waters. Recent recreational fisheries surveys revealed that recreational cod catches and release rates are substantial compared to the commercial fishery, particularly in the western Baltic Sea. Despite high release rates, no literature exists exploring the post-release mortality of cod and potential sublethal effects after catch-and-release in recreational fisheries. This study investigates (i) the post-release mortality of undersized cod, (ii) potential factors affecting mortality, and (iii) consequences of the catch-and-release process on cod. During four experimental trials, western Baltic Sea cod were angled from a charter vessel and thereafter observed together with control fish in netpens for 10 d at holding temperatures between 6.2 and 19.8°C. Adjusted mortality rates for angled cod ranged from 0.0–27.3% (overall mean 11.2%). A logistic regression analysis revealed that bleeding and holding-water temperature were the only significant predictors of mortality. Slow hook injury healing (>10 d) and bacterial wound infections were observed in some surviving cod. The results will help to increase the accuracy of recreational cod removal estimates and thereby improve the management of western Baltic cod stock.
Towards sustainable fisheries of the Öresund cod (Gadus morhua) through sub-stock-specific assessment and management recommendations
Authors: Lindegren Martin , Waldo Staffan , Nilsson P. Anders , Svedäng Henrik , Persson Anders
Published: May 2013

Lindegren, M., Waldo, S., Nilsson, P. A., Svedäng, H., and Persson, A. 2013. Towards sustainable fisheries of the Öresund cod (Gadus morhua) through sub-stock-specific assessment and management recommendations. – ICES Journal of Marine Science, 70: 1140–1150. Fisheries management traditionally relies on stock assessments assuming discrete populations within large administrational areas. However, failing to account for sub-stock structuring may result in overestimation of the stocks' true harvest potential and unsustainable exploitation of small stock elements. Atlantic cod (Gadus morhua) frequently occurs in spatially segregated populations, some of which exhibit fine-scaled stock structuring within current management boundaries. Here we use the locally spawning cod stock in the Sound (“Öresund”) as a case study, and perform a sub-stock-specific assessment to evaluate biological and economic effects of managing the Sound cod as a separate stock. Our results indicate that reducing exploitation pressure, particularly through technical regulations i.e. increasing gill-net mesh sizes, would not only enhance the stock age distribution, but yield long-term net benefits to the local gill-net fishery. Furthermore, our study emphasizes the need for developing sub-stock-specific management recommendations in order to ensure the maintenance of fisheries resources in general, and the persistence of sub-stock structuring in particular.