bluuebunny/crossref_metadata_2025 huggingface dataset:
Computational IR spectroscopy of water: OH stretch frequencies, transition dipoles, and intermolecular vibrational coupling constants
Authors: Choi Jun-Ho , Cho Minhaeng
Published: May 2013

The Hessian matrix reconstruction method initially developed to extract the basis mode frequencies, vibrational coupling constants, and transition dipoles of the delocalized amide I, II, and III vibrations of polypeptides and proteins from quantum chemistry calculation results is used to obtain those properties of delocalized O–H stretch modes in liquid water. Considering the water symmetric and asymmetric O–H stretch modes as basis modes, we here develop theoretical models relating vibrational frequencies, transition dipoles, and coupling constants of basis modes to local water configuration and solvent electric potential. Molecular dynamics simulation was performed to generate an ensemble of water configurations that was in turn used to construct vibrational Hamiltonian matrices. Obtaining the eigenvalues and eigenvectors of the matrices and using the time-averaging approximation method, which was developed by the Skinner group, to calculating the vibrational spectra of coupled oscillator systems, we could numerically simulate the O–H stretch IR spectrum of liquid water. The asymmetric line shape and weak shoulder bands were quantitatively reproduced by the present computational procedure based on vibrational exciton model, where the polarization effects on basis mode transition dipoles and inter-mode coupling constants were found to be crucial in quantitatively simulating the vibrational spectra of hydrogen-bond networking liquid water.
Three new branched chain equations of state based on Wertheim's perturbation theory
Authors: Marshall Bennett D. , Chapman Walter G.
Published: May 2013

In this work, we present three new branched chain equations of state (EOS) based on Wertheim's perturbation theory. The first represents a slightly approximate general branched chain solution of Wertheim's second order perturbation theory (TPT2) for athermal hard chains, and the second represents the extension of first order perturbation theory with a dimer reference fluid (TPT1-D) to branched athermal hard chain molecules. Each athermal branched chain EOS was shown to give improved results over their linear counterparts when compared to simulation data for branched chain molecules with the branched TPT1-D EOS being the most accurate. Further, it is shown that the branched TPT1-D EOS can be extended to a Lennard–Jones dimer reference system to obtain an equation of state for branched Lennard–Jones chains. The theory is shown to accurately predict the change in phase diagram and vapor pressure which results from branching as compared to experimental data for n-octane and corresponding branched isomers.
Efficiency enhancement of nonlinear odd harmonics in thermal free electron laser
Authors: Bazouband F. , Maraghechi B.
Published: May 2013

The effect of axial energy spread on the radiation of third harmonic is studied in the free electron laser with planar wiggler and ion-channel guiding. Spread in the longitudinal momentum and so in the initial energy of electron beam, without any spread in the transverse velocity, is assumed in the form of Gaussian distribution function. The technique that is employed is a one-dimensional and steady-state simulation. A set of self consistent nonlinear differential equations that describes the system is solved numerically by Runge-Kutta method. Due to the sensitivity of harmonics to thermal effects, gain improvement of third harmonic radiation is achieved by using ion-channel guiding technique and efficiency enhancement is applied by tapering the magnetic field of wiggler to optimize radiation. The bunching parameter of the electron beam is also studied. It is found that the growth of the magnitude of the bunching parameter that is caused by the ponderomotive wave stops before the saturation point of the radiation. This means that ponderomotive wave saturates at a shorter distance compared to the radiation.
Coherent electron transfer in a coupled quantum dot nanostructure using stimulated Raman adiabatic passage
Authors: Fountoulakis Antonios , Paspalakis Emmanuel
Published: May 2013

We study the potential for coherent transfer of a single electron between the ground states of two anharmonic coupled quantum dots using an adiabatic passage method. We consider the interaction of a quantum dot structure characterized by an asymmetric confining potential by two external electromagnetic fields. We use the method of stimulated Raman adiabatic passage (STIRAP) for control of the dynamics of the electron, and ultimately for succeeding the transfer of the electron from the initially occupied quantum dot to the other quantum dot. Results for several values of the parameters of the applied electromagnetic fields are presented, and we show that STIRAP can lead to efficient coherent single electron transfer for a wide range of these parameters.
Large amplitude inertial compressional Alfvénic shock and solitary waves, and acceleration of ions in magnetohydrodynamic plasmas
Authors: Panwar Anuraj , Rizvi H. , Ryu C. M.
Published: May 2013

Large amplitude inertial compressional Alfvénic shock and solitary waves in magnetohydrodynamic plasmas are investigated. Dispersive effect caused by non-ideal electron inertia currents perpendicular to the ambient magnetic field can balance the nonlinear steepening of waves leading to the formation of a soliton. A Sagdeev-potential formalism is employed to derive an energy-balance like equation. The range of allowed values of the soliton speed, M (Mach number), plasma β (ratio of the plasma thermal pressure to the pressure in the confining magnetic field), and electron inertia, wherein solitary waves may exist, are determined. Depth of the potential increases with increasing the Mach number and plasma β, however decreases with the increasing electron inertia. The height of soliton increases with increasing in Mach number and decreases with plasma β. And with increasing electron inertial length, the width of soliton increases. The electron-ion collisional dissipation results a dissipative inertial compressional Alfvén wave, which can produce a shock like structure and can efficiently accelerate ions to the order of the local Alfvén velocity. The shock height increases with the increasing collision frequency, but shock height decreases with increasing plasma β.
Generalized model for ultrafast laser induced electron emission from a metal tip
Authors: Ang L. K. , Pant M.
Published: May 2013

In this paper, we will present a brief review of the recently developed non-equilibrium heating and time dependent tunneling model to study the dynamic processes in using an ultrafast laser to induce electron emission from a metallic tip ranging from the multiphoton to the optical tunneling regime. Due to the short time scale of the ultrafast laser pulse, the lattice is found to be in a non-equilibrium condition and a single temperature model is no longer valid. The ultrafast laser heating enhances the electron emission through both the multiphoton and optical tunneling processes rather than over-barrier emission due to thermal heating. The paper is focused on the methodology of how these two effects (non-equilibrium heating and time-dependent tunneling) are combined in a self-consistent model. The model shows a smooth transition of the emitted charge as a function of laser field, ranging from the multiphoton emission regime at low laser field to the optical tunneling regime at high laser field. The paper will conclude with some discussion of future work.
The structure of liquid GeSe revisited: A first principles molecular dynamics study
Authors: Le Roux Sébastien , Bouzid Assil , Boero Mauro , Massobrio Carlo
Published: May 2013

Early first-principles molecular dynamics results on liquid GeSe were characterized by shortcomings in the description of Ge–Ge (and to a lesser extent Se–Se) short range correlations. In that case the exchange-correlation functional adopted was the one devised by Perdew and Wang (PW91). In the search of improvements in the atomic-scale modelling of this liquid, we have produced new sets of data by employing two different schemes for the exchange-correlation part within the density functional theory approach. The two functionals selected are those proposed by Becke, Lee, Yang, and Parr (BLYP) and by Perdew, Burke, and Ernzerhof (PBE). The PBE results turned out to be quite similar to the PW91 ones. The BLYP results feature instead a better account of the Ge–Ge first shell of neighbors, correctly exhibiting two clear maxima separated by a deep minimum. Due to the increase in the number of the tetrahedral structural units, the atomic mobility of Ge and Se atoms in the network is reduced with respect to the PW91 case. This brings the diffusion coefficients of the two species down to values close to those of liquid Ge2Se3 and liquid GeSe2.
Effect of local metal microstructure on adsorption on bimetallic surfaces: Atomic nitrogen on Ni/Pt(111)
Authors: Guo Wei , Vlachos Dionisios G.
Published: May 2013

The adsorption of atomic nitrogen on Ni/Pt(111) surface bimetallics has been investigated as a function of the local microstructure of Ni and Pt atoms via density functional theory (DFT) calculations. Microstructures include surface and subsurface Ni atoms on Pt(111) as limiting cases, and also small clusters of Ni in the first and/or second layer of Pt. It is shown that the binding energy of N can be approximated as a perturbation from that on the host metal (Pt) with a linear short-ranged correction from the guest metal (Ni) that accounts for the coordination environment of nitrogen up to the 3rd nearest Ni neighbor. This model is rationalized with the d-band center theory. Coverage effects are also included. The model can be parameterized with a limited number of DFT calculations and applied to other bimetallic catalysts to estimate the coverage dependent binding energy on complex metal microstructures.
Analysis of the AlGaN/GaN vertical bulk current on Si, sapphire, and free-standing GaN substrates
Authors: Pérez-Tomás A. , Fontserè A. , Llobet J. , Placidi M. , Rennesson S. , Baron N. , Chenot S. , Moreno J. C. , Cordier Y.
Published: May 2013

The vertical bulk (drain-bulk) current (Idb) properties of analogous AlGaN/GaN hetero-structures molecular beam epitaxially grown on silicon, sapphire, and free-standing GaN (FS-GaN) have been evaluated in this paper. The experimental Idb (25–300 °C) have been well reproduced with physical models based on a combination of Poole-Frenkel (trap assisted) and hopping (resistive) conduction mechanisms. The thermal activation energies (Ea), the (soft or destructive) vertical breakdown voltage (VB), and the effect of inverting the drain-bulk polarity have also been comparatively investigated. GaN-on-FS-GaN appears to adhere to the resistive mechanism (Ea = 0.35 eV at T = 25–300 °C; VB = 840 V), GaN-on-sapphire follows the trap assisted mechanism (Ea = 2.5 eV at T > 265 °C; VB > 1100 V), and the GaN-on-Si is well reproduced with a combination of the two mechanisms (Ea = 0.35 eV at T > 150 °C; VB = 420 V). Finally, the relationship between the vertical bulk current and the lateral AlGaN/GaN transistor leakage current is explored.
Hartman effect and dissipative quantum systems
Authors: Bhattacharya Samyadeb , Roy Sisir
Published: May 2013

The dwell time for dissipative quantum system is shown to increase with barrier width. It clearly precludes Hartman effect for dissipative systems. Here calculation has been done for inverted parabolic potential barrier.
Organic [6,6]-phenyl-C61-butyric-acid-methyl-ester field effect transistors: Analysis of the contact properties by combined photoemission spectroscopy and electrical measurements
Authors: Scheinert S. , Grobosch M. , Sprogies J. , Hörselmann I. , Knupfer M. , Paasch G.
Published: May 2013

Carrier injection barriers determined by photoemission spectroscopy for organic/metal interfaces are widely accepted to determine the performance of organic field-effect transistors (OFET), which strongly depends on this interface at the source/drain contacts. This assumption is checked here in detail, and a more sophisticated connection is presented. According to the preparation process described in our recently published article [S. Scheinert, J. Appl. Phys. 111, 064502 (2012)], we prepared PCBM/Au and PCBM/Al samples to characterize the interface by photoemission and electrical measurements of PCBM based OFETs with bottom and top (TOC) contacts, respectively. The larger drain currents for TOC OFETs indicate the presence of Schottky contacts at source/drain for both metals. The hole injection barrier as determined by photoemission is 1.8 eV for both Al and Au. Therefore, the electron injection barriers are also the same. In contrast, the drain currents are orders of magnitude larger for the transistors with the Al contacts than for those with the Au contacts. We show that indeed the injection is determined by two other properties measured also by photoemission, the (reduced) work functions, and the interface dipoles, which have different sign for each contact material. In addition, we demonstrate by core-level and valence band photoemission that the deposition of gold as top contact onto PCBM results in the growth of small gold clusters. With increasing gold coverage, the clusters grow inside and begin to form a metallic, but not uniform, closed film onto PCBM.
Magnetic field induced dielectric relaxation in the strain glass state of Pr0.6Ca0.4MnO3
Authors: Chandrasekhar K. Devi , Das A. K. , Venimadhav A.
Published: May 2013

We present the dielectric and magnetodielectric properties of Pr0.6Ca0.4MnO3 polycrystalline sample. Dielectric permittivity (ε′) (and dε′/dT) portrays the charge order and other magnetic transitions observed in the magnetization measurement. Dielectric study has revealed a relaxation corresponding to ordering of polarons at ∼60 K that follows Arrhenius behavior both in the presence and absence of magnetic field, and another relaxation was noticed at ∼30 K only under a critical magnetic field (3.2 T) that shows critical slow down of electronic charges obeying power law. Further, the magnetic field induced relaxation shifts to low temperatures with the increase of magnetic field. The observed field induced dielectric relaxation below the reentered charge ordered state is linked with the rapid motions of boundaries of the coexisting phases towards the martensite phase transformation.
Simultaneous immersion Mirau interferometry
Authors: Lyulko Oleksandra V. , Randers-Pehrson Gerhard , Brenner David J.
Published: May 2013

A novel technique for label-free imaging of live biological cells in aqueous medium that is insensitive to ambient vibrations is presented. This technique is a spin-off from previously developed immersion Mirau interferometry. Both approaches utilize a modified Mirau interferometric attachment for a microscope objective that can be used both in air and in immersion mode, when the device is submerged in cell medium and has its internal space filled with liquid. While immersion Mirau interferometry involves first capturing a series of images, the resulting images are potentially distorted by ambient vibrations. Overcoming these serial-acquisition challenges, simultaneous immersion Mirau interferometry incorporates polarizing elements into the optics to allow simultaneous acquisition of two interferograms. The system design and production are described and images produced with the developed techniques are presented.
Note: Nonlinearity error compensated absolute planar position measurement using a two-dimensional phase-encoded binary grating
Authors: Kim Jong-Ahn , Kim Jae Wan , Kang Chu-Shik , Jin Jonghan , Eom Tae Bong
Published: May 2013

This Note presents a new absolute planar position measurement method using a two-dimensional phase-encoded binary grating and a sub-division process where nonlinearity error is compensated inherently. Two orthogonally accumulated intensity profiles of the image of the binary grating are analyzed separately to obtain the absolute position values in each axis. The nonlinearity error caused by the non-ideal sinusoidal signals in the intensity profile is compensated by modifying the configuration of the absolute position binary code and shift-averaging the intensity profile. Using an experimental setup, we measured a circular trajectory of 100 nm radius, and compared the measurement result with that of a laser interferometer. Applying the proposed compensation method, the nonlinearity error was reduced to less than 15 nm.
Atmospheric-pressure air microplasma jets in aqueous media for the inactivation of Pseudomonas fluorescens cells
Authors: Zhang Xianhui , Liu Dongping , Song Ying , Sun Yue , Yang Si-ze
Published: May 2013

The hollow fiber-based cold air microplasma jet array running at atmospheric pressure has been designed to inactivate Pseudomonas fluorescens (P. fluorescens) cells in vitro in aqueous media. The influences of electrode configurations, air flow rate, and applied voltage on the discharge characteristics of the single microplasma jet operating in aqueous media are presented, and the bactericidal efficiency of the hollow fibers-based and large-volume microplasma jet array is reported. Optical emission spectroscopy is utilized to identify excited species during the antibacterial testing of plasma in solutions. These well-aligned and rather stable air microplasma jets containing a variety of short-lived species, such as OH and O radicals and charged particles, are in direct contact with aqueous media and are very effective in killing P. fluorescens cells in aqueous media. This design shows its potential application for atmospheric pressure air plasma inactivation of bacteria cells in aqueous media.
Propagation and enhancement of ultraviolet radiation in metal–dielectric nanocables assisted by surface plasmon polaritons
Authors: Zhuang Qingrui , Yang Zhilin , Kang Junyong
Published: May 2013

Zn/Zn2SiO4 core–shell nanocables are convenient to grow and have ability to carry ultraviolet (UV) information, which makes them a promising structure in the future application, the nano-waveguide amplifier. In this study, the propagation and enhancement characteristics of surface plasmon polaritons in metal–dielectric core–shell nanocables are experimentally and theoretically studied. The strong coupling effect is also determined. The results demonstrate that UV signals can be effectively transmitted and significantly enhanced in the nanocables.
Study of adhesion and chemical bonds in the reaction layer formed at Cu-Mn interconnection/SiO2 interface
Authors: Hino Aya , Okuno Hiroyuki , Kugimiya Toshihiro
Published: May 2013

In this study, adhesion of the Cu/Cu-Mn stacked interconnections to glass (SiO2) substrates was evaluated and the results were correlated with a detailed analysis of the reaction layer between the Cu-Mn and the chemical vapour deposited SiO2. When the Mn concentrations were varied, an abrupt change in the adhesion properties was observed; the practical adhesion properties were obtained in the Cu/Cu-Mn interconnections with Mn concentrations at 8% and higher. To clarify the chemical nature and the microstructure of the reaction layer at the interface between the Cu-x Mn (x = 4, 10 at. %) and the SiO2 layers was analysed using angle-resolved x-ray photoelectron spectroscopy and transmission electron microscope-electron energy loss spectroscopy. These observations indicated that the cross-sectional structure along the reaction layer of the Cu–10 at. % Mn sample can be divided into two regions: in the high Mn region, the Mn-Si complex oxide and the SiO2 mixture phase are preferable due to a decrease in the oxygen fraction near the Cu-Mn layer, whereas in the low Mn region, MnOx and SiO2 mixture are stable. The Mn-Si complex oxide was observed only in the high adhesive sample (Mn 10 at. %). These results suggest that the existence of the chemical bond of the Mn-Si complex oxide improved the interfacial adhesion between the Cu/Cu-Mn stacked interconnections and the glass substrates.
A study of exchange bias in BiFeO3 core/NiFe2O4 shell nanoparticles
Authors: Yusuf S. M. , Manna P. K. , Shirolkar Mandar M. , Kulkarni S. K. , Tewari R. , Dey G. K.
Published: May 2013

We have carried out magnetization measurements on BiFeO3 core/NiFe2O4 shell nanoparticles, and searched for the exchange bias phenomenon in this system. The core-shell nature of these nanoparticles has been established from the transmission electron microscopy images. The neutron diffraction study establishes that the core is G-type antiferromagnetic, while the shell is ferrimagnetic in nature. The search for an exchange bias phenomenon in the core-shell system shows a shift of the field-cooled (FC) hysteresis loops, at 5 K, along the magnetic field axis. The present investigation shows an unusual shift of the zero field-cooled (ZFC) hysteresis loop along the magnetic field axis as well. An enhancement of the remanent magnetization along with a decrease in the coercivity is also observed in the FC case, as compared to the corresponding values in the ZFC case, which is not found commonly in any conventional exchange-biased system. All these features indicate the presence of an interface exchange coupling between core and shell of the studied nanoparticles.
Polarons in crystalline perfluorotetradecanoic acid monohydrate
Authors: Filipič C. , Levstik A. , Hadži D.
Published: May 2013

The ac electrical conductivity and dielectric constant of perfluorotetradecanoic acid monohydrate (PFTDA) were investigated in the frequency range from 1 Hz to 1 MHz and the temperature range from 5 K to 300 K. At temperatures below 300 K, the ac conductivity and dielectric constant follow the universal dielectric response (UDR) typical of hopping or tunneling of localized charge carriers. The analysis of the temperature dependence of the UDR parameter s in terms of the theoretical model for small polarons revealed that below 300 K this mechanism governs the charge transport in PFTDA.
Multilayer silver nanoparticles for light trapping in thin film solar cells
Authors: Shi Yanpeng , Wang Xiaodong , Liu Wen , Yang Tianshu , Xu Rui , Yang Fuhua
Published: May 2013

In this paper, a systematic design and analysis of thin film crystalline silicon solar cells incorporated with a new style of multilayer silver (Ag) nanoparticles (NPs) array is presented. Using numerical simulations, we showed that multilayer Ag NPs provide better light trapping than single layer Ag NPs when the Ag NPs are located on the rear of the solar cell. Furthermore, Ag NP double layers on the rear achieved the best light absorption enhancement for solar cells. Ag NP double layers showed a 6.65% increase in intergraded quantum efficiency across the solar spectrum compared with single layer structures. The parasitic absorption occurring in Ag NP bottom layers was also discussed.
Phase stability of multiferroic GaFeO3 up to 1368 K from in situ neutron diffraction
Authors: Mishra S. K. , Mittal R. , Singh Ripandeep , Zbiri M. , Hansen T. , Schober H.
Published: May 2013

We report a detailed high-temperature powder neutron diffraction investigation of the structural behavior of the multiferroic GaFeO3 between 296 and 1368 K. Temperature dependent neutron diffraction patterns do not show any appreciable change either in intensity or appearance/disappearance of the observed peaks up to 1368 K, ruling out any structural transition in the entire temperature range. Evolution of the distortion of the oxygen polyhedra around Ga1, Ga2, Fe1, and Fe2 cations sites suggest that the Ga1-O tetrahedron is least distorted and Fe1-O is most distorted. Structural features regarding the distortion of polyhedral units would be crucial to understand the temperature dependence of the microscopic origin of polarizations. The electric polarization has been estimated using a simple ionic model and its value is found to decrease with increasing temperature.
Bandgap engineering of rippled MoS2 monolayer under external electric field
Authors: Qi Jingshan , Li Xiao , Qian Xiaofeng , Feng Ji
Published: May 2013

In this letter we propose a universal strategy combining external electric field with the ripple of membrane to tune the bandgap of semiconducting atomic monolayer. By first-principles calculations we show that the bandgap of rippled MoS2 monolayer can be tuned in a large range by vertical external electric field, which is expected to have little effect on MoS2 monolayer. This phenomenon can be explained from charge redistribution under external electric field by a simple model. This may open an avenue of optimizing monolayer MoS2 for electronic and optoelectronic applications by surface patterning.
Effects of operating parameters on ionization distribution in Hall thrusters
Authors: Wei Liqiu , Wang Chunsheng , Zhang Chaohai , Yu Daren
Published: May 2013

In order to study the effects of operating parameters on ionization process, the ionization axial distribution in Hall thrusters are measured through the spectrometry. The relationship between the ionization distribution characteristic parameter (peak value, axial peak position, and width) and operating parameters (discharge voltage, mass flow rate, and magnetic field strength) are given, and the forming conditions of ionization distribution are discussed theoretically.
Band-like transport in high mobility unencapsulated single-layer MoS2 transistors
Authors: Jariwala Deep , Sangwan Vinod K. , Late Dattatray J. , Johns James E. , Dravid Vinayak P. , Marks Tobin J. , Lauhon Lincoln J. , Hersam Mark C.
Published: May 2013

Ultra-thin MoS2 has recently emerged as a promising two-dimensional semiconductor for electronic and optoelectronic applications. Here, we report high mobility (>60 cm2/Vs at room temperature) field-effect transistors that employ unencapsulated single-layer MoS2 on oxidized Si wafers with a low level of extrinsic contamination. While charge transport in the sub-threshold regime is consistent with a variable range hopping model, monotonically decreasing field-effect mobility with increasing temperature suggests band-like transport in the linear regime. At temperatures below 100 K, temperature-independent mobility is limited by Coulomb scattering, whereas, at temperatures above 100 K, phonon-limited mobility decreases as a power law with increasing temperature.
Temperature-dependent photoluminescence of Ge/Si and Ge1-ySny/Si, indicating possible indirect-to-direct bandgap transition at lower Sn content
Authors: Ryu Mee-Yi , Harris Tom R. , Yeo Y. K. , Beeler R. T. , Kouvetakis J.
Published: May 2013

Temperature (T)-dependent photoluminescence (PL) has been investigated for both p-Ge and n-Ge1-ySny films grown on Si substrates. For the p-Ge, strong direct bandgap (ED) along with weak indirect bandgap related (EID) PL at low temperatures (LTs) and strong ED PL at room temperature (RT) were observed. In contrast, for the n-Ge1-ySny, very strong dominant EID PL at LT and strong ED PL were observed at RT. This T-dependent PL study indicates that the indirect-to-direct bandgap transitions of Ge1-ySny might take place at much lower Sn contents than the theory predicts, suggesting that these Ge1-ySny could become very promising direct bandgap semiconductors.
Measuring the fracture resistance of hard coatings
Authors: Liu S. , Wheeler J. M. , Howie P. R. , Zeng X. T. , Michler J. , Clegg W. J.
Published: May 2013

A way of characterizing cracking in a hard coating is described. Microscale double cantilever beams have been made by focused ion beam milling and compressed in situ using a nanoindenter. The method can account for frictional effects and is demonstrated first on single crystals of SiC and GaAs of known toughness, before studying cracking in CrN-based hard coatings. It is found that ultra-fine grained CrAlN/Si3N4 coatings have a toughness approximately twice that of a conventional CrN coating. Although grain-size effects are still unclear, in situ observations directly show crack interactions with particles of Cr and voids in the film.
Attosecond pulse generation in carbon K-edge region (284 eV) with sub-250 μJ driving laser using generalized double optical gating method
Authors: Mashiko Hiroki , Oguri Katsuya , Sogawa Tetsuomi
Published: May 2013

We studied attosecond pulse generation in the carbon K-edge region with generalized double optical gating, which provides a temporal gate for a near-infrared driving laser in high harmonic generation. Since the technique selectively generates the harmonics from the peak of driving laser field, the cutoff component is emphasized in the spectrum. Consequently, the harmonics was achieved up to 284 eV using a driving laser with sub-250 μJ pulse energy. The spectrum supported 20-as duration. The driving laser pulse energy is the lowest value ever reported for high harmonic generation in the carbon K-edge region.
Large out-of-plane ferroelectric polarization in flat epitaxial BaTiO3 on CoFe2O4 heterostructures
Authors: Dix N. , Fina I. , Bachelet R. , Fàbrega L. , Kanamadi C. , Fontcuberta J. , Sánchez F.
Published: May 2013

Engineering interfaces in perovskite/spinel heterostructures is challenged by structural differences. We have used kinetic growth limitations to fabricate flat BaTiO3/CoFe2O4 (BTO/CFO) epitaxial bilayers on La2/3Sr1/3MnO3/SrTiO3(001). In situ analysis of lattice strain during growth has revealed that BTO grows relaxed on highly lattice-mismatched CFO, thus suppressing tensile epitaxial stress effects. As a result, BTO is ferroelectric along the out-of-plane direction with bulk-like polarization. These results show that very high lattice mismatch in heteroepitaxy can be an opportunity rather than a limitation to integrate dissimilar materials with optimized functional properties.
Thermal conductivity of core-shell nanocomposites for enhancing thermoelectric performance
Authors: Poon S. J. , Petersen A. S. , Wu Di
Published: May 2013

The differential effective medium method (DEM) is presented from a physical viewpoint and employed to calculate the lattice thermal conductivity of nano-bulk composites comprising core-shell particles. Extended from the average-T-matrix single-particle approximation, DEM incorporates multiparticle effect essential for the study of core-shell nanocomposites (CSN). Interparticle boundary scattering in addition to intraparticle boundary scattering in CSN is found to add to the reduction of thermal conductivity of nanocomposites. Thus, CSN hold the promise of improving the thermoelectric dimensionless figure of merit ZT above that of monolithic nano-bulk phases. Si and SiGe based CSN serve as illustrative examples.
Giant exchange bias in a single-phase magnet with two magnetic sublattices
Authors: Sun Y. , Cong J.-Z. , Chai Y.-S. , Yan L.-Q. , Zhao Y.-L. , Wang S.-G. , Ning W. , Zhang Y.-H.
Published: May 2013

Exchange bias phenomenon is generally ascribed to the exchange coupling at the interfaces between ferromagnetic and antiferromagnetic layers. Here, we propose a bulk form of exchange bias in a single-phase magnet where the coupling between two magnetic sublattices induces a significant shift of the coercive field after a field cooling. Our experiments in a complicated magnet YbFe2O4 demonstrate a giant exchange bias at low temperature when the coupling between the Yb3+ and Fe2+/Fe3+ sublattices take places. The cooling magnetic field dependence and the training effect of exchange bias are consistent with our model. In strong contrast to conventional interfacial exchange bias, this bulk form of exchange bias can be huge, reaching the order of a few Tesla.
Atomic-scale chemical quantification of oxide interfaces using energy-dispersive X-ray spectroscopy
Authors: Lu Ping , Xiong Jie , Van Benthem Mark , Jia Quanxi
Published: May 2013

Atomic-scale quantification of chemical composition across oxide interfaces is important for understanding physical properties of epitaxial oxide nanostructures. Energy-dispersive X-ray spectroscopy (EDS) in an aberration-corrected scanning transmission electron microscope was used to quantify chemical composition across the interface of ferromagnetic La0.7Sr0.3MnO3 and antiferromagnetic BiFeO3 quantum structure. This research demonstrates that chemical composition at atomic columns can be quantified by Gaussian peak-fitting of EDS compositional profiles across the interface. Cation diffusion was observed at both A- and B-sublattice sites; and asymmetric chemical profiles exist across the interface, consistent with the previous studies.
Electrical property measurements of Cr-N codoped TiO2 epitaxial thin films grown by pulsed laser deposition
Authors: Jaćimović J. , Gaál R. , Magrez A. , Forró L. , Regmi M. , Eres Gyula
Published: May 2013

The temperature dependent resistivity and thermo-electric power of Cr-N codoped TiO2 were compared with that of single element N and Cr doped and undoped TiO2 using epitaxial anatase thin films grown by pulsed laser deposition on (100) LaAlO3 substrates. The resistivity plots and especially the thermoelectric power data confirm that codoping is not a simple sum of single element doping. However, the negative sign of the Seebeck coefficient indicates electron dominated transport independent of doping. The narrowing distinction among the effects of different doping methods combined with increasing resistivity of the films with improving crystalline quality of TiO2 suggest that structural defects play a critical role in the doping process.
Effect of warming on the productivity of perennial ryegrass and kikuyu pastures in south-eastern Australia
Authors: Bell Matthew J. , Eckard Richard J. , Harrison Matthew T. , Neal James S. , Cullen Brendan R.
Published: May 2013

Grazed pastures in south-eastern Australia are typically based on temperate (C3) species, such as perennial ryegrass (Lolium perenne). With predictions of warming to occur in this region, there has been growing interest in the performance of more heat-tolerant and deep-rooted subtropical (C4) pasture grasses, such as kikuyu (Pennisetum clandestinum). This study used an existing pasture model to estimate the production of kikuyu compared with the commonly used perennial ryegrass at seven sites in south-eastern Australia, using an historical baseline climate scenario between 1971 and 2010, and the daily temperature of the baseline scenario adjusted by +1, +2, and +3°C to represent potential warming in the future. The seven sites were chosen to represent the range of climatic zones and soil types in the region. First, the model predictions of monthly kikuyu dry matter (DM) production were validated with measured data at Taree, Camden, and Bega, with results showing good agreement. Second, pasture production (t DM/ha), metabolisable energy (ME, MJ/kg DM) content, and ME yield (GJ/ha) were predicted using the baseline and warmer climate scenarios. The study was based on 56 simulations of the factorial arrangement of seven sites × four temperature scenarios × two pastures. The month and annual ME yield of a kikuyu–subterranean clover (Trifolium subterraneum) pasture and a perennial ryegrass–subterranean clover pasture were compared. This study showed that in summer-dominant rainfall locations, where the average maximum temperature is >23°C, kikuyu was a more productive pasture species than perennial ryegrass. In winter-dominant rainfall locations during the warmer months of December–March, kikuyu can provide a useful source of ME when perennial ryegrass is less productive. With warming of up to 3°C at the winter-dominant rainfall sites, the average ME yield per year of kikuyu was predicted to surpass that of perennial ryegrass, but inter-annual variation in kikuyu production was higher. The nutritive value, seasonal distribution of growth, total annual production, and its variability are all important considerations for producers when selecting pasture species.
Uncertainties in estimated phosphorus loads as a function of different sampling frequencies and common calculation methods
Authors: Defew L. H. , May L. , Heal K. V.
Published: May 2013

Water quality monitoring programs are often based upon low-frequency regular sampling regimes from which loads are estimated. In this study, stream flow (Q) and phosphorus concentrations (C) were measured at 2-hourly intervals over a 10-week period between October and December 2006 in a tributary of Loch Leven, Scotland. The dataset was deconstructed to emulate different weekly, daily and composite sampling strategies, the aim being to highlight the large amount of uncertainty and imprecision in estimating total (TP) and soluble reactive (SRP) phosphorus loads on the basis of commonly applied sampling strategies and calculation methods. When based on the full dataset, phosphorus (P) loads estimated from the 2-hourly data were 459 kg TP, 351 kg particulate P (PP) and 78 kg SRP. In contrast, P loads estimated from different weekly, daily and composite sampling regimes and determined by applying seven different calculation methods ranged from 22 to 5028 kg TP, 13 to 4588 kg PP and 7 to 286 kg SRP. The results of this study highlight the large amount of uncertainty and imprecision associated with estimating P loads and contributes to the body of evidence that high-frequency monitoring is necessary if P loads to standing water bodies are to be quantified accurately and the effects of nutrient management programs interpreted correctly.
Establishment of reference or baseline conditions of chemical indicators in New Zealand streams and rivers relative to present conditions
Authors: McDowell R. W. , Snelder T. H. , Cox N. , Booker D. J. , Wilcock R. J.
Published: May 2013

The management of streams and rivers can be aided by knowledge of reference conditions. Data from >1000 sites across New Zealand was used to develop a technique to estimate median ammoniacal-N, clarity, Escherichia coli, filterable reactive phosphorus, nitrate-N, suspended solids, and total nitrogen and phosphorus values under reference conditions for streams and rivers as classified by the River Environment Classification (REC). The REC enabled us to account for natural variation in climate, topography and geology when estimating reference conditions. Values for minimally disturbed sites (i.e. <5% in intensive agriculture) were generally within the confidence limits for estimated reference values. Metrics that described: (1) the percentage of anthropogenic contribution to analyte values; and (2) the degree of enrichment beyond the reference conditions, showed that lowland sites classified as warm-wet, warm-dry or cool-dry exhibited the greatest anthropogenic input and enrichment. The consideration of natural variation by REC class informs the setting of water quality objectives through avoiding water quality limits or targets that are either too restrictive, and impossible to meet (e.g. below reference conditions), or too high, such that they have little ecological benefit. We recommend reference conditions be considered by regulatory authorities when assessing water quality impacts, objectives and limits.
Trends in water quality of five dairy farming streams in response to adoption of best practice and benefits of long-term monitoring at the catchment scale
Authors: Wilcock Robert J. , Monaghan Ross M. , Quinn John M. , Srinivasan M. S. , Houlbrooke David J. , Duncan Maurice J. , Wright-Stow Aslan E. , Scarsbrook Mike R.
Published: May 2013

Five streams in catchments with pastoral dairy farming as the dominant land use were monitored for periods of 7–16 years to detect changes in response to adoption of best management practices (BMPs). Stream water quality was degraded at the start with respect to N, P, suspended solids (SS) and E. coli concentrations, and was typical of catchments with intensive pastoral agriculture land use. Trend analysis showed a decrease in SS concentration for all streams, generally increasing water clarity, and lower E. coli concentrations in three of the streams. These are attributed to improved stream fencing (cattle exclusion) and greater use of irrigation for treated effluent disposal with less reliance on pond systems discharging to streams. Linkages between water quality and farm actions based on survey data were used to develop BMPs that were discussed at stakeholder workshops. Generic and specific BMPs were developed for the five catchments. The 3–7 year periodicity of major climate cycles, as well as market forces and a slow rate of farmer adoption of simple BMPs mean that monitoring programs in New Zealand need to be much longer than 10 years to detect changes caused by farmer actions. Long-term monitoring is also needed to detect responses to newly legislated requirements for improved water quality.
Convergence of agricultural intensification and climate change in the Midwestern United States: implications for soil and water conservation
Authors: Hatfield J. L. , Cruse R. M. , Tomer M. D.
Published: May 2013

Society faces substantial challenges to expand food production while adapting to climatic changes and ensuring ecosystem services are maintained. A convergence of these issues is occurring in the Midwestern United States, i.e. the ‘cornbelt’ region that provides substantial grain supplies to world markets but is also well known for its contribution to hypoxic conditions in the Gulf of Mexico due to agricultural nutrient losses. This review examines anticipated trends in climate and possible consequences for grain production and soil resource management in this region. The historic climate of this region has been ideal for large-scale agriculture, and its soils are among the world’s most productive. Yet under current trends, degradation of the soil resource threatens our capacity to ensure a stable food supply and a clean environment in the face of a changing climate. A set of strategies and practices can be implemented to meet these challenges by maintaining and improving hydrologic and plant-growth functions of soil, which will improve outcomes for aquatic ecosystems and for the agricultural sector. Soil management ensures our long-term capacity to provide a reliable food supply, and mitigates pressures to expand agricultural practices into marginal croplands that would lead to further environmental degradation.
The precautionary principle, uncertainty and the Noah’s Ark problem
Authors: Perry Neil
Published: May 2013

Multiple biodiversity objectives have been proposed in conservation planning and economics for the Noah’s Ark problem – the problem of allocating limited funds to conservation projects – including species richness, persistence, taxonomic diversity, representativeness, the charismatic value of species, the broader concept of direct utility and ecological importance. However, these objectives are incommensurable and there is little consensus about which objective should be pursued, given the current state of nature. In economics, this is perhaps because the commensurability problem can be solved by converting all biodiversity objectives to monetary values. Yet, even here, a commensurability problem exists because fundamental uncertainty about species interactions means that ecological values cannot be represented in economic terms. Thus, maximising biodiversity value, combined as it is with a rational decision-making framework and assumed known probabilities of survival, can undermine the very values being pursued. This is especially the case when climate change is a current and future state of nature. Climate change adds additional complexity and fundamental uncertainties to the survival probabilities, the future value of species, the interactions among species and the probability of success of conservation projects. The associated incomplete information can lead decision makers to risky decisions under the current approach. Instead, under such conditions, the precautionary principle is appropriate. This leads to a broad conservation strategy of minimising the maximum regret and, when applied to the Noah’s Ark problem, an objective of ecosystem resilience or functional diversity rather than an objective based on economic values. The paper therefore provides an economic justification for focussing conservation resources and threatened species legislation on the resilience of ecosystems.
Bats and bat-borne diseases: a perspective on Australian megabats
Authors: Ng Justin H. J. , Baker Michelle L.
Published: May 2013

Bats are the second most species rich and abundant group of mammals and display an array of unique characteristics but are also among the most poorly studied mammals. They fill an important ecological niche and have diversified into a wide range of habitats. In recent years, bats have been implicated as reservoirs for some of the most highly pathogenic emerging and re-emerging infectious diseases reported to date, including SARS-like coronavirus, Ebola, Hendra and Nipah viruses. The ability of bats to harbour these viruses in the absence of clinical signs of disease has resulted in a resurgence of interest in bat biology and virus–host interactions. Interest in bats, in Australia in particular, has intensified following the identification of several novel bat-borne viruses from flying-foxes, including Hendra virus, which is capable of spillover from bats to horses and subsequently to humans with potentially fatal consequences. As we continue to encroach on the natural habitats of bats, a better understanding of bat biology, ecology and virus–host interactions has never before been so critical. In this review, we focus on the biology of Australian pteropid bats and the pathogens they harbour, summarising current knowledge of bat-borne diseases, bat ecology, ethology and immunology.
Dnmt2-dependent methylomes lack defined DNA methylation patterns
Authors: Raddatz Günter , Guzzardo Paloma M. , Olova Nelly , Fantappié Marcelo Rosado , Rampp Markus , Schaefer Matthias , Reik Wolf , Hannon Gregory J. , Lyko Frank
Published: May 2013

Several organisms have retained
methyltransferase
2 (
Dnmt2
) as their only candidate DNA methyltransferase gene. However, information about Dnmt2-dependent methylation patterns has been limited to a few isolated loci and the results have been discussed controversially. In addition, recent studies have shown that
Dnmt2
functions as a tRNA methyltransferase, which raised the possibility that
Dnmt2
-only genomes might be unmethylated. We have now used whole-genome bisulfite sequencing to analyze the methylomes of
Dnmt2
-only organisms at single-base resolution. Our results show that the genomes of
Schistosoma mansoni
and
Drosophila melanogaster
lack detectable DNA methylation patterns. Residual unconverted cytosine residues shared many attributes with bisulfite deamination artifacts and were observed at comparable levels in
Dnmt2
-deficient flies. Furthermore, genetically modified
Dnmt2
-only mouse embryonic stem cells lost the DNA methylation patterns found in wild-type cells. Our results thus uncover fundamental differences among animal methylomes and suggest that DNA methylation is dispensable for a considerable number of eukaryotic organisms.
Interferon-gamma release assays in the diagnosis of latent tuberculosis infection.
Authors: Ajit Lalvani Ajit Lalvani , Manish Pareek Manish Pareek
Published: May 2013

This chapter describes the worldwide burden and methods of diagnosing latent tuberculosis infection. The clinical performance of interferon-gamma release assays (IGRAs) in different populations, including immunocompetent and immunocompromised (HIV, immune-mediated inflammatory diseases) persons, and the predictive value of IGRAs for progression to active tuberculosis are reviewed. The incorporation of IGRAs into international public health guidelines and its use in treatment monitoring and future directions are discussed.
Role of phenotypic methods for drug susceptibility testing of M. tuberculosis isolates in the era of MDR and XDR epidemics.
Authors: Heifets L.
Published: May 2013

This chapter discusses the role of phenotypic methods for drug susceptibility testing of Mycobacterium tuberculosis isolates in timely detection and management of patients with multiple drug resistant (MDR) and extremely drug resistant (XDR) tuberculosis. The different methods and their combinations, as well as their affordability/cost, are described.