bluuebunny/crossref_metadata_2025 huggingface dataset:
Chromosome evolution with naked eye: Palindromic context of the life origin
Authors: Larionov Sergei , Loskutov Alexander , Ryadchenko Eugeny
Published: February 2008

Based on the representation of the DNA sequence as a two-dimensional (2D) plane walk, we consider the problem of identification and comparison of functional and structural organizations of chromosomes of different organisms. According to the characteristic design of 2D walks we identify telomere sites, palindromes of various sizes and complexity, areas of ribosomal RNA, transposons, as well as diverse satellite sequences. As an interesting result of the application of the 2D walk method, a new duplicated gigantic palindrome in the X human chromosome is detected. A schematic mechanism leading to the formation of such a duplicated palindrome is proposed. Analysis of a large number of the different genomes shows that some chromosomes (or their fragments) of various species appear as imperfect gigantic palindromes, which are disintegrated by many inversions and the mutation drift on different scales. A spread occurrence of these types of sequences in the numerous chromosomes allows us to develop a new insight of some accepted points of the genome evolution in the prebiotic phase.
Comparative electron magnetic resonance study of magnetic ordering in La1−xCaxMnO3 (x=0.1,0.3) bulk and nanometer sized manganite crystals
Authors: Shames A. I. , Auslender M. , Rozenberg E. , Sominski E. , Gedanken A. , Mukovskii Ya. M.
Published: February 2008

To check the impact of nanosize originated effects on the magnetic ordering in doped manganites, X-band electron magnetic resonance measurements were performed in 5K⩽T⩽600K interval on nanometer sized and bulk crystals of La1−xCaxMnO3 (x=0.1,0.3). The analysis of electron paramagnetic resonance parameters together with the data of magnetic measurements shows that bulk La0.9Ca0.1MnO3 is characterized by inhomogeneous confinement of charge carriers, leading to its mixed magnetic ordering. The nanocrystals of the same composition show the carrier mobility within impuritylike band, which induces ferromagneticlike ground state. The bulk La0.7Ca0.3MnO3 demonstrates homogeneous ferromagnetism and bandlike carriers mobility. The surface magnetic disorder in its nanocounterpart leads to appearance of two magnetic phases—core phase (bulklike in properties) and a surface one with notably reduced temperature of magnetic ordering. It appears that neither double exchange interaction nor carrier mobility exists between these phases.
Phenomenological vector models of hysteresis driven by random fluctuation fields
Authors: Andrei Petru , Adedoyin Ayodeji
Published: February 2008

The vectorial properties of thermal relaxation phenomena are modeled by using random fluctuation fields that act as perturbations on the external applied magnetic field. The total magnetic field is used as input in phenomenological vector models of hysteresis, which, in this article, are defined as superposition of scalar models of hysteresis distributed along all possible directions. A Monte Carlo technique is developed to compute the average value of the magnetization vector as a function of time. Whereas in the case of isotropic materials the average value of the magnetization vector usually moves on a straight line oriented towards the direction of the applied field, in the case of anisotropic materials the magnetization vector can switch from one easy axis to another and cross the direction of the applied field. It is shown that, depending on the initial hysteretic state, the trajectory of the magnetization vector can deviate substantially from the straight line, which is a pure three-dimensional relaxation effect.
Optical bistability in one-dimensional magnetic photonic crystal with two defect layers
Authors: Lyubchanskii I. L. , Dadoenkova N. N. , Zabolotin A. E. , Lee Y. P. , Rasing Th.
Published: February 2008

One-dimensional magnetic photonic crystal with two magnetic defect layers is theoretically studied. The dependence of defect modes inside photonic band gap on the distance between defect layers is investigated. It is shown that the cubic nonlinear polarization leads to the effect of bistability on the frequencies of defect modes.
Optically spin oriented electron transmission across fully epitaxial Fe3O4∕GaAs(001) interfaces
Authors: Taniyama T. , Mori T. , Watanabe K. , Wada E. , Itoh M. , Yanagihara H.
Published: February 2008

We demonstrate fully epitaxial growth of Fe3O4∕GaAs(001) heterostructures using a reactive molecular beam epitaxy (MBE) method. The Fe3O4 film was obtained by oxidizing an ultrathin Fe layer into an Fe3O4 seed layer in an O2 atmosphere at 260°C, followed by the reactive MBE growth of Fe3O4. The Fe3O4 seed layer effectively works as a template for the successive growth of Fe3O4. Also, a clear spin filtering effect of optically spin oriented electrons at the Fe3O4∕GaAs(001) interface is shown at room temperature. The results clearly demonstrate that the spin filtering effect occurs at the Fe3O4∕GaAs(001) interface and has its origin in the spin split density of states of the Fe3O4 layer.
Effect of nonuniform microstructure on magnetic switching behavior in CoCrPt–SiO2 perpendicular magnetic recording media
Authors: Jung H. S. , Kuo M. , Malhotra S. S. , Bertero G.
Published: February 2008

The effect of nonuniform microstructure on magnetic switching behavior for CoCrPt–SiO2 single layer media with oxygen contents (OCs) from 4% to 10% and recording layer thickness (tmag) from 2to27nm is investigated. Plan-view transmission electron microscopy images clearly show nonuniform microstructure of CoCrPt–SiO2 with OC=10% along the film thickness direction: poor grain isolation at a thin layer, excellent grain isolation at a medium layer, and formation of subgrains at a thick layer. The highest coercivity (Hc) is not observed on the medium with the best grain isolation. An initial CoPt layer with less grain isolation forms on top of Ru interlayer with increasing OC in films. It exhibits domain wall switching, resulting in significant incoherent switching. This is consistent with large magnetic activation volume at tmag⩽6nm. Other plausible incoherent switching mechanism for thicker layer media showing low Hc is likely due to formation of subgrains with less grain isolation.
Origin and control of ferromagnetism in dilute magnetic semiconductors and oxides (invited)
Authors: Dietl Tomasz
Published: February 2008

The author reviews the present understanding of the hole-mediated ferromagnetism in magnetically doped semiconductors and oxides as well as the origin of high temperature ferromagnetism in materials containing no valence band holes. It is argued that in these systems spinodal decomposition into regions with a large and a small concentration of magnetic component takes place. This self-organized assembling of magnetic nanocrystals can be controlled by codoping and growth conditions. Functionalities of these multicomponent systems are described together with prospects for their applications in spintronics, nanoelectronics, photonics, plasmonics, and thermoelectrics.
Large magnetoresistance in Si:B-SiO2-Al structures
Authors: Schoonus J. J. H. M. , Kohlhepp J. T. , Swagten H. J. M. , Koopmans B.
Published: February 2008

A magnetic-field-dependent resistance change of eight orders of magnitude is observed in boron-doped Si-SiO2-Al structures. In order to identify the elementary mechanisms governing this phenomenon, the thickness of the oxidic layer, which is used as an interface energy barrier, has been varied by changing the exposure time to an oxygen plasma. Next, the chemical composition has been monitored by in situ x-ray photoelectron spectroscopy measurements. From current-voltage measurements, we observe that at low temperatures, an ultrathin SiO2 layer provides the kinetic energy to trigger an autocatalytic process of impact ionization. A magnetic field suppresses the onset of impact ionization to higher electric fields, resulting in a large magnetoresistance.
The pinning role of nonferromagnetic β phase in the domain wall motion of ferromagnetic MnAs film on GaAs(001)
Authors: Ryu Kwang-Su , Lee Hun-Sung , Shin Sung-Chul , Akinaga Hiro
Published: February 2008

We report the pinning role of the nonferromagnetic β phase in the domain wall motion of ferromagnetic MnAs film on GaAs(001) in the temperature range of 20–35°C. The dependence of the coercivity on the applied field direction at all temperatures was found to follow an inverse cosine law, as expected from a theoretical model considering the domain wall motion in ferromagnetic films. From this analysis, it was found that the domain wall pinning energy density increases as the temperature increases. This is ascribed to the increase in the volume fraction of the nonferromagnetic β phase, resulting in an increase of the domain wall pinning effect during the domain wall motion.
Quantifying the synchronizability of externally driven oscillators
Authors: Stefański Andrzej
Published: February 2008

This paper is focused on the problem of complete synchronization in arrays of externally driven identical or slightly different oscillators. These oscillators are coupled by common driving which makes an occurrence of generalized synchronization between a driving signal and response oscillators possible. Therefore, the phenomenon of generalized synchronization is also analyzed here. The research is concentrated on the cases of an irregular (chaotic or stochastic) driving signal acting on continuous-time (Duffing systems) and discrete-time (Henon maps) response oscillators. As a tool for quantifying the robustness of the synchronized state, response (conditional) Lyapunov exponents are applied. The most significant result presented in this paper is a novel method of estimation of the largest response Lyapunov exponent. This approach is based on the complete synchronization of two twin response subsystems via additional master-slave coupling between them. Examples of the method application and its comparison with the classical algorithm for calculation of Lyapunov exponents are widely demonstrated. Finally, the idea of effective response Lyapunov exponents, which allows us to quantify the synchronizability in case of slightly different response oscillators, is introduced.
Micromagnetic study of full widths at half maximum in spin-transfer-driven self-oscillations of individual nanomagnets
Authors: Carpentieri M. , Torres L. , Finocchio G. , Azzerboni B.
Published: February 2008

A full micromagnetic study of the spin-transfer-driven self-oscillations of individual ellipsoidal PyCu nanomagnets as small as 30×90×5.5nm3 is presented. The magnetic parameters have been computed by fitting static magnetoresistance measurements. The main mode found in the experiments by Sankey et al. [Phys. Rev. Lett. 96, 227601 (2006)] is analyzed. The full width at half maximum is calculated without taking into account the effect of thermal activation. The full width is found to decrease from 6.5to3.3MHz when increasing the current in the self-oscillation region. These narrow widths are mainly produced by the nonuniformities of the magnetization and since they are computed at zero temperature mark a limit for the spectral purity of the self-oscillations in those nanomagnets.
Superheating and melting of nanocavities
Authors: Ouyang G. , Li X. L. , Yang G. W.
Published: February 2008

Melting behaviors of nanocavities in matrix is investigated on the basis of thermodynamics in terms of continuum mechanics at the nanometer scale. An analytical model is developed to elucidate the void shrinking kinetics and the void melting behavior. It is found that the shrinkage of nanocavities exhibits a pronounced nonlinear kinetic character when the nanocavity’s size goes into several nanometer scales. The giant superheating of the nanocavity with the small size appears when the temperature is higher than the melting point of the matrix. The size dependence of the inner surface energy of nanocavities seems responsible for these anomalous melting behaviors.
Monitoring cutting tool operation and condition with a magnetoelastic rate of change of torque sensor
Authors: Garshelis Ivan J. , Kari Ryan J. , Tollens Stijn P. L. , Cuseo James M.
Published: February 2008

Application of a magnetoelastic rate of change of torque sensor to monitor the condition of milling cutters and operating parameters is described. Cutting tools naturally degrade with use by wear, chipping, or fracture, and the efficiency and quality of the product are highly dependent on the tool condition. The theoretical analysis is compared to experimental data in detecting changes in torque during each cutting event, and the rate of change of torque signal is investigated for a variety of cutting tool conditions.
Comparison of different methods for calculating the paramagnetic relaxation enhancement of nuclear spins as a function of the magnetic field
Authors: Belorizky Elie , Fries Pascal H. , Helm Lothar , Kowalewski Jozef , Kruk Danuta , Sharp Robert R. , Westlund Per-Olof
Published: February 2008

The enhancement of the spin-lattice relaxation rate for nuclear spins in a ligand bound to a paramagnetic metal ion [known as the paramagnetic relaxation enhancement (PRE)] arises primarily through the dipole-dipole (DD) interaction between the nuclear spins and the electron spins. In solution, the DD interaction is modulated mostly by reorientation of the nuclear spin-electron spin axis and by electron spin relaxation. Calculations of the PRE are in general complicated, mainly because the electron spin interacts so strongly with the other degrees of freedom that its relaxation cannot be described by second-order perturbation theory or the Redfield theory. Three approaches to resolve this problem exist in the literature: The so-called slow-motion theory, originating from Swedish groups [Benetis et al., Mol. Phys. 48, 329 (1983); Kowalewski et al., Adv. Inorg. Chem. 57, (2005); Larsson et al., J. Chem. Phys. 101, 1116 (1994); T. Nilsson et al., J. Magn. Reson. 154, 269 (2002)] and two different methods based on simulations of the dynamics of electron spin in time domain, developed in Grenoble [Fries and Belorizky, J. Chem. Phys. 126, 204503 (2007); Rast et al., ibid. 115, 7554 (2001)] and Ann Arbor [Abernathy and Sharp, J. Chem. Phys. 106, 9032 (1997); Schaefle and Sharp, ibid. 121, 5387 (2004); Schaefle and Sharp, J. Magn. Reson. 176, 160 (2005)], respectively. In this paper, we report a numerical comparison of the three methods for a large variety of parameter sets, meant to correspond to large and small complexes of gadolinium(III) and of nickel(II). It is found that the agreement between the Swedish and the Grenoble approaches is very good for practically all parameter sets, while the predictions of the Ann Arbor model are similar in a number of the calculations but deviate significantly in others, reflecting in part differences in the treatment of electron spin relaxation. The origins of the discrepancies are discussed briefly.
On the Euclidean version of the photon number integral
Authors: Ruijsenaars S. , Stodolsky L.
Published: February 2008

We reconsider the Euclidean version of the photon number integral introduced by Stodolsky [Acta Phys. Pol. B 33, 2659 (2002), e-print hep-th/02053131].This integral is well defined for any smooth non-self-intersecting curve in RN. Besides studying general features of this integral (including its conformal invariance), we evaluate it explicitly for the ellipse. The result is nellipse=(ξ−1+ξ)π2, where ξ is the ratio of the minor and major axes. This is in agreement with the previous result ncircle=2π2 and also with the conjecture that the minimum value of n for any plane curve occurs for the circle.
Suppression of stimulated Raman scattering of a laser in a rippled density plasma
Authors: Pathak Vishwa Bandhu , Tripathi V. K.
Published: February 2008

The effect of a stationary electron density ripple on stimulated Raman scattering (SRS) of a laser in a plasma is studied. The density ripple couples with the primary Langmuir wave, generated in the Raman process, to produce a secondary Langmuir wave of larger wave number that is strongly Landau damped on the electrons. As a consequence, the growth rate of the Raman process is suppressed. In a special case of density ripple produced by two counterpropagating lasers of intensity ∼1015W∕cm2 at 1μm wavelength in a 6% critical density plasma of 1keV temperature, the reduction in growth rate is substantial. The effect of density ripple wavelength on SRS is studied at different plasma temperatures. Up to ∼70% suppression in SRS is observed for different plasma temperatures at different ripple wavelengths. However, for higher temperatures we also get ∼10% of suppression for the other ripple wavelength values.
Cross-sectional transmission electron microscopy observations of structural damage in Al0.16Ga0.84N thin film under contact loading
Authors: Jian Sheng-Rui , Juang Jenh-Yih , Lai Yi-Shao
Published: February 2008

This article reports a nanomechanical response study of the contact-induced deformation behavior in Al0.16Ga0.84N thin film by means of a combination of nanoindentation and the cross-sectional transmission electron microscopy (XTEM) techniques. Al0.16Ga0.84N thin film is deposited by using the metal-organic chemical vapor deposition method. Hardness and Young’s modulus of the Al0.16Ga0.84N films were measured by a Berkovich nanoindenter operated with the continuous contact stiffness measurements mode. The obtained values of the hardness and Young’s modulus are 19.76±0.15 and 310.63±9.41 GPa, respectively. The XTEM images taken in the vicinity just underneath the indenter tip revealed that the multiple “pop-ins” observed in the load-displacement curve during loading are due primarily to the activities of dislocation nucleation and propagation. The absence of discontinuities in the unloading segments of the load-displacement curve suggests that no pressure-induced phase transition was involved.
Enhanced hole injection and transport in molybdenum-dioxide-doped organic hole-transporting layers
Authors: Matsushima Toshinori , Adachi Chihaya
Published: February 2008

We have found that molybdenum dioxide (MoO2) is an excellent dopant for enhancing electrical conductivities in organic hole-transporting layers. We fabricated hole-only devices with an alpha-sexithiophene (α-6T) layer doped with MoO2 at various concentrations to investigate how doping MoO2 into the α-6T layers influences the hole-injection and hole-transport characteristics of these layers. We observed a marked increase in electrical conductivity as a result of the MoO2 doping. The 30-mol % MoO2-doped α-6T layer had a high electrical conductivity of 8.9±1.3×10−6 S/cm. From the results of our visible/near-infrared absorption spectra study of these doped layers, we confirmed that this increase in electrical conductivity is caused by a charge transfer between MoO2 and α-6T, which leads to an increase in free hole concentration in the doped layers and the formation of an ohmic contact at an electrode/α-6T interface. In the latter part of this paper, we discuss current flow and electroluminescence (EL) characteristics of organic light-emitting diodes (OLEDs) with a 30-mol % MoO2-doped α-6T hole-transporting layer and a 30-mol % Cs-doped phenyldipyrenylphosphine oxide (POPy2) electron-transporting layer. We achieved an extremely low driving voltage of 3.1 V required for a current density of 100 mA/cm2 in the doped OLEDs owing to the use of the α-6T and POPy2 layers with high carrier mobilities and the excellent p-type MoO2 and n-type Cs dopants. We demonstrated the enhancement of power efficiencies by ≈2 times in the doped OLEDs compared with undoped OLEDs and observed bright EL at low driving voltages in the doped OLEDs, for example, 100 cd/m2 at 2.3 V, 1000 cd/m2 at 2.7 V, and 10 000 cd/m2 at 3.3 V.
Formation of a low energy grain boundary in ZnO: The structural unit concept in hexagonal symmetry materials
Authors: Ruterana P. , Abouzaid M. , Béré A. , Chen J.
Published: February 2008

ZnO thin films prepared by magnetron sputtering on c-plane sapphire may exhibit a columnar growth with an average column diameter depending on the deposition temperature. In this case two epitaxial relationships coexist and adjacent columns are rotated, one from the other, by 90° around the [0001] direction. The long range rotation between domains is in agreement with the theoretical epitaxial relationships, but the local angles oscillate between 27° and 32° due to the formation of interfaces, which settle into low energy configurations with grain boundary dislocations of a Burgers vectors and 5/7 aligned structural units for the 32.2° tilt angle.
Carrier lifetime measurement in n− 4H-SiC epilayers
Authors: Klein P. B.
Published: February 2008

The effects of measurement technique and measurement conditions (e.g., injection level, temperature) on measured carrier lifetimes in n− 4H-SiC epilayers are investigated both experimentally and through detailed carrier dynamics simulations to better understand differences between reported lifetimes. Three common, optically based techniques are compared: time resolved photoluminescence, transient free carrier absorption, and microwave photoconductivity decay. From the details of these measurement techniques it is shown from both theory and experiment that for the limits of high or low injection, these techniques can reflect very different lifetimes. The effect of measurement conditions on the carrier lifetime was approached by simulating the carrier dynamics assuming a dominant Z1/Z2 defect in order to calculate the evolution of the lifetimes and the carrier and defect charge state concentrations for arbitrary injection level or temperature, as a closed-form solution to this problem does not exist. The simulated behavior was found to be in reasonable agreement with experiment and the resulting values for the electron and hole capture cross sections for the 0/+ transition of Z1/Z2 were found to be σn2≈(2−4)×10−15 cm2 and σp2≈(1−2)×10−14 cm2, respectively. The simulations provide insight into the dominant processes controlling the lifetime and identify four distinct stages of decay. A simple expression for the ratio of high- to low-injection lifetimes is presented which compares well with experiment. The temperature dependence of the lifetime is found to be relatively weak below 500 K and thermally activated immediately above this temperature due to electron emission from the Z0 state. Electron emission from Z− and hole emission become important only at higher temperatures. Simulations with both Z1/Z2 and EH6/EH7 defects suggest the latter does not contribute significantly to the lifetime in as-grown epilayers, due primarily to a small capture cross section for holes.
Magnetic characterization of magnetic tunnel junction devices using circle transfer curves
Authors: Safron N. S. , Schrag B. D. , Liu Xiaoyong , Shen Weifeng , Mazumdar D. , Carter M. J. , Xiao Gang
Published: February 2008

We describe new characterization methods that allow an accurate determination of all of the magnetic parameters that govern the behavior of magnetoresistive devices. These characterization methods are explained and used to measure the magnetic properties of MgO-based magnetic tunnel junction (MTJ) devices with magnetoresistance values of over 150%. We will show that the analysis of so-called “circle transfer curves,” which are measurements of the device magnetoresistance in a rotating, constant-magnitude applied field, can accurately determine the magnitude and direction of the free layer anisotropy as well as the pinned layer orientation and exchange bias strength. We also show how a measurement of the MTJ’s remnant resistance curve, obtained by saturating the MTJ at different field angles and then removing the applied field, can provide additional information on the free layer anisotropy characteristics. We will also compare our results with values extracted from traditional Stoner-Wohlfarth asteroid curves. Finally, we show that the extracted parameters can accurately predict the shape of traditional MTJ transfer curves.
Neutron diffraction studies of magnetostrictive Fe–Ga alloy ribbons
Authors: Zhao Xuegen , Mellors Nigel , Kilcoyne Susan , Lord Don , Lupu Nicoleta , Chiriac Horia , Henry Paul F.
Published: February 2008

Melt-spun Fe–Ga ribbons were prepared and some ribbons were annealed at 1000°C for 1h then slowly cooled to room temperature. X-ray diffraction patterns revealed no evidence of texture and only bcc phase in the as-quenched ribbons. However, high-resolution neutron diffraction patterns gave more information on the structure of these ribbons. Only diffractions from the disordered bcc A2 phase were found in as-quenched ribbons with 15, 17.5, and 19.5at.% Ga content, without any trace of satellite peaks or splitting peaks from the proposed Ga–Ga pairing superlattice structure. The broadening of the base of the (110) peaks for all samples except the as-quenched 15at.% Ga ribbon might indicate the existence of some kind of short range ordering. Ribbons developed L12 phase after annealing especially in the Fe 19.5at.% Ga ribbon where the formation of L12 phase reduced the Ga content in the remaining A2 phase and decreased its lattice parameter dramatically. D03 phase formed in the as-quenched 22.5at.% Ga ribbon and the following annealing treatment transformed more A2 phase into D03 phase.
Electromagnetic beaming from omnidirectional sources by inverse design
Authors: Martínez Alejandro , García Raquel , Håkansson Andreas , Piqueras Miguel A. , Sánchez-Dehesa José
Published: February 2008

Highly directional electromagnetic sources are desirable in a variety of fields and applications. By embedding point sources inside periodic lattices, radiation can be enhanced and confined within a small angular range. However, this directional source is far from perfect. Here, the authors demonstrate that by means of inverse design (ID) the periodic lattice can be modified to further enhance the radiation in a unique spatial direction. Experiments in the microwave regime show that with the ID structure the harvested radiation intensity is almost 60 times higher than for the isolated source and is confined within a 7.5° full width at half maximum angular range.
Ferroelectric and fatigue behavior of Pb(Zr0.52Ti0.48)O3∕(Bi3.15Nd0.85)Ti3O12 bilayered thin films
Authors: Sim C. H. , Zhou Z. H. , Gao X. S. , Soon H. P. , Wang J.
Published: February 2008

Bilayered ferroelectric thin films consisting of Pb(Zr0.52Ti0.48)O3 (PZT) and (Bi3.15Nd0.85)Ti3O12 (BNT) layers have been successfully fabricated via a synthesis route of combining sol-gel and rf sputtering. Both ferroelectric layers are well retained in both PZT/BNT and BNT/PZT bilayered films as suggested by x-ray diffraction and secondary ion mass spectroscopy analyses. Their ferroelectric and dielectric properties are largely dependent on the thicknesses of the constituent layers. An anomalous enhancement in polarization is demonstrated by the PZT/BNT bilayered thin film, whereby the switchable polarization increases dramatically upon >106cycles of polarization switching. The fatigue anomaly observed for the PZT/BNT bilayered thin film is related to the space charges that are accumulated at the interfaces in the heterolayered structure. By comparison, the BNT/PZT bilayered thin film exhibited better ferroelectric behavior than that of the PZT/BNT film where the P-E hysteresis loops were relatively well saturated with higher polarization. The BNT/PZT bilayered thin film also demonstrated a much improvement in fatigue behavior as compared to that of the single layer PZT film.
Direct vapor jet printing of three color segment organic light emitting devices for white light illumination
Authors: Arnold Michael S. , McGraw Gregory J. , Forrest Stephen R. , Lunt Richard R.
Published: February 2008

Organic-vapor jet printing (OVJP) is used to directly pattern small molecular weight electrophosphorescent white organic light-emitting devices (WOLEDs) consisting of parallel stripes of separate red, green, and blue OLEDs. The spatial patterning of the WOLEDs with peak forward viewing external quantum and luminous efficiencies of 7.1±0.3% and 7.0±0.4lm∕W, respectively, is accomplished by transporting the vapors of organic semiconductors through a nozzle to a translating sample substrate. Using multiple color segments to generate white light allows for the individual optimization of each color, is continuously color tunable, and can be used to compensate for differential aging of the constituent dopants. The theory and experimental results of WOLED printing via OVJP are discussed.
30
kV
and 3kA semi-insulating GaAs photoconductive semiconductor switch
Authors: Shi Wei , Tian Liqiang , Liu Zheng , Zhang Linqing , Zhang Zhenzhen , Zhou Liangji , Liu Hongwei , Xie Weiping
Published: February 2008

Current as high as 3.7kA has been generated using a single photoconductive semiconductor switch (PCSS) excited by a laser pulse with the energy of ∼8mJ and under a bias of 28kV. The PCSS with electrode gap of 14mm was fabricated from semi-insulating GaAs. Under different bias voltages the “on” resistances of the PCSS were measured. The longevity of the PCSS reached 350 shots at 20kV and 400A. The breakdown mechanism of the PCSS is analyzed based on the breakdown characteristics. It is shown that the breakdown of GaAs PCSS can be described by the electron-trapping breakdown theory.
Magnetoelectric effects in composite of nanogranular Fe∕TiO2−δ films
Authors: Yoon S. D. , Vittoria C. , Srivastava Y. N. , Widom A. , Harris V. G.
Published: February 2008

Employing a new experimental technique to measure magnetoelectric response functions, we have measured the magnetoelectric effect in composite films of nanogranular metallic iron in anatase titanium dioxide at temperatures below 50K. A magnetoelectric resistance is defined as the ratio of a transverse voltage to bias current as a function of magnetic field. In contrast to the anomalous Hall resistance measured above 50K, the magnetoelectric resistance below 50K is significantly larger and exhibits an even symmetry with respect to magnetic field reversal H→−H. The composite films are unique in terms of showing magnetoelectric effects at low temperatures, <50K, and anomalous Hall effects at high temperatures, >50K.
Propagation of a femtosecond pulsed laser ablation plume into a background atmosphere
Authors: Amoruso S. , Bruzzese R. , Wang X. , Xia J.
Published: February 2008

We investigate the effects of ambient gas on the expansion dynamics of laser plume produced during femtosecond laser ablation of a metallic target. We studied experimentally plume propagation for ambient air pressure ranging from 10−6to50mbar, observing that the atomic and nanoparticles plume components experience different effects. We interpret these results with a simplified model of the plume front propagation, which is able to fully reproduce the main experimental features. Our results allow us to estimate quantitatively the nanoparticles plume content (up to about 80%), and can help identifying optimal conditions of nanoparticles deposition for thin films production.
In situ observation of gas reemission and blister rupture during helium implantation in silicon
Authors: Wittmaack Klaus
Published: February 2008

Gas phase ionization mass spectrometry is shown to provide means for exploring the processes that control the retention of 10keV He+ implanted in Si at 45°. Blistering, observed in situ, was preceded by a long period of bombardment (70% of the critical fluence for blistering) during which implanted He was released at a rather high rate (∼33% of the incident He flux). Assisted by the stress due to the growing bubbles, bombardment induced detrapping allows a large fraction of the implanted He atoms to migrate to the nearby surface and escape into vacuum.
Discrimination of quantum dots using an optically created nuclear field
Authors: Sasakura H. , Kaji R. , Adachi S. , Muto S.
Published: February 2008

We investigated an optically created nuclear field in a single InAlAs quantum dot and demonstrated that the nuclear field can be used to discriminate whether photoluminescence lines originate from the same dot or a different dot. Since the nonlinear response of the nuclear field is sensitive to the electron g factor and correlation time of a coupled electron-nuclear spin system, the resultant Overhauser shift is their good measure for individual quantum dots. This method provides a simple and convenient alternative to the standard photon cross-correlation method.
Extractable, elevated ion charge states in the transition regime from vacuum sparks to high current vacuum arcs
Authors: Yushkov Georgy Yu. , Anders André
Published: February 2008

Metal ions were extracted from pulsed discharge plasma operating in the transition region between vacuum spark and vacuum arc. At a peak current of about 4kA, and with a pulse duration of 8μs, we observed mean ion charges states of about 6 for several cathode materials. In the case of platinum, the highest average charge state was 6.74 with charge states present as high as 10, and with gold we found traces of charge state 11. At higher currents, nonmetallic contaminants started to dominate the ion beam, preventing further enhancement of the metal charge states.
Effective-medium models and experiments for extraordinary transmission in metamaterial-loaded waveguides
Authors: Xu Hao , Wang Zhiyu , Hao Jiaming , Dai Jiajie , Ran Lixin , Kong J. A. , Zhou L.
Published: February 2008

We show that a metallic waveguide behaves as an electric (magnetic) plasma for transverse-electric (transverse-magnetic) polarized electromagnetic (EM) waves at frequencies below cutoff value. Inserting anisotropic resonance structures of either electric or magnetic type into a waveguide, we find extraordinary transmissions of EM waves with different polarizations through the waveguide at frequencies well below the waveguide’s cutoff value, following two different mechanisms. Microwave experiments, in excellent agreements with finite-different-time-domain simulations, are performed to demonstrate all theoretical predictions.
Experimental evidence of ballistic transport in cylindrical gate-all-around twin silicon nanowire metal-oxide-semiconductor field-effect transistors
Authors: Cho K. H. , Yeo K. H. , Yeoh Y. Y. , Suk S. D. , Li M. , Lee J. M. , Kim M.-S. , Kim D.-W. , Park D. , Hong B. H. , Jung Y. C. , Hwang S. W.
Published: February 2008

We have investigated the electrical characteristics of cylindrical gate-all-around twin silicon nanowire metal-oxide-semiconductor field effect-transistors with 4nm radius and the gate length ranging from 22to408nm. We observed strong transconductance overshoot in the linear source-drain bias regime in the devices with channel length shorter than 46nm. The mean free path estimated from the slope of the zero-field one dimensional ballistic resistance measured as a function of device length was almost the same as this length.
Self-written active waveguide for integrated optical amplifiers
Authors: Yamashita K. , Fukuzawa E. , Kitanobou A. , Oe K.
Published: February 2008

The authors propose a fabrication method of optical amplifying devices, which is based on a technique of light-induced self-written waveguide. The waveguide structure doped with infrared organic dye molecules was self-written by visible laser light irradiation from optical fiber tips to photopolymerized resin, which makes the waveguide self-aligned with input and output fibers. The self-written “active” waveguides with the length of 0.98–1.89mm were fabricated and amplified spontaneous emission at ∼790nm was observed. Furthermore, optical amplification of externally input light was also implied in a tentative examination.
Theoretical evidence of a superconducting transition in doped silicon and germanium driven by a variation of chemical composition
Authors: Kádas K. , Vitos L. , Ahuja R.
Published: February 2008

We present the first theoretical evidence of chemical composition driven superconductivity in acceptor-doped silicon and germanium, using density functional theory. We examine the concentration dependence of Tc in B-doped Si and Ge and predict that B-doped Ge is a superconductor with a slightly higher Tc than B-doped Si. We show that there is a critical concentration above which B-doped Si and Ge become superconducting and estimate it to be ∼2.6% in Si:B and ∼2.2% in Ge:B. Considering the Al-doped Si and Ge, we point out the decisive role of the chemical element in the hole-doping scenario.
Tunable energy transfer efficiency based on the composite of mixed CdSe quantum dots and elastomeric film
Authors: Chen C. W. , Wang C. H. , Chen Y. F. , Lai C. W. , Chou P. T.
Published: February 2008

We demonstrate a facile and general approach to investigate the dependence of energy transfer on the separation distance between proximal mixed-size quantum dots. Without varying the mixed concentrations, the tunable energy transfer efficiency is achieved based on the composite of mixed quantum dots and elastomeric film by utilizing the inherent nature of the flexibility of elastomeric film. To demonstrate our working principle, the composite of mixed-size CdSe quantum dots and poly-dimethylsiloxane has been studied. The results clearly show that the energy transfer process between proximal quantum dots follows the Förster resonance energy transfer, in which the dependence of the transfer efficiency E as a function of the donor-acceptor distance R obeys E=1∕[1+(R∕R0)6].
Isotope-ratio measurements reveal a young Moon
Authors: Wilson Mark
Published: February 2008

An analysis of lunar metals indicates that the Moon formed later than previously thought—after Earth’s core had separated from its mantle.
Semiconductor industry switches to hafnium-based transistors
Authors: Matthews Jermey N. A.
Published: February 2008

Plagued by quantum tunneling of charge carriers through gate insulators, chip manufacturers are shifting to high-dielectric-constant materials that maintain sufficient capacitance and reduce power leaks.
Magnetic monitoring of earth and space
Authors: Love Jeffrey J.
Published: February 2008

With data provided by magnetic observatories, geophysicists can gain insights into our planet’s interior and nearby space environment without even leaving the ground.
How to measure earth’s magnetic field
Authors: Auster Hans-Ulrich
Published: February 2008

Electromagnetic induction and spin precession are the key concepts behind the two devices most commonly used to determine geomagnetic fields.
Managing climate risks in Australia: options for water policy and irrigation management
Authors: Khan Shahbaz
Published: February 2008

Australia, a country which suffers from recurrent droughts, is currently experiencing a shift in climate. It is often classified as the driest inhabited continent due to the extremely low annual average rainfall (465 mm) and associated low annual average runoff (57 mm). This has required a regular revision of Australia’s water policy to align with the needs of its society. Several changes in water policy have been formulated in recent times with the objective of striking a balance between the consumptive and environmental components of flows in Australian catchments. Some of the developments that affect irrigated agriculture include: (i) the Council of Australian Government’s water reforms; (ii) the Murray–Darling Basin Commission cap (the volume of water that could be diverted under 1993–94 levels of development); (iii) environmental flow rules; and (iv) the National Water Initiative.
At a strategic level global climate change threatens the viability of irrigated agriculture and other industries. Under the present water reforms, longer-term water security is not guaranteed because these reforms do not explicitly take into account threats to water quantity and quality due to enhanced climate variability and change. At an operational level, current water allocation systems do not take into account state-of-the-art climate forecasting methods. Therefore, it is often not until after the irrigation season is well underway that irrigators have a reasonable knowledge of how much water will be available. Thus, there is considerable risk associated with planting and crop establishment decisions, resulting in a need for climate forecasting tools aimed at risk management. There is also a need for Australian water legislation and policy to be revisited to incorporate climate change and adaptive management options.
The Pythium - Fusarium root disease complex - an emerging constraint to irrigated maize in southern New South Wales
Authors: Harvey P. R. , Warren R. A. , Wakelin S.
Published: February 2008

A pathogen-selective fungicide trial was established at a site with a history of continuous maize cultivation with stubble retention to assess the impacts of Pythium, Fusarium and Rhizoctonia root diseases on maize productivity. High soilborne populations of Pythium and Fusarium were detected at sowing, with no significant differences in their distributions across the site. Significant increases in Fusarium and Pythium isolates were recovered from maize rhizosphere soils after the first 12 weeks of crop growth. While no isolates of phytopathogenic Rhizoctonia were recovered from soil or maize roots, 63 and 100% of roots examined were colonised by Pythium and Fusarium spp., respectively. Fungicides were, therefore, ineffective in suppressing rhizosphere fungal populations and inhibiting root infection and disease development. As a result, there were no significant increases in crop establishment, early crop growth (biomass) or grain yields with any of the pathogen-selective treatments. DNA sequencing identified six Pythium and five Fusarium spp. from infected maize roots (internal transcribed spacer 5.8s rDNA) and rhizosphere soils (rDNA and translation elongation factor-1α). These species have previously been reported as saprophytes on crop residues and as components of a root-disease complex contributing to seedling damping-off and root and stem rots of maize. Growth responses of rotation crops grown in natural and sterilised continuous maize soil indicated that soilborne root pathogens significantly reduced biomass production of maize and wheat, but not Adzuki bean and canola. Fungal isolation frequencies from these crops implied host-mediated selection of Pythium but not Fusarium spp., the former showing a preference for and greater pathogenicity towards maize and wheat.
Evaluation of strategies for increasing irrigation water productivity of maize in southern New South Wales using the MaizeMan model
Authors: Humphreys E. , White R. J. G. , Smith D. J. , Godwin D. C.
Published: February 2008

MaizeMan is Windows-based decision support software, derived from CERES Maize and SWAGMAN Destiny, which can be used for real-time irrigation scheduling or strategic analysis. Evaluation of MaizeMan for sprinkler and furrow-irrigated maize (Pioneer 3153) showed good predictive ability for yield, biomass, runoff and soil water depletion between sowing and harvest. MaizeMan simulations using 43 years of weather data from Griffith, New South Wales, suggested that the biggest influence on yield, irrigation requirement and irrigation water productivity is seasonal weather conditions. For example, yield of October-sown 3153 irrigated frequently to avoid soil water deficit varied from about 8 to 16 t/ha, while net irrigation and net irrigation water productivity varied from 7 to 11 ML/ha and 0.8 to 1.6 t/ML, respectively. The optimum sowing window for maximising yield and irrigation water productivity is wide, from late September to mid November. Delaying sowing beyond this may result in higher yield and irrigation water productivity; however, delayed maturity would lead to problems for grain drying and harvesting in winter and increased insect pressure. The simplest management strategy for maximising yield and irrigation water productivity is irrigation scheduling tailored to soil type. Irrigation scheduling can be assisted by real-time scheduling using MaizeMan, provided soil hydraulic properties are accurately characterised. One to two irrigations can also be saved by growing shorter duration hybrids, but the tradeoff is lower yield, while irrigation water productivity is maintained. Simulated sprinkler irrigation increased yield and net irrigation water productivity by small amounts (averages of 0.5 t/ha and 0.2 t/ML, respectively) relative to well-scheduled flood irrigation, through improved soil water and aeration status and reduced deep drainage loss.
Maize productivity in southern New South Wales under furrow and pressurised irrigation
Authors: O'Neill C. J. , Humphreys E. , Louis J. , Katupitiya A.
Published: February 2008

Irrigation farmers in the Murray–Darling Basin of Australia are under considerable pressure to reduce the amount of water they use for irrigation, while sustaining production and profitability. Changing from surface to pressurised irrigation systems may provide some or all of these outcomes; however, little is known about the performance of alternative irrigation methods for broadacre annual crops in this region. Therefore, a demonstration site for comparing furrow, subsurface drip and sprinkler irrigation was established on a representative clay soil in the Coleambally Irrigation Area, NSW. The performance of maize (Zea mays L.) under the three irrigation systems was compared during the 2004–05 season. Subsurface drip irrigated maize out-performed sprinkler and furrow irrigated maize in terms of grain yield (drip 11.8 t/ha, sprinkler 10.5 t/ha, furrow 10.1 t/ha at 14% moisture), net irrigation water application (drip 5.1 ML/ha, sprinkler 6.2 ML/ha, furrow 5.3 ML/ha), net irrigation water productivity (drip 2.3 t/ML, sprinkler 1.7 t/ML, furrow 1.9 t/ML) and total water productivity (drip 1.7 t/ML, sprinkler 1.4 t/ML, furrow 1.3 t/ML). Thus, subsurface drip irrigation saved ~30% of the total amount of water (irrigation, rain, soil water) needed to produce the same quantity of grain using furrow irrigation, while sprinkler irrigation saved ~8% of the water used. The higher net irrigation with sprinkler irrigation was largely due to the lower soil water content in the sprinkler block at the time of sowing. An EM31 survey indicated considerable spatial soil variability within each irrigation block, and all irrigation systems had spatially variable water distribution. Yield variability was very high within all irrigation systems, and appeared to be more strongly associated with irrigation variability than soil variability. All irrigation blocks had large patches of early senescence and poor cob fill, which appeared to be due to nitrogen and/or water deficit stress. We expect that crop performance under all irrigation systems can be improved by improving irrigation, soil and N management.