bluuebunny/crossref_metadata_2025 huggingface dataset:
The NOAA nitrous oxide standard scale for atmospheric observations
Authors: Hall B. D. , Dutton G. S. , Elkins J. W.
Published: May 2007

A new nitrous oxide (N2O) calibration scale has been developed for atmospheric observations. The NOAA‐2006 N2O scale is based on gravimetrically prepared compressed gas standards. This scale supercedes the NOAA‐2000 scale, which was accepted by the community of experts within the World Meteorological Organization Global Atmosphere Watch program (GAW) as the GAW reference standard. The new scale is defined by thirteen “daughter” standards with dry air mole fractions ranging from 261–371 parts‐per‐billion (nmol mol−1, ppb). These were derived from four part‐per‐million (mmol mol−1, ppm) level “parents”. Standards were evaluated using gas chromatography with electron capture detection. The daughter standards are internally consistent with a standard deviation of residuals of 0.33 ppb, and there is essentially no detectable difference among “cousins” (standards prepared from different parents). The NOAA‐2006 scale is 0.19 ppb lower than the NOAA‐2000 scale at 320 ppb. The global mean N2O mixing ratio (dry air mole fraction), calculated from in situ observations at five monitoring sites was 318.46 ppb in 2004 on the new scale. The NOAA‐2006 scale compares well with other scales based on comparisons of compressed gas standards. The NOAA‐2006 scale is, on average, 0.23% higher than that defined by NIST Standard Reference Materials 2608 and 2609, and an average of 0.01% lower than the Scripps Institution of Oceanography SIO‐98 scale over the range 298–319 ppb.
Stress associated coda attenuation from ultrasonic waveform measurements
Authors: Guo Meng‐Qiu , Fu Li‐Yun
Published: May 2007

The theoretical and practical exploration of stress changes from seismic waves has been the focus of recent debate within the scientific community because of its direct implications on earthquake forecasts and seismic hazards. Propagating in underground structures, wave velocity and attenuation contain information on stress changes of the Earth's interior as a result of changes in the physical state of materials. Seismic coda, which consists of a superposition of incoherent scattered waves, is known to reflect small‐scale random heterogeneities in the earth medium. In this article, we investigate the coda attenuation under different effective stresses using laboratory measurements to increase our understanding of the dependence of acoustic‐coda attenuation on stress variations in rocks.
Mapping ferromagnetism in Ti1−xCoxO2: Role of preparation temperature (200–900°C) and doping concentration (0.00015⩽x⩽0.1)
Authors: Reddy K. M. , Punnoose A.
Published: May 2007

Based on the conflicting reports in the literature, an extensive investigation to map room-temperature ferromagnetic regimes in the Ti1−xCoxO2 system has been undertaken by studying 70 different sol-gel synthesized nanopowder samples by systematically varying x and/or annealing temperatures TA in the 0.00015⩽x⩽0.1 and 200–900°C ranges, respectively. The evolved map demonstrates interesting roles of x and TA resulting in localized regions and pockets of ferromagnetic behavior (⩽0.32μB) which changes gradually to larger nonferromagnetic regions. In general, the ferromagnetic regimes occur at higher Co concentrations as TA increases. X-ray diffraction studies showed a gradual decrease in temperature range at which the anatase-to-rutile transformation occurs in Ti1−xCoxO2 as x increased from 0 to 0.1. Co doping also lowered the band gap energy.
Fine pole-pitch magnetizing method for Nd–Fe–B isotropic magnet with high coercivity
Authors: Komura H. , Kitaoka M. , Kiyomiya T. , Matsuo Y.
Published: May 2007

Fine pole-pitch magnetization of Nd–Fe–B magnets is an important technology that contributes to miniaturization of electromagnetic devices and smaller fractional movement. However, as Nd–Fe–B magnets have a high coercivity, large amounts of energy are required for magnetization. Miniaturization of devices is associated with insufficient magnetization characteristics due to the limitations of current density. We developed a magnetization method using heating system. This method involves cooling in the magnetizing field by permanent magnets after rapid heating to temperatures above the Curie point of the Nd–Fe–B magnet. This method, which we named “ultra high magnetizing (UHM) process,” achieved greater magnetization characteristics than conventional technology. Therefore, the UHM process is a useful technology to achieve further miniaturization of electromagnetic devices.
Magnetoacoustic properties of self-biased Terfenol-D 2-2 composites
Authors: Garcia-Gancedo L. , Busbridge S. C. , Pernod P. , Preobrazhensky V.
Published: May 2007

Self-biased Terfenol-D 2-2 composites exhibit high frequency of actuation and good magnetomechanical properties; however, their potential usefulness is highly dependent on their magnetoacoustic properties, particularly for ultrasonic applications. The speed of sound, c, and its variation with an externally applied magnetic field have been measured for the above composites using a 10MHz longitudinal pulse. When the sound propagates parallel to the layers, the acoustic impedance was found to be independent of the external applied field, and lower than that for bulk Terfenol-D. The magnetomechanical coupling coefficient was found to be generally low (up to 0.35) and dependent on the volume ratio of materials, being higher for the specimens with greater content of Terfenol-D. The low attenuation, low acoustic impedance, and high frequency of actuation make this structure an interesting alternative for use in underwater∕sound navigation and ranging and other ultrasonic applications. When the pulse propagates orthogonal to the layers, c was found to vary by up to 3% with the application of an external field, but the acoustic attenuation was found to be very high due to the multiple reflections produced at the interfaces between the layers. This latter phenomenon has been calculated theoretically.
Combined time-resolved x-ray magnetic circular dichroism and ferromagnetic resonance studies of magnetic alloys and multilayers (invited)
Authors: Arena D. A. , Vescovo E. , Kao C.-C. , Guan Y. , Bailey W. E.
Published: May 2007

We present measurements of element- and time-resolved ferromagnetic resonance (FMR) in magnetic thin films at gigahertz frequencies via an implementation of time-resolved x-ray magnetic circular dichroism (TR-XMCD). By combining TR-XMCD and FMR, using a rf excitation that is phase locked to the photon bunch clock, the dynamic response of individual layers or precession of individual elements in an alloy can be measured. The technique also provides extremely accurate measurements of the precession cone angle (to 0.1°) and the phase of oscillation (to 2°, or ∼5ps at 2.3GHz). TR-XMCD combined with FMR can be used to study the origins of precessional damping by measuring the relative phase of dissimilar precessing magnetic moments. We have used the technique to measure the response of specific elements and separate layers in several alloys and structures, including a single Ni81Fe19 layer, a pseudo-spin-valve structure (Ni81Fe19∕Cu∕Co93Zr7), magnetic bilayers consisting of low damping (Co93Zr7) and high damping (Tb-doped Ni81Fe19) layers joined across a common interface, and elemental moments in Tb-doped Ni81Fe19.
Magnetocaloric properties of Fe and Ge doped Ni2Mn1−xCuxGa
Authors: Khan Mahmud , Stadler Shane , Ali Naushad
Published: May 2007

The magnetocaloric properties of Fe and Ge doped Ni2Mn0.75Cu0.25Ga Heusler alloys have been investigated. Using Ni2Mn0.75Cu0.25Ga as the parent material, the Fe doped system (Ni2Mn1−x(Cu–Fe)xGa) and a Ge doped system (Ni2Mn1−xCuxGa1−xGex) were studied. The manipulation of the Mn–Cu subsystem with Fe doping results in a decrease of the first order magnetostructural transition temperature, whereas the substitution of Ge for the Mn–Cu–Ga subsystems results in an increase of the magnetostructural transition temperature. In both cases the giant magnetocaloric effect is successfully preserved.
Brief rapid thermal treatment effect on patterned CoFeB-based magnetic tunneling junctions
Authors: Wu Kuo-Ming , Huang Chao-Hsien , Wang Yung-Hung , Kao Ming-Jer , Tsai Ming-Jinn , Wu Jong-Ching , Horng Lance
Published: May 2007

The brief thermal treatment effects on the magnetoresistance of microstructured Co60Fe20B20-based magnetic tunneling junctions have been studied. The elliptical shape of devices with long/short axis of 4∕2μm was patterned out of film stack of seed layer (20)∕PtMn(15)∕Co60Fe20B20(3)∕Al(0.7)oxide∕C60Fe20B20(20)∕capping layer (48) (thickness unit in nanometers) combining conventional lithography and inductively coupled plasma reactive ion beam etching technologies. The thermal annealing was carried out with device loading into a furnace with preset temperatures ranging from 100to400°C for only 5min in the absence of any external magnetic field. The magnetoresistance was found to increase with increasing annealing temperatures up to 250°C and then decrease at higher annealing temperatures. In addition, the magnetoresistance ratio of around 35%, similar to that of as-fabricated devices, sustains up to annealing temperature of 350°C. This survival of magnetoresistance at higher annealing temperature is due to boron conservation in the amorphous CoFeB ferromagnetic layer at higher annealing temperature for only a short time, which is manifested using x-ray diffractometer technique.
Coupled precession modes in indirect exchange-coupled [Pt∕Co]–Co thin films
Authors: Michalski Steven , Zhou Jian , Skomski Ralph , Kirby Roger D.
Published: May 2007

Magneto-optical measurements are used to investigate Pt–Co and Co layers exchange-coupled by a Pt layer. The magnetization precession was measured in a pump-probe experiment using a femtosecond laser with direct optical excitation. The competing magnetic anisotropies of the layers yield a noncollinear spin structure with a field-dependent angle between the layers. Two modes, a ferromagnetic or “acoustic” mode and an antiferromagnetic or “optic” mode, are identified from the Fourier-transformed excitation spectra, and the obtained line positions are used to estimate the interlayer exchange constants.
Properties of vortex propagation in a niobium film with spacing-graded density of pinning sites
Authors: Horng Lance , Wu T. C. , Wu J. C. , Cao R. , Yang T. J.
Published: May 2007

The vortex propagation has been investigated in Nb superconductors with one dimension spacing-graded density of submicrometer-scaled holes in this research. A rectification effect can be discerned because the applied ac is transformed into a net dc voltage. These results demonstrate that the rectification is mainly characterized by the asymmetric pinning landscape and the rectified voltage depends considerably on temperature and the amplitude of applied ac. The dc voltage increases steeply up to the maximum value and then decreases to zero dc voltage with the increase of ac. The shape of peaks in the dc voltage signal become steeper and move to higher applied ac regime with the decrease of temperature.
Crystallographic and Mössbauer studies of Li0.5Fe2.5O4 prepared by high temperature thermal decomposition and sol-gel methods
Authors: Hyun Sung Wook , Kim Chul Sung
Published: May 2007

Li 0.5 Fe 2.5 O 4 powders were prepared by high temperature thermal decomposition (HTTD) and sol-gel methods. The sample prepared by HTTD method (SA) has space group of Fd3m. The samples annealed at 700°C (SB) and quenched at 1000°C (SC) prepared by sol-gel method have space groups of P4332 and Fd3m, respectively. The saturation magnetizations (Ms) for the sample prepared by HTTD method (SA) at room temperature is 55emu∕g and those for the samples annealed at 700°C (SB) and quenched at 1000°C (SC) prepared by sol-gel method are 59 and 62emu∕g, respectively. In contrast, the coercivity (Hc) values of the each sample are 4.1, 93.7, and 9.1Oe, respectively. Mössbauer spectra of each sample have been obtained from 4.2to700K. The valence state of Fe ions for the tetrahedral (A) and octahedral (B) sites is Fe3+. Mössbauer spectrum of the sample prepared by HTTD method shows superparamagnetic behavior at room temperature, while in case of sol-gel method, Mössbauer spectra show ferrimagnetic state of six line having the hyperfine field (Hf) values of 518kOe for the A sites and 536kOe for the B sites.
Optimization of magneto-optical response of FeF2∕Fe∕FeF2 sandwiches for microwave field detection
Authors: Lopusnik Radek , Correu James , Harward Ian , Widuch Stefania , Maślankiewicz Paweł , Demirtas Sezen , Celinski Zbigniew , Liskova Eva , Veis Martin , Visnovsky Stefan
Published: May 2007

We report on optimizing the magneto-optical (MO) response of dielectric/Fe/dielectric sandwich structures for microwave B-field sensor applications. We have performed experimental MO spectroscopic and simulation studies of FeF2∕Fe∕FeF2 sandwiches with varying both top and bottom FeF2 layer thicknesses. We evaluate the performance of the sensor with MO figure of merit (off-diagonal reflection coefficient) rather than with MO polarization state (MO azimuth rotation and ellipticity). Our simulations indicate that an increase in the modulus of the MO signal by a factor of 17 is feasible compared to the bulk Fe. However, the corresponding enhancement of the figure of merit, which is the relevant parameter, is only threefold. These simulations were carried out for the operating wavelength of sensors at 810nm. We show, contrary to the general belief, that in order to enhance the MO performance of the sensor it is more important to optimize the bottom dielectric layer rather than the top layer.
Wave packet theory of dynamic stimulated Raman spectra in femtosecond pump-probe spectroscopy
Authors: Sun Zhigang , Jin Zhongqi , Lu J. , Zhang Dong H. , Lee Soo-Y.
Published: May 2007

The quantum theory for stimulated Raman spectroscopy from a moving wave packet using the third-order density matrix and polarization is derived. The theory applies, in particular, to the new technique of femtosecond broadband stimulated Raman spectroscopy (FSRS). In the general case, a femtosecond actinic pump pulse first prepares a moving wave packet on an excited state surface which is then interrogated with a coupled pair of picosecond Raman pump pulse and a femtosecond Raman probe pulse and the Raman gain in the direction of the probe pulse is measured. It is shown that the third-order polarization in the time domain, whose Fourier transform governs the Raman gain, is given simply by the overlap of a first-order wave packet created by the Raman pump on the upper electronic state with a second-order wave packet on the initial electronic state that is created by the coupling of the Raman pump and probe fields acting on the molecule. Calculations are performed on model potentials to illustrate and interpret the FSRS spectra.
Scaling of fracture energy in tensile debonding of viscoelastic films
Authors: Seshadri Muralidhar , Saigal Sunil , Jagota Anand , Bennison Stephen J.
Published: May 2007

The work done to separate viscoelastic adherends is often dominated by energy dissipation due to the bulk deformation that accompanies the intrinsic processes of interfacial separation. The inter-relationship between bulk and interfacial deformation processes is studied here by analyzing a one-dimensional model for steady-state crack propagation between a rigid substrate and a thin viscoelastic film when the latter is subjected to tensile loading and the former is fixed. The viscoelastic layer is represented by a standard linear solid and is connected to the rigid substrate via a Dugdale cohesive zone model. The principal result of the analysis is a prediction for the dependence of the total work of fracture on the rate of loading. A threshold crack-tip velocity that governs the onset of dissipation is determined as a function of the film thickness and the interfacial and viscoelastic parameters of the film. Based on the ratio of the crack-tip velocity to the threshold velocity, three velocity regimes are identified where the energy dissipation is low, high, or intermediate. These correspond, respectively, to the overlap of the cohesive zone with the film material that is completely relaxed, is completely unrelaxed, or is in the process of relaxation. An approximate solution for the scaling of fracture energy in these three regimes has been presented. Finally, the relevance of these results to a two-dimensional problem is discussed.
Calculation of argon trimer rovibrational spectrum
Authors: Karlický František , Lepetit Bruno , Kalus René , Gadéa Florent Xavier
Published: May 2007

Rovibrational spectra of Ar3 are computed for total angular momenta up to J=6 using row-orthonormal hyperspherical coordinates and an expansion of the wave function on hyperspherical harmonics. The sensitivity of the spectra to the two-body potential and to the three-body corrections is analyzed. First, the best available semiempirical pair potential (HFDID1) is compared with our recent ab initio two-body potential. The ab initio vibrational energies are typically 1–2cm−1 higher than the semiempirical ones, which is related to the slightly larger dissociation energy of the semiempirical potential. Then, the Axilrod-Teller asymptotic expansion of the three-body correction is compared with our newly developed ab initio three-body potential. The difference is found smaller than 0.3cm−1. In addition, we define approximate quantum numbers to describe the vibration and rotation of the system. The vibration is represented by a hyper-radial mode and a two-degree-of-freedom hyperangular mode, including a vibrational angular momentum defined in an Eckart frame. The rotation is described by the total angular momentum quantum number, its projection on the axis perpendicular to the molecular plane, and a hyperangular internal momentum quantum number, related to the vibrational angular momentum by a transformation between Eckart and principal-axes-of-inertia frames. These quantum numbers provide a qualitative understanding of the spectra and, in particular, of the impact of the nuclear permutational symmetry of the system (bosonic with zero nuclear spin). Rotational constants are extracted from the spectra and are shown to be accurate only for the ground hyperangular mode.
Transport properties of d-electron-based transparent conducting oxide: Anatase Ti1−xNbxO2
Authors: Furubayashi Yutaka , Yamada Naoomi , Hirose Yasushi , Yamamoto Yukio , Otani Makoto , Hitosugi Taro , Shimada Toshihiro , Hasegawa Tetsuya
Published: May 2007

The transport properties of a d-electron-based transparent conducting oxide, Nb-doped anatase Ti1−xNbxO2, were investigated as a function of the Nb content x. From optical resistivity spectra, the static effective mass was evaluated to be ∼0.4m0 in the low-carrier-concentration (ne) regime, which is approximately the same as those of conventional transparent conducting oxides (TCOs), and two orders of magnitude smaller than that reported for rutile TiO2. The Hall mobility at room temperature, which is maximized at around x=0.01 (ne∼1021cm−3), was found to be mainly dominated by optical phonon scattering unlike that of other TCOs.
Structural and functional characterization of (110)-oriented epitaxial La2∕3Ca1∕3MnO3 electrodes and SrTiO3 tunnel barriers
Authors: Infante I. C. , Sánchez F. , Fontcuberta J. , Fusil S. , Bouzehouane K. , Herranz G. , Barthélémy A. , Estradé S. , Arbiol J. , Peiró F. , Mossanek R. J. O. , Abbate M. , Wojcik M.
Published: May 2007

La 2 ∕ 3 Ca 1 ∕ 3 MnO 3 (LCMO) films have been deposited on (110)-oriented SrTiO3 (STO) substrates. X-ray diffraction and high-resolution electron microscopy reveal that the (110) LCMO films are epitaxial and anisotropically in-plane strained, with higher relaxation along the [1–10] direction than along the [001] direction; x-ray absorption spectroscopy data signaled the existence of a single intermediate Mn3+∕4+ 3d-state at the film surface. Their magnetic properties are compared to those of (001) LCMO films grown simultaneously on (001) STO substrates It is found that (110) LCMO films present a higher Curie temperature (TC) and a weaker decay of magnetization when approaching TC than their (001) LCMO counterparts. These improved films have been subsequently covered by nanometric STO layers. Conducting atomic-force experiments have shown that STO layers, as thin as 0.8 nm, grown on top of the (110) LCMO electrode, display good insulating properties. We will show that the electric conductance across (110) STO layers, exponentially depending on the barrier thickness, is tunnel-like. The barrier height in STO (110) is found to be similar to that of STO (001). These results show that the (110) LCMO electrodes can be better electrodes than (001) LCMO for magnetic tunnel junctions, and that (110) STO are suitable insulating barriers.
Design of UV laser pulses for the preparation of matrix isolated homonuclear diatomic molecules in selective vibrational superposition states
Authors: Korolkov M. V. , Manz J.
Published: May 2007

The preparation of matrix isolated homonuclear diatomic molecules in a vibrational superposition state c0∙Φe=1,v=0+cj∙Φe=1,v=j, with large (∣c0∣2≈1) plus small contributions (∣cj∣2⪡1) of the ground v=0 and specific v=j low excited vibrational eigenstates, respectively, in the electronic ground (e=1) state, and without any net population transfer to electronic excited (e>1) states, is an important challenge; it serves as a prerequisite for coherent spin control. For this purpose, the authors investigate two scenarios of laser pulse control, involving sequential or intrapulse pump- and dump-type transitions via excited vibronic states Φex,k with a dominant singlet or triplet character. The mechanisms are demonstrated by means of quantum simulations for representative nuclear wave packets on coupled potential energy surfaces, using as an example a one-dimensional model for Cl2 in an Ar matrix. A simple three-state model (including Φ1,0, Φ1,j and Φex,k) allows illuminating analyses and efficient determinations of the parameters of the laser pulses based on the values of the transition energies and dipole couplings of the transient state which are derived from the absorption spectra.
Mitigation of electron attachment to oxygen in high pressure air plasmas by vibrational excitation
Authors: Frederickson K. , Lee W. , Palm P. , Adamovich I. V. , Rich J. W. , Lempert W. R.
Published: May 2007

A series of time resolved microwave attenuation measurements are performed of the electron number density of an electron beam generated, CO laser excited nonequilibrium O2∕N2 plasma. Resonant absorption of infrared radiation from the CO laser produces the nonequilibrium state, in which the heavy species vibrational modes are disproportionately excited, compared to the rotational and translational modes (Tvib≈2000–3000K vs TR∕T≈300K). It is shown that this results in an increase in the plasma free electron lifetime by two orders of magnitude compared to the unexcited cold gas, an effect which is ascribed to complete mitigation of rapid three-body electron attachment to molecular oxygen. A series of heavy species filtered pure rotational Raman scattering measurements are also presented, which exhibit minimal temperature change (+50K), indicating that the observed lifetime increase cannot be due to heavy-species thermal effects. Finally, computational modeling results infer an increase in the rate of O2− detachment by four to five orders of magnitude, compared to the equilibrium value.
A ternary nucleation model for the nucleation pathway of protein folding
Authors: Djikaev Y. S. , Ruckenstein Eli
Published: May 2007

Recently [Y. S. Djikaev and E. Ruckenstein, J. Phys. Chem. B 111, 886 (2007)], the authors proposed a kinetic model for the nucleation mechanism of protein folding where a protein was modeled as a heteropolymer consisting of hydrophobic and hydrophilic beads and the composition of the growing cluster of protein residues was assumed to be constant and equal to the overall protein composition. Here, they further develop the model by considering a protein as a three-component heteropolymer and by allowing the composition of the growing cluster of protein residues to vary independently of the overall one. All the bonds in the heteropolymer (now consisting of hydrophobic, hydrophilic, and neutral beads) have the same constant length, and all the bond angles are equal and fixed. As a crucial idea of the model, an overall potential around the cluster wherein a residue performs a chaotic motion is considered to be a combination of the average dihedral and average pairwise potentials assigned to the bead. The overall potential as a function of the distance from the cluster center has a double well shape which allows one to determine its emission and absorption rates by using a first passage time analysis. Knowing these rates as functions of three independent variables of a ternary cluster, one can develop a self-consistent kinetic theory for the nucleation mechanism of folding of a protein using a ternary nucleation formalism and evaluate the size and composition of the nucleus and the protein folding time. As an illustration, the model is applied to the folding of bovine pancreatic ribonuclease consisting of 124 amino acids whereof 40 are hydrophobic, 81 hydrophilic, and 3 neutral. With a reasonable choice of diffusion coefficients of the residues in the native state and potential parameters, the model predicts folding times in the range of 1–100s.
Relativistic calculation of nuclear magnetic shielding tensor using the regular approximation to the normalized elimination of the small component. II. Consideration of perturbations in the metric operator
Authors: Maeda H. , Ootani Y. , Fukui H.
Published: May 2007

A previous relativistic shielding calculation theory based on the regular approximation to the normalized elimination of the small component approach is improved by the inclusion of the magnetic interaction term contained in the metric operator. In order to consider effects of the metric perturbation, the self-consistent perturbation theory is used for the case of perturbation-dependent overlap integrals. The calculation results show that the second-order regular approximation results obtained for the isotropic shielding constants of halogen nuclei are well improved by the inclusion of the metric perturbation to reproduce the fully relativistic four-component Dirac-Hartree-Fock results. However, it is shown that the metric perturbation hardly or does not affect the anisotropy of the halogen shielding tensors and the proton magnetic shieldings.
Self-consistent-field method and τ-functional method on group manifold in soliton theory. II. Laurent coefficients of soliton solutions for sl̂n and for sûn
Authors: Nishiyama Seiya , da Providência João , Komatsu Takao
Published: May 2007

To go beyond perturbative method in terms of variables of collective motion, using infinite-dimensional fermions, we have aimed to construct the self-consistent-field (SCF) theory, i.e., time dependent Hartree-Fock theory on associative affine Kac-Moody algebras along the soliton theory. In this paper, toward such an ultimate goal we will reconstruct a theoretical frame for a υ (external parameter)-dependent SCF method to describe more precisely the dynamics on the infinite-dimensional fermion Fock space. An infinite-dimensional fermion operator is introduced through Laurent expansion of finite-dimensional fermion operators with respect to degrees of freedom of the fermions related to a υ-dependent and a Υ-periodic potential. As an illustration, we derive explicit expressions for the Laurent coefficients of soliton solutions for sl̂n and for sûn on infinite-dimensional Grassmannian. The associative affine Kac-Moody algebras play a crucial role to determine the dynamics on the infinite-dimensional fermion Fock space.
Microwave shielding of transparent and conducting single-walled carbon nanotube films
Authors: Xu Hua , Anlage Steven M. , Hu Liangbing , Gruner George
Published: May 2007

The authors measured the transport properties of single-walled carbon nanotube (SWCNT) films in the microwave frequency range from 10MHzto30GHz by using the Corbino reflection technique from temperatures of 20–400K. Based on the real and imaginary parts of the microwave conductivity, they calculated the shielding effectiveness for various film thicknesses. Shielding effectiveness of 43dB at 10MHz and 28dB at 10GHz are found for films with 90% optical transmittance, which suggests that SWCNT films are promising as a type of transparent microwave shielding material. By combining their data with those from the literature, the conductivity of SWCNT films was established in a broad frequency range from dc to visible.
Switchable two-color electroluminescence based on a Si metal-oxide-semiconductor structure doped with Eu
Authors: Prucnal S. , Sun J. M. , Skorupa W. , Helm M.
Published: May 2007

A Si metal-oxide-semiconductor electroluminescent device structure is reported which emits two colors, while being doped with a single rare-earth element. Thermally grown SiO2 oxide layers were implanted with Eu and subseqently annealed. Depending on the electrical excitation current, the luminescence is red or blue, which can be ascribed to electronic transitions in tri- and divalent europium (Eu3+ and Eu2+), respectively.
Approach for three-dimensional observation of mesoscopic precipitates in alloys by coherent x-ray diffraction microscopy
Authors: Takahashi Yukio , Nishino Yoshinori , Ishikawa Tetsuya , Matsubara Eiichiro
Published: May 2007

An approach for evaluating three-dimensional spatial distribution of precipitates buried within a bulk alloy by coherent x-ray diffraction microscopy (CXDM) is proposed. In this study, the outer shape and the internal structure of the micrometer-sized sample in a precipitation-hardened aluminum alloy are observed by CXDM. A high-electron-density region resulting from precipitates is clearly visualized, implying that the precipitates distribute inhomogeneously in the Al matrix at several tens of nanometer scale. This is the important result toward in situ observation of the formation of internal structures in metallic materials on the nanomesoscale by CXDM with x-ray free electron lasers.
Linearly polarized dual-wavelength vertical-external-cavity surface-emitting laser
Authors: Fan Li , Fallahi Mahmoud , Hader Jörg , Zakharian Aramais R. , Moloney Jerome V. , Stolz Wolfgang , Koch Stephan W. , Bedford Robert , Murray James T.
Published: May 2007

The authors demonstrate the multiwatt linearly polarized dual-wavelength operation in an optically pumped vertical-external-cavity surface-emitting laser by means of an intracavity tilted Fabry-Perot etalon and a Brewster window. The sum frequency generation from the lithium triborate crystal pumped by this laser confirms that these two wavelengths oscillate simultaneously. Over 30dB side-mode suppression can be achieved at dual wavelengths with a spectral spacing of 2.1nm. The output power is slightly reduced by the intracavity Fabry-Perot etalon and Brewster window.
Nanocrystalline LaGaO3:Tm3+ as an efficient blue phosphor for field emission displays with high color purity
Authors: Liu Xiaoming , Lin Jun
Published: May 2007

Nanocrystalline Tm3+-doped LaGaO3 phosphors were prepared through a Pechini-type sol-gel process [M. P. Pechini, U.S. Patent No. 3,330,697 (11 July 1967)]. X-ray diffraction, field emission scanning electron microscopy, photoluminescence, and cathodoluminescence (CL) spectra were utilized to characterize the synthesized phosphors. Under the excitation of ultraviolet light and low voltage electron beams (0.5–3kV), the Tm3+-doped LaGaO3 phosphors show the characteristic emissions from the LaGaO3 host lattice and the Tm3+ (D21, G41-F43, and H63 transitions), respectively. The blue CL of the Tm3+-doped LaGaO3 phosphors, with a dominant wavelength of 458nm, had better Commission International I’Eclairage chromaticity coordinates (0.1552, 0.0630) and higher emission intensity than the commercial product (Y2SiO5:Ce3+).
Enhancing photon harvesting in organic solar cells with luminescent concentrators
Authors: Koeppe R. , Sariciftci N. S. , Büchtemann A.
Published: May 2007

The authors report on the application of luminescent concentrators on organic solar cells fabricated zinc-phthalocyanine and C60. These solar cells have their main absorption in the wavelength range between 600 and 800nm. Below 600nm, the low absorption limits the quantum efficiency. Luminescence concentrators are used to overcome this limitation by spectrally shifting blue and green light towards the red and waveguiding it to the solar cell. With a second solar cell harvesting the red light transmitted through the concentrator, the photocurrent density is increased compared to a single solar cell of equal active area from about 8.5 up to 10mA∕cm2.
Optimizing 13.5nm laser-produced tin plasma emission as a function of laser wavelength
Authors: White J. , Dunne P. , Hayden P. , O’Reilly F. , O’Sullivan G.
Published: May 2007

Extreme ultraviolet lithography requires a light source at 13.5nm to match the proposed multilayer optics reflectivity. The impact of wavelength and power density on the ion distribution and electron temperature in a laser-produced plasma is calculated for Nd:YAG and CO2 lasers. A steady-state figure of merit, calculated to optimize emission as a function of laser wavelength, shows an increase with a CO2 laser. The influence of reduced electron density in the CO2 laser-produced plasma is considered in a one-dimensional radiation transport model, where a more than twofold increase in conversion efficiency over that attainable with the Nd:YAG is predicted.
Determination of the epitaxial growth of zinc oxide nanowires on sapphire by grazing incidence synchrotron x-ray diffraction
Authors: Campos L. C. , Dalal S. H. , Baptista D. L. , Magalhães-Paniago R. , Ferlauto A. S. , Milne W. I. , Ladeira L. O. , Lacerda R. G.
Published: May 2007

This letter shows that aligned zinc oxide (ZnO) nanowires growth on sapphire substrates is epitaxial and demonstrates the crystallographic relation between the two using grazing incidence synchrotron x-ray diffraction (XRD). The in-plane lattice match between the sapphire and the nanowires was directly probed by using XRD at grazing angles of incidence, where the lattice match between the (0001) plane of the sapphire and the (11−20) plane of the ZnO were observed simultaneously. It will also be shown that gold acts as a catalyst to initiate ZnO nanowire growth, but it does not interfere with the epitaxial mechanism between the nanowires and the sapphire substrate.
X-ray diffraction reciprocal space mapping study of the thin film phase of pentacene
Authors: Yoshida Hiroyuki , Inaba Katsuhiko , Sato Naoki
Published: May 2007

The structure of the thin film phase of pentacene was investigated using x-ray diffraction reciprocal space mapping (RSM). The crystal structure was found to be triclinic with the following lattice parameters: a=0.593nm, b=0.756nm, c=1.565nm, α=98.6°, β=93.3°, and γ=89.8°. Atomic positions were determined by comparing the observed RSM diffraction intensities with theoretical calculations.
Experimental verification of a tunable optical negative refraction in nematic liquid crystals
Authors: Kang Lei , Zhao Qian , Li Bo , Zhou Ji , Zhu Hao
Published: May 2007

The authors experimentally demonstrate a magnetically tunable optical negative refraction (NR) in nematic liquid crystals (NLCs), arising from the variation of optical anisotropy in the NLCs induced by external magnetic field. By measuring the refraction angle of the transmitted beam through the prism-shaped NLC device, the tunable extraordinary refractions for different molecular directions using magnetic field are observed. It shows that NR in NLCs occurs at certain inclination angle and can be tuned by changing the direction of the magnetic field, which is in good agreement with the established theory.
Dielectric relaxation and ultrasonic attenuation of Sr4La2Ti4Nb6O30 tungsten bronze ceramics
Authors: Zhu Xiao Li , Chen Xiang Ming , Li Xiao Guang
Published: May 2007

Dielectric relaxation and ultrasonic attenuation spectra of Sr4La2Ti4Nb6O30 tungsten bronze ceramics were investigated over a broad temperature range. A broad permittivity peak with strong frequency dispersion was observed around 200K, which followed well the Vogel-Fulcher relationship, and is attributed to relaxor ferroelectric behavior with spin glass nature. The ultrasonic investigation provided further evidence on this thermally activated process, and both the dielectric relaxation and the freezing of polar clusters were clearly observed in the ultrasonic velocity shift and ultrasonic attenuation spectra.
Elastic interactions and diffusion of Sn in Si1−xGex systems
Authors: Riihimäki I. , Virtanen A. , Kettunen H. , Pusa P. , Laitinen P. , Räisänen J. , Collaboration the ISOLDE
Published: May 2007

Diffusion of Sn in relaxed Si1−xGex alloys has been studied systematically. In Si1−xGex, diffusion of Sn is faster than that of Si and Ge, and the results indicate that Sn diffusion in silicon and germanium is vacancy mediated. As Sn is isovalent, no long range Coulomb interactions exist between Sn atoms and native point defects. Since Sn atoms are larger than Si and Ge atoms, they cause stress in the SiGe lattice. The present findings are explained by attractive elastic interactions caused by pairing of Sn atoms with vacancies relaxing the stress and repulsive elastic interactions between Sn atoms and self-interstitials.
Highly efficient, tunable single photon source based on single molecules
Authors: Steiner Mathias , Hartschuh Achim , Korlacki Rafał , Meixner Alfred J.
Published: May 2007

The authors studied spatially isolated terrylene molecules immobilized in a quasiplanar optical λ∕2-microresonator using confocal microscopy and spectroscopy at variable temperatures. At T=1.8K, they observed individual molecules relaxing into microresonator-allowed vibronic levels of their electronic ground state by emission of single fluorescence photons. Coupling the purely electronic transition of embedded molecules to the longitudinal photonic mode of the microresonator resulted in an ultimate spectral narrowing and an increased collection efficiency of the emitted single photon wave trains.
Amphoteric arsenic in GaN
Authors: Wahl U. , Correia J. G. , Araújo J. P. , Rita E. , Soares J. C. ,   The ISOLDE Collaboration
Published: May 2007

The authors have determined the lattice location of implanted arsenic in GaN by means of conversion electron emission channeling from radioactive As73. They give direct evidence that As is an amphoteric impurity, thus settling the long-standing question as to whether it prefers cation or anion sites in GaN. The amphoteric character of As and the fact that AsGa “antisites” are not minority defects provide additional aspects to be taken into account for an explanantion of the so-called miscibility gap in ternary GaAs1−xNx compounds, which cannot be grown with a single phase for values of x in the range of 0.1<x<0.99.
Photorefractive star-shaped molecular glassy materials containing tricyanopyrroline-based chromophore
Authors: Jung Kyung Moon , Cho Min Ju , Jin Jung-Il , Choi Dong Hoon
Published: May 2007

The authors report the near-IR sensitive star-shaped molecule [D-(CBz-TCP)3] containing bifunctional chromophores. A nonlinear optical active tricyanopyrroline-based plasticizer was also synthesized and introduced into the prepared molecular glass so as to control the glass transi-tion temperature of the photorefractive matrix. In a doped glass, they observed significantly enhanced photorefractive performances with regard to the asymmetric energy transfer and the diffraction efficiency at 830nm. In the presence of a small amount of (2,4,7-trinitro-9- fluorenylidene)malononitrile, they could demonstrate a very large net two beam coupling gain higher than 300cm−1 and a diffraction efficiency of 58%.
Thin metal intracavity contact and lateral current-distribution scheme for GaN-based vertical-cavity lasers
Authors: Feezell D. F. , Farrell R. M. , Schmidt M. C. , Yamada H. , Ishida M. , DenBaars S. P. , Cohen D. A. , Nakamura S.
Published: May 2007

The authors report an effective lateral current-distribution scheme to achieve uniform hole injection in GaN-based vertical-cavity lasers. A thin (∼5nm) intracavity Pd∕Au layer is used to simultaneously achieve a low-resistance Ohmic contact and effective lateral current distribution across a circular injection aperture. Precise placement of a thin metal layer in a vertical-cavity laser is shown to yield negligible single-pass optical loss. Light-emitting diodes utilizing this intracavity contact and lateral current-distribution scheme are demonstrated, with effective lateral current distribution observed for aperture diameters up to 36μm. Continuous-wave operation at current densities exceeding 10kA∕cm2 is demonstrated.
Anisotropic acousto-optic diffraction by leaky wave radiation in ZX-LiNbO3
Authors: Rimeika R. , Čiplys D. , Každailis P. , Shur M. S.
Published: May 2007

The anisotropic light diffraction by bulk acoustic waves (BAWs) radiated by an interdigital transducer (IDT) operating at the leaky surface acoustic wave resonance in ZX-lithium niobate has been experimentally studied at an optical wavelength of 633nm in the range of acoustic frequencies from 35to190MHz. The possibility of optical probing of the IDT-radiated BAW properties is demonstrated. The experimentally determined values of the BAW propagation angle and velocity are 25° and 4050m∕s, respectively.
Characteristic boiling curve of carbon nanotube nanofluid as determined by the transient calorimeter technique
Authors: Xue H. S. , Fan J. R. , Hong R. H. , Hu Y. C.
Published: May 2007

Nickel-plated copper sphere is employed as the transient calorimeter to explore the boiling heat transfer characteristics of carbon nanotube (CNT) nanofluid. As compared to water, aqueous gum arabic (GA) solution has an enhanced critical heat flux (CHF), transition boiling, and minimum heat flux in film boiling (Leidenfrost point). CNT nanofluid has higher CHF than GA solution. Better wettability and deposits on the heating surface distort the characteristic boiling curve.
Interface effects in the magneto-optical properties of Co nanoparticles in dielectric matrix
Authors: Clavero C. , Armelles G. , Margueritat J. , Gonzalo J. , García del Muro M. , Labarta A. , Batlle X.
Published: May 2007

The authors present a study of the optical and magneto-optical properties of Co nanoparticles embedded in two amorphous dielectric matrices with different refractive indices such as ZrO2 and Al2O3. The nanostructured films were prepared by pulsed laser deposition, and the morphology and structure were studied by different characterization techniques. The optical and magneto-optical (MO) properties of the Co inside the nanoparticles differ from those of the bulk material; in particular, a decrease in the MO constants is found. These properties are found to depend on the nanoparticle size and on the dielectric matrix, due to the different nanoparticle-matrix interfaces appearing in both cases.
Annealing induced inversion of quantum dot fine-structure splitting
Authors: Margapoti E. , Worschech L. , Forchel A. , Tribu A. , Aichele T. , André R. , Kheng K.
Published: May 2007

By mapping the anisotropy fine-structure splitting of the exciton ground state in the luminescence spectra of individual CdxZn1−xSe quantum dots, treated by postgrowth rapid thermal annealing (TA), a preferred in-plane axis of Zn–Cd interdiffusion has been identified. In particular, a TA-induced sign reversal of the fine-structure splitting is demonstrated. Additionally, in the annealed quantum dots, the binding energy of the charged exciton reaches a maximum value when the fine-structure splitting is minimum. The studies demonstrate that by postgrowth thermal annealing the symmetry of individual quantum dot can be modulated.
Role of water adsorption in photoinduced superhydrophilicity on TiO2 thin films
Authors: Lee Fuk Kay , Andreatta Gaëlle , Benattar Jean-Jacques
Published: May 2007

The ultraviolet (UV) irradiation of a titanium dioxide (TiO2) film surface gives rise to two simultaneous phenomena: photocatalysis and superhydrophilicity. Photocatalysis has been thoroughly studied, but the mechanism governing superhydrophilicity remains controversial. The authors’ investigations show the effects induced by UV irradiation on the water adsorption and desorption on the TiO2 surface. The observations prove that superhydrophilicity cannot be solely induced by the removal of organic contamination via photocatalysis, but is associated with water adsorption most probably due to the appearance of hydroxyl groups on surface defects.
Rectification of radio frequency current in ferromagnetic nanowire
Authors: Yamaguchi A. , Miyajima H. , Ono T. , Suzuki Y. , Yuasa S. , Tulapurkar A. , Nakatani Y.
Published: May 2007

The authors report the rectification of a constant wave radio frequency (rf) current by using a single-layer magnetic nanowire; a direct-current voltage is resonantly generated when the rf current flows through the nanowire. The mechanism of the rectification is discussed in terms of the spin-torque diode effect reported for magnetic tunnel junction devices, and the rectification is shown to be directly attributable to resonant spin wave excitation by the rf current.
Engineering the quality factors of coupled-cavity modes in photonic crystal slabs
Authors: Fussell David P. , Dignam Marc M.
Published: May 2007

The authors present a tight-binding approach to calculating the quality factor, or Q, of the modes of coupled-cavity systems in photonic crystal slabs. They show how this approach can be used to engineer coupled-cavity waveguides and arrays so as to maximize the Q of the modes. Due to destructive interference of the out-of-plane radiation from individual cavities, the Q of some coupled-cavity modes can be much higher than the Q of the individual cavities. An array with as few as 25 coupled cavities can produce isolated modes with Qs more than an order of magnitude greater than the Q of the constituent cavities, providing an alternative approach to obtaining high-Q modes.
Vertical Disparity Affects Shape and Size Judgments across Surfaces Separated in Depth
Authors: O'Kane Lisa M , Hibbard Paul B
Published: May 2007

Vertical binocular disparity provides a useful source of information allowing three-dimensional (3-D) shape to be recovered from horizontal binocular disparity. In order to influence metric shape judgments, a large field of view is required, suggesting that vertical disparity may play a limited role in the perception of objects projecting small retinal images. This limitation could be overcome if vertical disparity information could be pooled over wide areas of 3-D space. This was investigated by assessing the effect of vertical disparity scaling of a large surround surface on the perceived size and 3-D shape of a small, central object. Observers adjusted the size and shape of a virtual, binocularly defined ellipsoid to match those of a real, hand-held tennis ball. The virtual ball was presented at three distances (200, 325, and 450 mm). Vertical disparities in a large surround surface were manipulated to be consistent with a distance of 160 mm or infinity. Both shape and size settings were influenced by this manipulation. This effect did not depend on presenting the surround and target objects at the same distance. These results suggest that the influence of vertical disparity on the perceived distance to a surface also affects the estimated distance of other visible surfaces. Vertical disparities are therefore important in the perception of metric depth, even for objects that in themselves subtend only small retinal images.