bluuebunny/crossref_metadata_2025 huggingface dataset:
Complementarity in biology
Authors: Mazzocchi Fulvio
Published: April 2010

Fulvio Mazzocchi asserts that neither systems nor reductionist approaches to the analysis of life are sufficient to understand the complexity of living things. Instead, biology should adopt a mindset in which different explanations for biological phenomena complement each other in a manner similar to the theoretical framework of quantum physics.
Membranes in motion
Authors: van Meer Gerrit
Published: April 2010

The Keystone Symposium on the Molecular Basis for Biological Membrane Organization and Dynamics held in January this year offered new insights into the molecular machines at work in cells. Topics included the machinery responsible for the dynamic shape of organelles, the budding and fusion of vesicular carriers, and the intricate sorting systems that ensure the correct delivery of cellular components.
Surface tension-driven chip self-assembly with load-free hydrogen fluoride-assisted direct bonding at room temperature for three-dimensional integrated circuits
Authors: Fukushima T. , Iwata E. , Konno T. , Bea J.-C. , Lee K.-W. , Tanaka T. , Koyanagi M.
Published: April 2010

We have demonstrated fluidic chip self-assembly on Si wafers for fabricating three-dimensional integrated circuits. In this self-assembly technique, small droplets of hydrofluoric acid were employed to simultaneously align many millimeter-scale chips and directly bond them to the hydrophilic bonding areas formed on the host wafers by oxide–oxide bonding. The liquid surface tension enables many Si chips to be self-assembled with the highest alignment accuracy of 50 nm. In addition, many chips were tightly bonded to the hydrophilic bonding areas without applying a mechanical force after the liquid was evaporated at room temperature.
Metastable γ-FeNi nanostructures with tunable Curie temperature
Authors: Miller K. J. , Sofman M. , McNerny K. , McHenry M. E.
Published: April 2010

We report on new metastable γ-FeNi nanoparticles produced by mechanical alloying of melt-spun ribbon using a high energy ball mill followed by a solution annealing treatment in the γ-phase region and water quenching in of the face-centered cubic γ-phase. In the Fe–Ni phase diagram there is a strong compositional dependence of the Curie temperature, Tc, on composition in the γ-phase. This work studies the stabilization of γ-phase nanostructures and the compositional tuning of Tc in Fe–Ni alloys which can have important ramifications on the self-regulated heating of magnetic nanoparticles in temperature ranges of interest for applications in polymer curing and cancer thermotherapies. To date we have achieved Curie temperatures as low as 120 °C by this method.
Nanocrystalline SmCo5 magnet synthesized by spark plasma sintering
Authors: Zhang D. T. , Lv W. C. , Yue M. , Yang J. J. , Liu W. Q. , Zhang J. X. , Qiang Y.
Published: April 2010

The structure and magnetic properties were studied for bulk nanocrystalline SmCo5 sintered magnet produced by spark plasma sintering technique. X-ray diffraction patterns show that the sintered magnet exhibits CaCu5 crystal structures. Transmission electron microscopy (TEM) observation indicates the average grain size of the magnet of about 40 nm. Magnetic measurement shows that the coercivity reaches as high as 2.85 T; the saturation magnetization and the remanence are 0.71 and 0.5 T, respectively. The magnet exhibits good thermal stability with a coercivity of 0.9 T at 773 K and a coercivity coefficient β of −0.15%/K.
Hot-deformed Sm–Co/Co composite magnets fabricated from powder blends
Authors: Gabay A. M. , Hadjipanayis G. C. , Marinescu M. , Liu J. F.
Published: April 2010

Composite magnets containing Sm–Co and Co phases were prepared from high-energy-milled Sm–Co and Sm–(Co,Fe,Mn) powders with the 1:5 and 2:7 stoichiometries blended with a micron-size Co powder. The blending was done via high-energy milling in argon or heptane; the blends were subsequently consolidated at 650 °C and subjected to a 65% plastic deformation at 800 °C. Both the premilling of Sm–Co component and the processing environment markedly influenced the microstructure and magnetic properties of the resulting composites. After blending in heptane, the composites made from the 1:5 and Co phases still contained these two phases in addition to the emerging 2:17 phase. Addition of oleic acid as a surfactant led not only to a more uniform and refined microstructure but also to a significant oxidation. After blending in argon, the composites made from the 1:5(2:7) and Co phases exhibited a two-phase structure with 80 nm Co inclusions embedded in a 2:17 matrix. Unfortunately, the newly formed 2:17 phase did not inherit the texture induced in the 1:5(2:7) precursors by the hot-deformation. Although the argon-blended composites were magnetically superior to the heptane-blended ones, they exceeded the maximum energy product of the single-alloy magnets with the same overall composition only when the Sm(Co,Fe,Mn)5 powder had been used as a precursor. The highest properties obtained were 8.8 kG, 6.3 kOe, and 13.1 MGOe for the remanence, coercivity, and energy product, respectively.
Enhancement of coercivity for melt-spun SmCo7−xTax ribbons with Ta addition
Authors: Guo Z. H. , Hsieh C. C. , Chang H. W. , Zhu M. G. , Pan W. , Li A. H. , Chang W. C. , Li W.
Published: April 2010

The effect of Ta addition on the structure and magnetic properties of melt-spun SmCo7−xTax (x=0–0.6) ribbons has been investigated. The intrinsic coercivity increases dramatically from 1.9 kOe for Ta-free ribbon to 9.8 kOe for SmCo6.7Ta0.3 ribbon, while further increasing Ta results in little enhancement of the coercivity. XRD patterns reveal that SmCo7−xTax ribbons crystallize in the pure TbCu7-type structure for low Ta substitution of x≤0.3 and a minor phase of TaCo3 appears when x>0.3. According to Rietveld structure refinement, the ternary alloying element Ta prefers to occupy the 2e site of TbCu7-type structure. The mechanism of the coercivity enhancement has been discussed based on crystal structure and microstructure.
Effects of substrate temperature and Cu underlayer thickness on the formation of SmCo5(0001) epitaxial thin films
Authors: Ohtake Mitsuru , Nukaga Yuri , Kirino Fumiyoshi , Futamoto Masaaki
Published: April 2010

SmCo 5 ( 0001 ) epitaxial thin films were prepared on Cu(111) underlayers heteroepitaxially grown on Al2O3(0001) single-crystal substrates by molecular beam epitaxy. The effects of substrate temperature and Cu underlayer thickness on the crystallographic properties of SmCo5(0001) epitaxial films were investigated. The Cu atoms of underlayer diffuse into the SmCo5 film and substitute the Co sites in SmCo5 structure forming an alloy compound of Sm(Co,Cu)5. The ordered phase formation is enhanced with increasing the substrate temperature and with increasing the Cu underlayer thickness. The Cu atom diffusion into the SmCo5 film is assisting the formation of Sm(Co,Cu)5 ordered phase.
The magnetization behavior and magnetic viscosity of Sm(Co,Fe,Cu,Zr)Z ribbons with different temperature dependence of coercivity
Authors: Wang Jinzhi , Chen Renjie , Rong Chuanbing , Liu Zhuang , Zhang Hongwei , Shen Baogen , Yan Aru
Published: April 2010

Two types of Sm(Co,Fe,Cu,Zr)Z ribbons with different temperature dependence of coercivity are investigated in comparison at different temperatures. It is found that their magnetization behaviors and magnetic viscosity are distinctly different. The magnetization of sample A (with abnormal temperature dependence of coercivity) behaves as a single phase permanent magnet at room temperature, and then becomes similar to a nanocomposite magnet with the increase of temperature. However, sample B (with negative temperature coefficient of coercivity) is similar to a nanocomposite magnet at the whole temperature range. The magnetic viscosity is mainly determined by the irreversible magnetization for both ribbons, while there emerges an extra small peak of magnetic viscosity coefficient S(H) at low field and high temperature for sample B. The different content and distribution of Cu in the cell boundary phase are proposed to be responsible for the differences of temperature dependence of coercivity, magnetization, and magnetic viscosity behaviors of these two types of Sm(Co,Fe,Cu,Zr)Z ribbons.
Preparation of SmNi5 and Sm(Ni,T)5 [T=Co,Fe] ordered alloy thin films on Cu(111) underlayers
Authors: Ohtake Mitsuru , Yabuhara Osamu , Nukaga Yuri , Kirino Fumiyoshi , Futamoto Masaaki
Published: April 2010

SmNi 5 and Sm(Ni,T)5 [T=Co,Fe] epitaxial thin films with the c-axis perpendicular to the substrate surface are successfully prepared on Cu underlayers heteroepitaxially grown on MgO(111) single-crystal substrates. The nucleation behavior of SmNi5 and Sm(Ni,T)5 crystals on Cu(111) underlayers were investigated. The SmNi5 and the Sm(Ni,Co)5 films consist of two types of domains whose orientations are rotated around the film normal by 30° each other, whereas the Sm(Ni,Fe)5 film is a single crystal. The nucleation and the domain volume ratio seem to be controllable by adjusting the kind and the composition of transition metal elements.
Magnetocaloric effect in Gd/W thin film heterostructures
Authors: Miller Casey W. , Williams D. V. , Bingham N. S. , Srikanth H.
Published: April 2010

In an effort to understand the impact of nanostructuring on the magnetocaloric effect, we have grown and studied gadolinium in MgO/W(50 Å)/[Gd(400 Å)/W(50 Å)]8 heterostructures. The entropy change associated with the second-order magnetic phase transition was determined from the isothermal magnetization for numerous temperatures and the appropriate Maxwell relation. The entropy change peaks at a temperature of 284 K with a value of approximately 3.4 J/kg K for a 0–30 kOe field change; the full width at half max of the entropy change peak is about 70 K, which is significantly wider than that of bulk Gd under similar conditions. The relative cooling power of this nanoscale system is about 240 J/kg, somewhat lower than that of bulk Gd (410 J/kg). An iterative Kovel–Fisher method was used to determine the critical exponents governing the phase transition to be β=0.51, and γ=1.75. Along with a suppressed Curie temperature relative to the bulk, the fact that the convergent value of γ is that predicted by the two-dimensional Ising model may suggest that finite size effects play an important role in this system. Together, these observations suggest that nanostructuring may be a promising route to tailoring the magnetocaloric response of materials.
The study on the microstructure and the magnetocaloric effects in LaFe10.8Co0.7Si1.5C0.2 compound at different annealing times
Authors: Bao Bo , Long Yi , Fu Bin , Wang Chaolun , Ye Rongchang , Chang Yongqin , Zhao Jinliang , Shen Jun
Published: April 2010

Microstructure and magnetocaloric effects in LaFe10.8Co0.7Si1.5C0.2 compound produced by induction furnace were investigated. NaZn13-type structure (1:13) formed in LaFe10.8Co0.7Si1.5C0.2 compound after being annealed at 1373 K for only 6 h. As annealing time increases, the grains grow up irregularly. A nearly single 1:13 phase is obtained after being annealed for 2 days. Annealing time is significantly reduced compared with that in conventional bulk LaFe13−xSix compounds. The short annealing time is of great advantage to application. The maximum magnetic entropy change of this compound is −4.9 J/K Kg under a magnetic field of 2 T and relative cooling power is 172.2 J/Kg.
Magnetic structure and magnetic entropy change in the intermetallic compound DyCoAl
Authors: Chelvane J. Arout , Das Tilak , Mahato Rabindra Nath , Morozkin A. V. , Lamsal Jagat , Yelon W. B. , Nirmala R. , Malik S. K.
Published: April 2010

Magnetic and magnetocaloric properties of polycrystalline DyCoAl compound have been studied in fields up to 9 T. This compound orders ferromagnetically at ∼37 K (TC). A maximum magnetic entropy change of ∼−18 J/kg/K is obtained for a field change of 9 T near TC which is reasonably large. Low temperature neutron powder diffraction data indicate collinear ferromagnetic structure where Dy magnetic moments lie in the ab plane. At 10 K, the magnetic moment at Dy site is only ∼4.8μB.
Characterization of Cu buffer layers for growth of L1-FeNi thin films
Authors: Mizuguchi M. , Sekiya S. , Takanashi K.
Published: April 2010

A Cu(001) layer was fabricated on a Au(001) layer to investigate the use of Cu as a buffer layer for growing L10-FeNi thin films. The epitaxial growth of a Cu buffer layer was observed using reflection high-energy electron diffraction. The flatness of the layer improved drastically with an increase in the substrate temperature although the layer was an alloy (AuCu3). An FeNi thin film was epitaxially grown on the AuCu3 buffer layer by alternate monatomic layer deposition and the formation of an L10-FeNi ordered alloy was expected. The AuCu3 buffer layer is thus a promising candidate material for the growth of L10-FeNi thin films.
Magnetic properties of the ferrimagnetic FeCr2−xMxS4 (M=In,Al)
Authors: Kim Chin Mo , Kim Sam Jin , Son Bae Soon , Kim Chul Sung
Published: April 2010

The polycrystalline samples of ferrimagnetic FeCr2−xMxS4 (M=In,Al; x=0.1,0.3) have been studied with x-ray diffraction, magnetization, and Mössbauer spectroscopy measurements. The crystal structure was found to be cubic spinel with Fd-3m space group. The lattice constants (a0) of the samples were linearly increased with Al and In concentration. Mössbauer spectra of FeCr2−xMxS4 (M=In,Al; x=0.1,0.3) were obtained at various temperatures ranging from 4.2 to 300 K. Magnetic hyperfine field and electric quadrupole interactions for FeCr2−xMxS4 (M=In,Al; x=0.1) at 4.2 K have been fitted, yielding the following results: for M=Al, Hhf=139 kOe, ΔEQ=2.54 mm/s, θ=30°, φ=0.0°, η=0.9, and R=2.7; and for M=In, Hhf=126 kOe, ΔEQ=2.64 mm/s, θ=30°, φ=0.0°, η=1.0, and R=3.1. The isomer shift (δ) value of the FeCr2−xMxS4 (x=0.1) samples for both M=Al and In at 300 K was 0.50 mm/s, relative to the Fe metal, which is consistent with the Fe2+ valence state. The Debye temperatures (ΘD) of the FeCr2−xAlxS4 (x=0.1,0.3) sample were determined to be 299±5 and 247±5 K, respectively, and those of the FeCr2−xInxS4 (x=0.1,0.3) samples were determined to be 257±5 and 239±5 K, respectively.
Investigation on electromagnetic and microwave absorbing properties of La0.7Sr0.3MnO3−δ/carbon nanotube composites
Authors: Tsay C. Y. , Yang R. B. , Hung D. S. , Hung Y. H. , Yao Y. D. , Lin C. K.
Published: April 2010

In this study, the influence of the addition of carbon nanotube (CNT) (0, 0.5, 1.0, and 2.0 wt %) on complex permittivity, complex permeability, and reflection loss for La0.7Sr0.3MnO3−δ (LSMO)/polymer composites was investigated. Microwave absorbing composites were prepared by molding and curing a mixture of LSMO powders, CNTs, and epoxy resin. The complex permittivity and complex permeability for LSMO/CNT composites were examined by a cavity perturbation technique. The experimental results showed that the complex permittivity increased with increasing CNT addition and the imaginary part of the permeability decreased with rising frequency. In the present study, a microwave absorbing composite filled with 80 wt % LSOM powders and 2 wt % CNTs exhibited the optimum performance, that is, the microwave absorbing peak was −22.85 dB at 9.5 GHz and the −10 dB absorbing bandwidth reached 3.3 GHz for the sample with a matching thickness of 3 mm.
Appearance of magnetization jumps in magnetic hysteresis curves in spinel oxide FeV2O4
Authors: Nishihara Sadafumi , Doi Wataru , Ishibashi Hiroki , Hosokoshi Yuko , Ren Xiao-Ming , Mori Shigeo
Published: April 2010

We report the appearance of magnetization jumps in the magnetic hysteresis curves of the spinel oxide FeV2O4, in which two different magnetic transition ions appeared, both of them having orbital degrees of freedom. The spin-glass-like transition was observed from ac magnetic susceptibilities and the transition temperature was estimated to be Tg=85.5 K. The magnetization jumps appear below 90 K at B=0. In addition, jumps at B=±1.2 T appear below 4.6 K. The magnetization jumps at B=0 may be correlated with spin-glass-like behaviors.
dc magnetoelectric sensor based on direct coupling of Lorentz force effect in aluminum strip with transverse piezoelectric effect in 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 single-crystal plate
Authors: Leung Chung Ming , Or Siu Wing , Ho Siu Lau
Published: April 2010

We report theoretically and experimentally a dc magnetoelectric sensor consisting of a thickness-polarized 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 (PMN-PT) piezoelectric single-crystal plate arranged along the longitudinal direction and sandwiched between a pair of electrically connected aluminum strips. The operation of the sensor is based on the direct coupling of the Lorentz force effect in the aluminum strips in response to an applied dc magnetic field under a reference ac electric current with the transverse piezoelectric effect in the PMN-PT single-crystal plate. The sensor shows a good linear ac electric voltage response to broad ranges of applied dc magnetic field of 0–180 mT and reference ac electric current of 1–100 mA, giving a high and linear current-controlled dc magnetic field sensitivity of 0.23 V/T/A. It also provides the direction information of the applied dc magnetic field.
Broadband femtosecond circular dichroism spectrometer with white-light polarization control
Authors: Trifonov Anton , Buchvarov Ivan , Lohr Andreas , Würthner Frank , Fiebig Torsten
Published: April 2010

A broadband, femtosecond transient circular dichroism (TRCD) spectrometer has been developed and tested in the wavelength range from 350 to 700 nm. The spectrometer uses a femtosecond probe white light with well-defined circular polarization. The latter is modulated by the polarization of a narrowband seed pulse. We have implemented a dual-beam probe geometry with phase-locked detection technique to increase the signal-to-noise ratio and to reduce optical artifacts. The spectrometer allows the acquisition of TRCD spectra with subpicosecond time resolution and typical noise levels of 10−4 absorbance units. The performance of this instrument has been demonstrated on bis(merocyanine) nanorod aggregates in tetrahydrofurane/methylcyclohexane solution. The case study confirmed that this spectrometer is effective for the investigation of chiral properties in various molecular and nanostructural systems that have transient spectra in the UV-visible spectral range.
Optimization of multilayer porous silicon antireflection coatings for silicon solar cells
Authors: Selj J. H. , Thøgersen A. , Foss S. E. , Marstein E. S.
Published: April 2010

Efficient antireflection coatings (ARC) improve the light collection and thereby increase the current output of solar cells. In this work, multilayered refractive index stacks optimized for antireflection, in bare air and within modules, are modeled. The relation between porous silicon (PS) etching parameters and PS structure is carefully investigated using spectroscopic ellipsometry, gravimetry, x-ray photoelectron spectroscopy, and scanning electron microscopy. The close relation between porosity and refractive index, modeled using the Bruggeman effective medium approximation, allows PS multilayers to be tailored to fabricate the optimized ARCs. Limits imposed by efficient application in photovoltaics, such as thickness restrictions and the angular distribution of incident light, are examined and accounted for. Low reflectance multilayer ARCs are fabricated with integrated reflectances of ∼3% in air and 1.4% under glass in the wavelength range 400–1100 nm.
Magnetocaloric effect in GdGeSi compounds measured by the acoustic detection technique: Influence of composition and sample treatment
Authors: Guimarães A. O. , Soffner M. E. , Mansanares A. M. , Coelho A. A. , Carvalho A. Magnus G. , Pires M. J. M. , Gama S. , da Silva E. C.
Published: April 2010

In this paper we explore the acoustic detection method applied to the investigation of the magnetocaloric effect in Gd and Gd5(Ge1−xSix)4 compounds, in the temperature range from 230 to 360 K and for magnetic fields up to 20 kOe. Measurements were performed in as-cast materials, both for powder and pellet samples, and in tree samples with compositions around Gd5Ge2Si2 that underwent different thermal treatments. Small differences were observed when comparing powder and pellet samples of Gd and Gd5(Ge1−xSix)4 compounds with 0.500<x≤1.00. For the alloys with composition around Gd5Ge2Si2, which exhibit giant magnetostriction and coexistence of distinct phases, expressive changes were observed when comparing powder and pellet samples. Based on these cases, it is easy to see that the acoustic method can distinguish a second-order phase transition from a first-order magnetic-crystallographic one, and that it presents good sensitivity to detect spurious material phase in small quantities.
Cooperative hydrophobic/hydrophilic interactions in the hydration of dimethyl ether
Authors: Utiramerur S. , Paulaitis M. E.
Published: April 2010

Cooperative interactions in the hydration of dimethyl ether (DME) relative to its purely hydrophobic analog, propane, are analyzed by expressing the free energy of hydration in terms of an “inner-shell” contribution from water molecular packing and chemical association, and an “outer-shell” contribution described by the mean binding energy of the solute to the solution and fluctuations in this binding energy. We find that nonadditive, cooperative interactions associated with strong correlations in the binding energy fluctuations of the methyl groups and ether oxygen play a dominant role in the hydration of DME relative to propane. The electrostatic nature of these interactions is revealed in a multi-Gaussian analysis of hydration substates, which shows that the formation of favorable ether oxygen-water hydrogen bonds is correlated with less favorable methyl group-water interactions, and vice versa. We conclude that the group additive distinction between the hydrophobic hydration of the DME methyl groups and hydrophilic hydration of the ether oxygen is lost in the context of these cooperative interactions. Our results also suggest that the binding energy fluctuations of constituent hydrophobic/hydrophilic groups are more sensitive than local water density fluctuations for characterizing the hydration of heterogeneous interfaces.
The defect character of GaN growth on r-plane sapphire
Authors: Smalc-Koziorowska J. , Tsiakatouras G. , Lotsari A. , Georgakilas A. , Dimitrakopulos G. P.
Published: April 2010

We study the influence of the heteroepitaxial interface on the defect content of nonpolar a-plane GaN grown on r-plane sapphire, using transmission electron microscopy techniques and the topological theory of interfacial defects. The structural mismatch is accommodated in different ways along distinct in-plane directions. For the misfit along the [0001] direction of GaN, the I1 basal stacking faults constitute the principal relaxation mechanism, through their delimiting partial dislocations. The misfit along [11¯00] is relaxed by misfit dislocations that have out-of-plane Burgers vectors causing rotational misorientations of the epilayer about [0001]. These misorientations lead to the introduction of low-angle tilt grain boundaries which are defect sources through their associated primary lattice dislocations. Furthermore, semipolar nanocrystals can nucleate on sapphire p-plane nanofacets, causing the introduction of threading dislocations (TDs) and stacking faults, when these nanocrystals are overgrown by the nonpolar epilayer. The semipolar nanocrystals bear a high-symmetry 90° [1¯21¯0] orientation relative to the nonpolar epilayer. The interfacial dislocations at the nonpolar/semipolar boundaries have suitable Burgers vectors to become TDs. These grain boundaries also promote the introduction of stacking faults and pockets of cubic GaN. The coexistence of semipolar orientation variants leads to twin boundaries and associated dislocations.
Atomization patterns produced by the oblique collision of two Newtonian liquid jets
Authors: Jung Sungjune , Hoath Stephen D. , Martin Graham D. , Hutchings Ian M.
Published: April 2010

This paper reports a detailed experimental investigation of the formation, destabilization, and atomization of the liquid sheets created by the oblique impact of two laminar jets of a Newtonian liquid. Glycerol-water mixtures with viscosities between 4 and 30 mPa s were used to investigate the effects of viscosity and jet velocity. The jets were ejected from parallel cylindrical nozzles with an internal diameter of 0.85 mm. Collision of the jets resulted in various regimes of behavior which depend on the jet velocities and the liquid properties. We focus on the regime where the impinging jets form a liquid sheet which then breaks up into a regular succession of ligaments and droplets, a so-called “fishbone” pattern. We use short-duration, single-flash illumination combined with high-resolution digital photography to study the evolution of the sheet, its shape, and the form, size, and spacing of resulting ligaments and drops. Unexpectedly, we found fishbone regimes corresponding to lower Reynolds and Weber numbers than had been previously reported; furthermore our apparently symmetric fishbone structures were definitely associated with asymmetric, rather than symmetric, impacting jet conditions. The fishbone structure was found to be significantly affected by any asymmetry in either the free lengths of the two jets or their alignment. The fishbone angle, defined as the angle between the lines through the first pairs of droplets on each side of the fishbone structure, is introduced to describe the effects of differences in jet length, alignment, or fluid properties on the degree of development of the fishbone pattern. We discuss how changes in the various parameters influence the form of the fishbone pattern and the origin and mechanism of the periodic atomization of the sheet. In particular we find that the dependence of the drop spacing on viscosities is consistent with the Rayleigh–Plateau instability on the rim provided the variation of the rim width is properly included, as this dominates the Ohnesorge number dependence of the breakup.
Perpendicular magnetic anisotropy in Co/Pt multilayers studied from a view point of anisotropy of magnetic Compton profiles
Authors: Ota M. , Itou M. , Sakurai Y. , Koizumi A. , Sakurai H.
Published: April 2010

Magnetic Compton profiles (MCPs) of Co/Pt multilayers have been measured from a view point of perpendicular magnetic anisotropy (PMA). The PMA and the MCPs are discussed in the present Co/Pt results together with the previous Co/Pd results. The anisotropies of the MCPs have been decomposed into each magnetic quantum number |m|=0, 1, and 2. The decomposition analysis has suggested that the |m|=1 state contributes to the PMA when the multilayer films change in-plane magnetic anisotropy to the PMA, and that the |m|=2 state contributes to the PMA when the multilayer films have large PMA energy.
Asymmetric criticality in weakly compressible liquid mixtures
Authors: Pérez-Sánchez G. , Losada-Pérez P. , Cerdeiriña C. A. , Sengers J. V. , Anisimov M. A.
Published: April 2010

The thermodynamics of asymmetric liquid-liquid criticality is updated by incorporating pressure effects into the complete-scaling formulation earlier developed for incompressible liquid mixtures [C. A. Cerdeiriña et al., Chem. Phys. Lett. 424, 414 (2006); J. T. Wang et al., Phys. Rev. E 77, 031127 (2008)]. Specifically, we show that pressure mixing enters into weakly compressible liquid mixtures as a consequence of the pressure dependence of the critical parameters. The theory is used to analyze experimental coexistence-curve data in the mole fraction–temperature, density-temperature, and partial density–temperature planes for a large number of binary liquid mixtures. It is shown how the asymmetry coefficients in the scaling fields are related to the difference in molecular volumes of the two liquid components. The work resolves the question of the so-called “best order parameter” discussed in the literature during the past decades.
The structure of the NO(X Π2)−N2 complex: A joint experimental-theoretical study
Authors: Wen B. , Meyer H. , Kłos J.
Published: April 2010

We report the first measurement of the spectrum of the NO–N2 complex in the region of the first vibrational NO overtone transition. The origin band of the complex is blueshifted by 0.30 cm−1 from the corresponding NO monomer frequency. The observed spectrum consists of three bands assigned to the origin band, the excitation of one quantum of z-axis rotation and one associated hot band. The spacing of the bands and the rotational structure indicate a T-shaped vibrationally averaged structure with the NO molecule forming the top of the T. These findings are confirmed by high level ab initio calculations of the potential energy surfaces in planar symmetry. The deepest minimum is found for a T-shaped geometry on the A″-surface. As a result the sum potential also has the global minimum for this structure. The different potential surfaces show several additional local minima at slightly higher energies indicating that the complex most likely will perform large amplitude motion even in its ground vibrational state. Nevertheless, as suggested by the measured spectra, the complex must, on average, spend a substantial amount of time near the T-shaped configuration.
Correlation of the scaling exponent γ of the diffusivity-density function in viscous liquids with their elastic properties
Authors: Papathanassiou Anthony N. , Sakellis Ilias
Published: April 2010

Fundamental thermodynamical concepts and a solid-state point defect elastic model are used to formulate a diffusivity-density scaling function for viscous liquids. It is proved in a straightforward manner that the scaling exponent γ describing the density scaling of the diffusivity is related with the pressure derivative of the isothermal bulk modulus.
Active-space completely-renormalized equation-of-motion coupled-cluster formalism: Excited-state studies of green fluorescent protein, free-base porphyrin, and oligoporphyrin dimer
Authors: Kowalski Karol , Krishnamoorthy Sriram , Villa Oreste , Hammond Jeff R. , Govind Niranjan
Published: April 2010

The completely renormalized equation-of-motion coupled-cluster approach with singles, doubles, and noniterative triples [CR-EOMCCSD(T)] has proven to be a reliable tool in describing vertical excitation energies in small and medium size molecules. In order to reduce the high numerical cost of the genuine CR-EOMCCSD(T) method and make noniterative CR-EOMCCSD(T) approaches applicable to large molecular systems, two active-space variants of this formalism [the CR-EOMCCSd(t)-II and CR-EOMCCSd(t)-III methods], based on two different choices of the subspace of triply excited configurations employed to construct noniterative correction, are introduced. In calculations for green fluorescent protein (GFP) and free-base porphyrin, where the CR-EOMCCSD(T) results are available, we show good agreement between the active-space CR-EOMCCSD(T) (variant II) and full CR-EOMCCSD(T) excitation energies. For the oligoporphyrin dimer (P2TA) active-space CR-EOMCCSD(T) results provide reasonable agreement with experimentally inferred data. For all systems considered we demonstrated that the active-space CR-EOMCCSD(T) corrections lower the EOMCCSD (iterative equation-of-motion coupled-cluster method with singles and doubles) excitation energies by 0.2 and 0.3 eV, which leads to a better agreement with experiment. We also discuss the quality of basis sets used and compare EOMCC excitation energies with excitation energies obtained with other methods. In particular, we demonstrate that for GFP and FBP Sadlej’s TZP and cc-pVTZ basis sets lead to a similar quality of the EOMCC results. The performance of the CR-EOMCCSD(T) implementation is discussed from the point of view of timings of iterative parts and scalability of the most expensive, N7, part of the calculation. In the latter case the scalability across 34 008 processors is reported.
Fluctuations in gene regulatory networks as Gaussian colored noise
Authors: Huang Ming-Chang , Wu Jinn-Wen , Luo Yu-Pin , Petrosyan Karen G.
Published: April 2010

The study of fluctuations in gene regulatory networks is extended to the case of Gaussian colored noise. First, the solution of the corresponding Langevin equation with colored noise is expressed in terms of an Ito integral. Then, two important lemmas concerning the variance of an Ito integral and the covariance of two Ito integrals are shown. Based on the lemmas, we give the general formulas for the variances and covariance of molecular concentrations for a regulatory network near a stable equilibrium explicitly. Two examples, the gene autoregulatory network and the toggle switch, are presented in details. In general, it is found that the finite correlation time of noise reduces the fluctuations and enhances the correlation between the fluctuations of the molecular components.
Semiconductor saturable absorbers for ultrafast terahertz signals
Authors: Hoffmann Matthias C. , Turchinovich Dmitry
Published: April 2010

We demonstrate saturable absorber behavior of n-type semiconductors GaAs, GaP, and Ge in the terahertz (THz) frequency range at room temperature using nonlinear THz spectroscopy. The saturation mechanism is based on a decrease in electron conductivity of semiconductors at high electron momentum states, due to conduction band nonparabolicity and scattering into satellite valleys in strong THz fields. Saturable absorber parameters, such as linear and nonsaturable transmission, and saturation fluence, are extracted by fits to a classic saturable absorber model. Further, we observe THz pulse shortening, and an increase in the group refractive index of the samples at higher THz pulse peak fields.
Numerical modeling of a table-top tunable Smith–Purcell terahertz free-electron laser operating in the super-radiant regime
Authors: Prokop C. , Piot P. , Lin M. C. , Stoltz P.
Published: April 2010

Terahertz (THz) radiation occupies a very large portion of the electromagnetic spectrum and has generated much recent interest due to its ability to penetrate deep into many organic materials without the damage associated with ionizing radiation such as x-rays. One path for generating copious amount of tunable narrow-band THz radiation is based on the Smith–Purcell free-electron laser (SPFEL) effect. In this paper we propose a simple concept for a compact two-stage tunable SPFEL operating in the super-radiant regime capable of radiating at the fundamental bunching frequency. We demonstrate its capabilities and performances using the conformal finite-difference time-domain electromagnetic solver VORPAL.
High work function transparent middle electrode for organic tandem solar cells
Authors: Moet D. J. D. , de Bruyn P. , Blom P. W. M.
Published: April 2010

The use of poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) in combination with ZnO as middle electrode in solution-processed organic tandem solar cells requires a pH modification of the PEDOT:PSS dispersion. We demonstrate that this neutralization leads to a reduced work function of PEDOT:PSS, which does not affect the performance of polythiophene:fullerene solar cells, but results in a lower open-circuit voltage of devices based on a polyfluorene derivative with a higher ionization potential. The introduction of a thin layer of a perfluorinated ionomer recovers the anode work function and gives an open-circuit voltage of 1.92 V for a double junction polyfluorene-based solar cell.
Communications: Explicitly correlated second-order Møller–Plesset perturbation method for extended systems
Authors: Shiozaki Toru , Hirata So
Published: April 2010

A formalism for the second-order Møller–Plesset perturbation method employing basis functions that depend explicitly on electron-electron distances (the MP2-R12 or F12 method) is derived and implemented into computer codes for extended systems periodic in one dimension. The excitation amplitudes on these functions are held fixed at values that satisfy the first-order cusp condition. Necessary many-electron integrals over Gaussian-type functions involving Slater-type geminals are evaluated by means of the resolution-of-the-identity approximation with a complementary auxiliary basis set. These integrals and thus the final correlation energy are shown to have the correct size dependence. The valence MP2 correlation energy of polyethylene near the complete basis-set limit is obtained and shown to be considerably greater in magnitude than the value obtained without the R12 treatment.
Resonant photoluminescent charging of epitaxial graphene
Authors: Lounis S. D. , Siegel D. A. , Broesler R. , Hwang C. G. , Haller E. E. , Lanzara A.
Published: April 2010

Photoluminescence spectroscopy (PL) and angle resolved photoemission spectroscopy have been used to study the interaction between epitaxially grown graphene and the silicon carbide (SiC) substrate. We report evidence of an anomalous temperature dependent shift in the Fermi energy with a maximum at 65 K. A similarly anomalous onset of the photoluminescence spectrum is also observed at this temperature. These results are explained by the formation of a Schottky barrier at the graphene/SiC interface, which is also responsible for large electron doping of epitaxially grown graphene films. Moreover, we identify a strong resonance between the sharp no-phonon peaks of the D1 photoluminescence spectrum in SiC and the electronic transition across the barrier, suggesting that epitaxial graphene might be also used to selectively detect photons of precise energies.
In situ x-ray diffraction study of graphitic carbon formed during heating and cooling of amorphous-C/Ni bilayers
Authors: Saenger K. L. , Tsang J. C. , Bol A. A. , Chu J. O. , Grill A. , Lavoie C.
Published: April 2010

We examine graphitization of amorphous carbon (a-C) in a-C/Ni bilayer samples having the structure Si/SiO2/a-C(3–30 nm)/Ni(100 nm). In situ x-ray diffraction (XRD) measurements during heating in He at 3 °C/s to 1000 °C showed graphitic C formation beginning at temperatures T of 640–730 °C, suggesting graphitization by direct metal-induced crystallization, rather than by a dissolution/precipitation mechanism in which C is dissolved during heating and expelled from solution upon cooling. We also find that graphitic C, once formed, can be reversibly dissolved by heating to T>950 °C, and that nongraphitic C can be volatilized by annealing in H2-containing ambients.
Ultimate quality factor of silica microtoroid resonant cavities
Authors: Zhang Xiaomin , Choi Hong Seok , Armani Andrea M.
Published: April 2010

Silica optical microcavities with quality (Q factors above 1×108 have applications throughout science and engineering. While both the microtoroid and microsphere resonant cavity have demonstrated Q>1×108, only the microsphere has surpassed 1×109. Surprisingly, the reason for this performance disparity is directly related to type of silicon substrate used in the fabrication process. In the present work, the theoretical Q of planar toroidal silica resonant cavities is calculated and compared to experimental results from a series of devices fabricated from oxide on doped silicon wafers. As predicted, the Q depends on the substrate dopant concentration.
Polydimethylsiloxane-enclosed liquid crystal lasers for lab-on-chip applications
Authors: Schmidtke Jürgen , Terentjev Eugene M.
Published: April 2010

We demonstrate the operation of a self-organized cholesteric liquid crystal laser confined between optically clear and elastic polydimethylsiloxane (PDMS) substrates. The formation of a planar helical texture in the cholesteric was supported by microsctructuring of PDMS layer surface, using the nanoembossing technique with glass substrates coated with conventional alignment layers as a template. The potential of combining miniature cholesteric laser sources and microfluidic devices for lab-on-chip applications is discussed.
Ultraviolet GaN-based microdisk laser with AlN/AlGaN distributed Bragg reflector
Authors: Chen Cheng-Chang , Shih M. H. , Yang Yi-Chun , Kuo Hao-Chung
Published: April 2010

We demonstrated a 4.7 μm GaN-based microdisk laser with 25-pair AlN/AlGaN distributed Bragg reflector in ultraviolet range without undercut or deeply-etching procedures. The distributed Bragg reflector provides a high reflectivity of 85%, and selects lasing mode around 375 nm wavelength. Under optical pumping conditions, the lasing action was observed with a low threshold power density of 0.03 kW/cm2. We also characterized the whispering gallery mode profiles of the microdisk with finite-different time-domain simulation.
Microwave resonances of a hairpin probe in a magnetized plasma
Authors: Gogna G. S. , Karkari S. K.
Published: April 2010

The effect due to the electron cyclotron frequency on the microwave resonances of a hairpin probe is investigated in a moderate to strongly magnetized plasma. The magnetic field is independently varied over a wide range from 0.01–0.13 T while maintaining the local plasma density constant. At strong magnetic fields the resonance frequency is found to be lower than that measured in vacuum implying that the relative plasma dielectric permittivity, εp>1. It is proposed that the experiments reported here are consistent with a permittivity model that includes magnetic field.
Confinement in PbSe wires grown by rf magnetron sputtering
Authors: Jung Hyeson , Kuljic Rade , Stroscio Michael A. , Dutta Mitra
Published: April 2010

Lead selenide (PbSe) nanowires were grown by magnetron sputtering on silicon with silicon dioxide (SiO2/Si) substrates, and characterized by scanning electron microscopy, x-ray diffraction, Fourier transform infrared spectroscopy, photoluminescence, and x-ray photoelectron spectroscopy. Closely packed PbSe nanowires of approximately 100 nm diameter grew in the ⟨111⟩ rock-salt cubic structure orientation. These large wires showed a large blueshift in the luminescence and absorption compared to the bulk crystal, demonstrating quantum confinement. This is attributed to a strong built-in field due to surface states, band bending, and a depletion layer which confines the carrier states.
Effects of metal buffer layer on characteristics of surface acoustic waves in ZnO/metal/diamond structures
Authors: Chiang Yuan-Feng , Sung Chia-Chi , Ro Ruyen
Published: April 2010

The interdigital transducer (IDT)/ZnO/metal/diamond structure is investigated for use in the design surface acoustic wave (SAW) devices in the super-high-frequency (SHF) band. Simulation results indicate that adding a metal buffer layer with a finite thickness significantly increases the coupling coefficient. In the Sezawa mode, the coupling coefficient is 4.71% when an Al interlayer is applied. This coupling coefficient is 75% and 77% larger than those in the IDT/ZnO/diamond and IDT/ZnO/shorted surface/diamond structures, respectively. The results in this study are useful in designing SAW devices using diamond-based structures with a large coupling coefficient in the SHF band.
Multifrequency continuous wave terahertz spectroscopy for absolute thickness determination
Authors: Scheller Maik , Baaske Kai , Koch Martin
Published: April 2010

We present a tunable multifrequency continuous wave terahertz spectrometer based on two laser diodes, photoconductive antennas, and a coherent detection scheme. The system is employed to determine the absolute thickness of samples utilizing a proposed synthetic difference frequency method to circumvent the 2π uncertainty known from conventional photomixing systems while preserving a high spatial resolution.
Determination of the sign of g factors for conduction electrons using time-resolved Kerr rotation
Authors: Yang C. L. , Dai Junfeng , Ge W. K. , Cui Xiaodong
Published: April 2010

The knowledge of electron g factor is essential for spin manipulation in the field of spintronics and quantum computing. While there exist technical difficulties in determining the sign of g factor in semiconductors by the established magneto-optical spectroscopic methods. We develop a technique to precisely measure the sign and the amplitude of electron g factor in semiconductors using time resolved Kerr rotation.
Light detection enhanced by surface plasmon resonance in metal film
Authors: Fukuda Mitsuo , Aihara Takuma , Yamaguchi Kenzo , Ling Yu Y. , Miyaji Kazuma , Tohyama Makoto
Published: April 2010

Light detection enhanced by surface plasmons was confirmed in Au film/n-type Si Schottky structures. Electrons excited directly with light in Au film overflowed into the n-type silicon, and this excitation was enhanced by surface plasmons induced by Au nanorods attached to the Au film. Excitation was clearly observed in a wavelength range corresponding to the energy of less than the band gap of silicon. The feasibility of Schottky-type photodiodes, in which electrons were never generated by absorption in semiconductors but directly excited in metal, was experimentally demonstrated.
The effects of early and late-season fires on mortality, dispersal, physiology and breeding of red-backed fairy-wrens (Malurus melanocephalus)
Authors: Murphy Stephen A. , Legge Sarah M. , Heathcote Joanne , Mulder Eridani
Published: April 2010

Context. Mismanaged fire is one of the main processes threatening biodiversity in northern Australian savannas. While the suite of species adversely affected by fire has been quite well documented, empirical studies that seek to identify the ecological mechanisms that underpin these declines are rare. This dearth of mechanistic knowledge is hindering the refinement and development of conservation management practices and policy, such as early dry-season prescribed burning programmes. Aims. Our aim was to describe why red-backed fairy-wrens (RBWs; Malurus melanocephalus) decline after fire, as shown by previous studies. Methods. We examined the effects of early and late dry-season fire (and an unburnt control) on the mortality, dispersal, physiology and breeding of colour-marked RBWs. We also tested whether the early fire area became an important refuge after the late fire. Key results. Neither fire treatment caused a detectable increase in mortality. Individuals relocated short distances to unburnt habitat following both fires. Some individuals used the early fire area after the late fire, but only if they were already living nearby and most also relied on adjacent unburnt habitat. Blood-parasite infection and pectoral-muscle attrition were unaffected by the treatments. The early fire caused loss of body mass at a time when the control population gained mass after breeding, whereas the late fire had no effect on mass. Blood haemoglobin concentrations in birds affected by the late fire deviated from the levels observed in the control population, presumably because of disruption of behaviours associated with the onset of the breeding season. Mayfield estimations of daily egg-survival probability showed no difference among the treatments, whereas the daily probability of nestling survival was significantly lower in the late fire area. Pairs affected by the late fire also had a shorter breeding season and none attempted multiple broods after earlier successes. Conclusions. Our results suggest that the reproductive output of RBWs is low following late dry-season fire, and that this is the main mechanism that explains their decline. Implications. This study provides support for the value of using early dry-season prescribed burning to limit the effects of late dry-season wildfire. However, there are important caveats to this, such as the retention of near-by unburnt habitat, and the consideration of variable regeneration rates for different vegetation types.