bluuebunny/crossref_metadata_2025 huggingface dataset:
Persistence of bending and torsional modes in piezoelectric-excited millimeter-sized cantilever (PEMC) sensors in viscous liquids - 1 to 103 cP
Authors: Johnson Blake N. , Mutharasan Raj
Published: March 2011

Cantilever sensors consisting of only a piezoelectric layer express both bending and torsional modes near ∼25 kHz that persist with reasonable Q-values (∼15) in liquids of high viscosity (>100 cP). Responses of both bending and torsional modes in liquids (1−1019 cP) were measured simultaneously. The bending mode response was more sensitive to mass-change effects than the torsional mode, and the response in liquids <70 cP matched theoretical values within 0.9%. At 1019 cP the bending mode response was within 10.4% of theory. The bending and torsional modes in PEMC can potentially be used simultaneously for bio-chemical sensing in very viscous samples.
Polaritons in an artificial ionic-type crystal made of two-dimensional periodically inversed multi-domain ferroelectric crystals
Authors: Yin Ruo-Cheng , He Cheng , Lu Ming-Hui , Lu Yan-Qing , Chen Yan-Feng
Published: March 2011

The polaritons in a two-dimensional artificial ionic-type crystal have been proposed and experimentally demonstrated from the two-dimensional periodically poled LiTaO3. In this artificially micro-structured materials, the anisotropic piezoelectric coefficients and the two-dimensional symmetric result in strong and complex couplings of the incident electromagnetic waves and the two-dimensional superlattice vibrations. We studied the dielectric anomalies, the coupling and transforming between two ordinary polariton modes etc., which reveal that, by engineering the ferroelectric domain’s distribution, the artificial ionic-type crystal may establish a new member of meta-materials, and will facilitate access to the device applications such as multi-directional and frequency transducers.
Proposal of the spin-polarization measurement using noncontact Andreev reflection
Authors: Ohtori Hiroyuki , Imamura Hiroshi
Published: March 2011

We theoretically analyzed the noncontact Andreev reflection in the normal-conductor/superconductor junction through the vacuum. We solved the Bogoliubov–de Gennes equations with the vacuum barrier by using the recursion-transfer-matrix method and showed that the noncontact Andreev reflection could be observed in the effective range of STM. The results showed that the noncontact Andreev reflection can be used as a tool for measuring the spin polarization of ferromagnetic materials.
Efficient spin injection into nonmagnetic metals through low-resistance MgO
Authors: Wang L. , Fukuma Y. , Idzuchi H. , Otani Y.
Published: March 2011

The effect of interface on the spin injection characteristics in lateral spin valves with Permalloy/MgO/Ag junctions has been studied. The spin valve signal drastically increases after the insertion of a thin MgO layer in the local and nonlocal spin injection schemes. We analyze our results based on the spin-dependent diffusion equation. This reveals that the interface resistance of ∼100 fΩm2 could effectively overcome the spin resistance mismatch between ferromagnetic and nonmagnetic metals.
Investigations on magnetic properties in ultrathin single crystal Fe rectangular arrays patterned by selective wet-etching
Authors: Sun L. , Wong P. K. J. , Niu D. X. , Zou X. , Zhai Y. , Wu J. , Xu Y. B. , Zhai H. R.
Published: March 2011

The magnetic properties of the rectangular element arrays of the ultrathin epitaxial Fe films on GaAs (100) have been studied with focused magneto-optical Kerr effect and ferromagnetic resonance. The coercivity increases upon decreasing aspect ratio of the elements. When the magnetic field is along the [0–11] direction of the GaAs substrate, which is the long edge of the element, a high remanent ratio of all the hysteresis loops is shown, indicating a global magnetic easy axis and a single domain remanent state, while along the [001] direction the breakage of the single domain remanent state occurs for the element with the aspect ratio lower than 2. These results are attributed to the competition among the intrinsic anisotropies, the demagnetizing field, and interelement dipole coupling as determined by the ferromagnetic resonance measurements.
Hard/graded exchange spring composite media based on FePt
Authors: Alexandrakis V. , Speliotis Th. , Manios E. , Niarchos D. , Fidler J. , Lee Jehyun , Varvaro G.
Published: March 2011

Hard-FePt(L10)/graded-FePt(L10 to A1) exchange spring composite media with perpendicular magnetic anisotropy have been studied. Changing the deposition temperature affects the structural transformation of FePt from cubic phase A1, which is magnetically soft, to the tetragonal phase L10, which is magnetically hard. Using this mechanism we were able to fabricate hard/graded composite films. Magnetic measurements revealed a significant reduction of the composite films’ switching fields in comparison with those of the single hard layer.
A path for conventional perpendicular recording to reach 1 Tb/in.2 and beyond
Authors: Wang Yiming , Park Soyoung , Zhu Jian-Gang
Published: March 2011

In this paper, we report micromagnetic analysis of a scheme for increasing area density capability in conventional perpendicular magnetic recording. By replacing a significant portion of the Ru intermediate layer in present film media with appropriate soft magnetic material, recording head field gradient can be effectively enhanced. A combined finite element method (FEM) and micromagnetic modeling study is conducted for the quantitative understanding of the area density gain along with recording geometry optimization. FEM calculation shows that by reducing air bearing surface to soft underlayer separation from 50 to 30 nm and the write gap from 35 to 20 nm, the on-track field gradient increases from 560 to 820 Oe/nm. The corresponding recording simulation on the same single layer medium shows almost 2 dB medium signal-to-noise ratio gain. The study also shows that the vertically segmented three-layer media used in current disk products can effectively further enhance the head field gradient, provided adequate vertical exchange coupling between the segments.
Low writing energy and sub nanosecond spin torque transfer switching of in-plane magnetic tunnel junction for spin torque transfer random access memory
Authors: Zhao H. , Lyle A. , Zhang Y. , Amiri P. K. , Rowlands G. , Zeng Z. , Katine J. , Jiang H. , Galatsis K. , Wang K. L. , Krivorotov I. N. , Wang J.-P.
Published: March 2011

This work investigated in-plane MgO-based magnetic tunnel junctions (MTJs) for the application of spin torque transfer random access memory (STT-RAM). The MTJ in this work had an resistance area product (RA) = 4.3 Ω·μm2, tunneling magnetoresistance ratio ∼135%, thermal stability factor Δ(H)=68 (by field measurement), and Δ(I) = 50 (by current measurement). The optimal writing energy was found to be 0.286 pJ per bit at 1.54 ns for antiparallel (AP) state to parallel (P) state switching, and 0.706 pJ per bit at 0.68 ns for P state to AP state switching. Ultra fast spin torque transfer (STT) switching was also observed in this sample at 580 ps (AP to P) and 560 ps (P to AP). As a result, 0.6–1.3 GHz was determined to be the optimal writing rate from writing energy consumption of view. These results show that in-plane MgO MTJs are still a viable candidate as the fast memory cell for STT-RAM.
Magnetic cluster expansion model for high-temperature magnetic properties of iron and iron–chromium alloys
Authors: Lavrentiev M. Yu. , Dudarev S. L. , Nguyen-Manh D.
Published: March 2011

Magnetic cluster expansion model is developed for bcc Fe–Cr alloys, and applied to the investigation of magnetic properties of these alloys over a broad interval of concentrations ranging from pure Fe to pure Cr, and over a broad interval of temperatures extending well over 1000 K. Finite-temperature configurations simulated using the magnetic cluster expansion Hamiltonian describe various magnetically ordered ferromagnetic and antiferromagnetic phases, partially magnetically ordered phases, and transitions between them and paramagnetic phases. We investigate the dependence of the Curie and Néel transition temperatures on the composition of the alloy. Analysis of the magnetic specific heat treated as a function of Cr concentration shows that in the low Cr concentration limit the Curie temperature increases as a function of Cr content. We find that for alloys containing high level of Cr the Curie temperature depends sensitively on the degree of Cr precipitation, varying by as much as 150 K between random alloy configurations and configurations containing Cr precipitates.
High field neutron diffraction study in Ce(Fe0.95Si0.05)2 compound
Authors: Haldar A. , Das A. , Hoser A. , Hofmann T. , Nayak A. K. , Suresh K. G. , Nigam A. K.
Published: March 2011

Si substitution at Fe site causes the ferromagnetic to antiferromagnetic (AFM) transition at low temperatures in CeFe2. We have carried out temperature and field variation of neutron diffraction measurements on Ce(Fe0.95Si0.05)2 to unravel its magnetic structure along with its lattice structure. The Curie temperature (TC) and the Neel temperature (TN) are 184 and 82 K, respectively. Above TN, it exhibits a cubic (Fd3¯m) structure. On lowering the temperature below TN, weak superlattice reflections are observed indicating the onset of AFM ordering accompanied by a rhombohedral distortion. The crystal structure in the AFM state is refined in R3¯m space group.
Spin-polarized metastable He study of surface magnetic order in Ho thin films
Authors: Pratt A. , Kurahashi M. , Yamauchi Y.
Published: March 2011

A spin-polarized metastable helium beam operating in magnetic fields of up to 5 T has been used to investigate the spin polarization at the surface of thin films of Ho(0001) grown on W(110) substrates. The extreme surface sensitivity of this technique allows a direct probe of the various magnetic structures that form as a function of film thickness, temperature, and applied magnetic field. Evidence for a transition from a conical ferromagnetic structure to a helical antiferromagnetic (AFM) phase is observed at low temperatures with a further transition to paramagnetism at close to the AFM ordering temperature, TN. In addition, the spin polarization of the 6s CE that mediate the exchange interaction between localized Ho 4f moments (the RKKY interaction) is found to be positive, supporting earlier observations.
Current induced vortices in multi-nanocontact spin-torque devices
Authors: Sani S. R. , Persson J. , Mohseni S. M. , Fallahi V. , Åkerman J.
Published: March 2011

We demonstrate spin transfer torque (STT) switching in multi-nanocontact STT devices fabricated using hole mask colloidal lithography. We also study the STT device resistance and switching properties as a function of applied magnetic field and nanocontact current. At low nanocontact current, magnetoresistance measurements show sharp, single-step switching at low switching fields. When the current is increased, the switching becomes multistep, and the switching field increases dramatically. We explain these results as arising from a transition from a predominantly single domain like switching to switching involving a vortex state. Micromagnetic simulations corroborate this picture, indicating that a single magnetic vortex nucleates in between the nanocontacts through the influence from the total Oersted field generated by the nanocontact ensemble.
Investigation of a magnetohyperthermia system efficacy
Authors: Portilho F. A. , Estevanato L. L. C. , Miranda-Vilela A. L. , Almeida-Santos M. F. M. , de Oliveira-Cavalcanti C. E. , Lacava B. M. , Simioni A. R. , Tedesco A. C. , Morais P. C. , Lacava Z. G. M.
Published: March 2011

This study reports on the successful use of magnetic albumin nanosphere (MAN) with in vivo magnetohyperthermia (MHT) in a mouse Ehrlich tumor. Maghemite nanoparticles (8.9 nm average diameter) were encapsulated within MAN (73.0 nm average diameter). Ehrlich tumor obtained after implantation of tumor cells in the subcutaneous tissue of mice was used as a model throughout this study. MHT was performed with MAN (40 μL) containing 1.2 × 1015 particle/mL and 40 Oe amplitude ac magnetic field oscillating at 1 MHz. Animals not treated, treated with MAN, or exposed to the ac field were used as controls. Histopathological analysis was carried out after 2, 5, or 11 days of tumor implantation. We found that the MHT most efficient condition was obtained while applying the ac field protocol twice a day during three consecutive days. Further, in this ac field-treated group no proliferation cells were detected.
Boron-Silicon complex defects in GaAs: An ab initio study
Authors: Leitsmann R. , Chicker F. , Plänitz Ph. , Radehaus C. , Kretzer U. , Scheffer-Czygan M. , Eichler S.
Published: March 2011

First principles calculations have been performed to investigate defect equilibria of the silicon–boron pair complex (Si–B) in a GaAs matrix. For several charge states, the formation energies were evaluated within the Car–Parrinello scheme considering cation and anion substitutional site defects. The calculations, including the full relaxation of all ionic coordinates, investigate native defects and isolated substitutional silicon (Si) and boron (B) impurities. The obtained formation energies are used to calculate the impurity concentration for different growth conditions. These results can be used to estimate the effect of different thermal profiles on the distribution and electrical state of Si and B defects, which is interesting for classical process simulations.
Magnetic and transport properties of Fe-Pd/Rh(Ir)/Fe-Pd multilayers
Authors: Vlaic P. , Burzo E.
Published: March 2011

The magnetic and transport properties of Fe-Pd/Rh(Ir)/Fe-Pd heterostructures have been analyzed by means of a first principles Green’s technique for surfaces and interfaces, implemented within tight-binding linear muffin-tin method. The effects of variable thicknesses both for spacers and magnetic layers on the magnetic and transport properties were analyzed. The spin-dependent transport properties are determined in the ballistic limit by means of linear response of Kubo approach implemented within tight-binding linear muffin-tin orbital formalism. A correlation between the interlayer exchange coupling, conductances, giant magnetoresistances and magnetic properties are shown. The magnetic disorder, simulating the effect of temperature on the interlayer exchange coupling and transport properties, are also discussed.
Dynamic properties of combustion instability in a lean premixed gas-turbine combustor
Authors: Gotoda Hiroshi , Nikimoto Hiroyuki , Miyano Takaya , Tachibana Shigeru
Published: March 2011

We experimentally investigate the dynamic behavior of the combustion instability in a lean premixed gas-turbine combustor from the viewpoint of nonlinear dynamics. A nonlinear time series analysis in combination with a surrogate data method clearly reveals that as the equivalence ratio increases, the dynamic behavior of the combustion instability undergoes a significant transition from stochastic fluctuation to periodic oscillation through low-dimensional chaotic oscillation. We also show that a nonlinear forecasting method is useful for predicting the short-term dynamic behavior of the combustion instability in a lean premixed gas-turbine combustor, which has not been addressed in the fields of combustion science and physics.
Spectral properties of chimera states
Authors: Wolfrum M. , Omel’chenko O. E. , Yanchuk S. , Maistrenko Y. L.
Published: March 2011

Chimera states are particular trajectories in systems of phase oscillators with nonlocal coupling that display a spatiotemporal pattern of coherent and incoherent motion. We present here a detailed analysis of the spectral properties for such trajectories. First, we study numerically their Lyapunov spectrum and its behavior for an increasing number of oscillators. The spectra demonstrate the hyperchaotic nature of the chimera states and show a correspondence of the Lyapunov dimension with the number of incoherent oscillators. Then, we pass to the thermodynamic limit equation and present an analytic approach to the spectrum of a corresponding linearized evolution operator. We show that, in this setting, the chimera state is neutrally stable and that the continuous spectrum coincides with the limit of the hyperchaotic Lyapunov spectrum obtained for the finite size systems.
Resonance tuning behavior in closely spaced inhomogeneous bilayer metamaterials
Authors: Reiten M. T. , Roy Chowdhury D. , Zhou J. , Taylor A. J. , O’Hara J. F. , Azad A. K.
Published: March 2011

We have measured the interaction between closely spaced bilayer split ring resonators (SRRs) by varying separation layer and orientation. Terahertz time domain measurements match closely to simulations for arrays separated by a thin micron-scale polyimide layer. Experimental results indicate that bilayer SRRs resonances strongly depend on interlayer coupling tunable by separation and orientation. Simulation shows a relatively high Q resonance (Q≈30) is associated with the “antialigned” SRR pair at separations of λ/500. Metamaterials tuned through interlayer coupling allows resonances at frequencies lower than the natural resonance of individual SRRs which has implications for electrically small antenna design.
The dynamics of the impact and coalescence of droplets on a solid surface
Authors: Castrejón-Pita J. R. , Betton E. S. , Kubiak K. J. , Wilson M. C. T. , Hutchings I. M.
Published: March 2011

A simple experimental setup to study the impact and coalescence of deposited droplets is described. Droplet impact and coalescence have been investigated by high-speed particle image velocimetry. Velocity fields near the liquid-substrate interface have been observed for the impact and coalescence of 2.4 mm diameter droplets of glycerol/water striking a flat transparent substrate in air. The experimental arrangement images the internal flow in the droplets from below the substrate with a high-speed camera and continuous laser illumination. Experimental results are in the form of digital images that are processed by particle image velocimetry and image processing algorithms to obtain velocity fields, droplet geometries, and contact line positions. Experimental results are compared with numerical simulations by the lattice Boltzmann method.
Fully analytic energy gradient in the fragment molecular orbital method
Authors: Nagata Takeshi , Brorsen Kurt , Fedorov Dmitri G. , Kitaura Kazuo , Gordon Mark S.
Published: March 2011

The Z-vector equations are derived and implemented for solving the response term due to the external electrostatic potentials, and the corresponding contribution is added to the energy gradients in the framework of the fragment molecular orbital (FMO) method. To practically solve the equations for large molecules like proteins, the equations are decoupled by taking advantage of the local nature of fragments in the FMO method and establishing the self-consistent Z-vector method. The resulting gradients are compared with numerical gradients for the test molecular systems: (H2O)64, alanine decamer, hydrated chignolin with the protein data bank (PDB) ID of 1UAO, and a Trp-cage miniprotein construct (PDB ID: 1L2Y). The computation time for calculating the response contribution is comparable to or less than that of the FMO self-consistent charge calculation. It is also shown that the energy gradients for the electrostatic dimer approximation are fully analytic, which significantly reduces the computational costs. The fully analytic FMO gradient is parallelized with an efficiency of about 98% on 32 nodes.
Experimental and theoretical investigations on the warm-up of a high-pressure mercury discharge lamp
Authors: Zalach J. , Araoud Z. , Charrada K. , Franke St. , Schoepp H. , Zissis G.
Published: March 2011

Modern high-pressure discharge lamps are forced to provide instant light and hot relight capabilities—if possible at lower power units. A detailed understanding of the warm-up of high-pressure discharge lamps is therefore required. Complex fluid model codes were developed for the past years including more and more processes like two-dimensional treatment of convection trying to provide a more comprehensive and consistent description of high-pressure discharge lamps. However, there is a lack of experimental data to examine the performance of these models. This work provides a very complete set of geometrical, electrical, spectroscopic, and thermographic data according to the warm-up of a high-pressure mercury discharge lamp that is compared to the results of a state of the art fluid code. Quantitative agreement is achieved for single parameters like wall temperatures. But the paper also reveals the need for further investigations and improvements of the code.
Formation of subwavelength grating on molybdenum mirrors using a femtosecond Ti:sapphire laser system operating at 10 Hz
Authors: Sharma Avnish Kumar , Smedley John , Tsang Thomas , Rao Triveni
Published: March 2011

We report formation of subwavelength surface grating over large surface area of molybdenum mirror by multiple irradiation of amplified femtosecond laser pulses from a homemade Ti:sapphire oscillator–amplifier laser system in a raster scan configuration. The laser system delivered 2 mJ, 80 fs duration laser pulses at a pulse repetition rate of 10 Hz. Various parameters such as pulse fluence, number of pulses, laser polarization, scan speed, and scan steps were optimized to obtain uniform subwavelength gratings. Energy dispersive x-ray spectroscopy measurements were conducted to analyze the elemental composition of mirror surfaces before and after laser treatment.
Effect of poloidal asymmetry on the impurity density profile in tokamak plasmas
Authors: Fülöp T. , Moradi S.
Published: March 2011

The effect of poloidal asymmetry of impurities on impurity transport driven by electrostatic turbulence in tokamak plasmas is analyzed. It is found that if the density of the impurity ions is poloidally asymmetric then the zero-flux impurity density gradient is significantly reduced and even a sign change in the impurity flux may occur if the asymmetry is sufficiently large. This effect is most effective in low shear plasmas with the impurity density peaking on the inboard side and may be a contributing factor to the observed outward convection of impurities in the presence of radio frequency heating.
Cold and ultracold NH–NH collisions: The field-free case
Authors: Janssen Liesbeth M. C. , Żuchowski Piotr S. , van der Avoird Ad , Hutson Jeremy M. , Groenenboom Gerrit C.
Published: March 2011

We present elastic and inelastic spin-changing cross sections for cold and ultracold NH(X 3Σ−) + NH(X 3Σ−) collisions, obtained from full quantum scattering calculations on an accurate ab initio quintet potential-energy surface. Although we consider only collisions in zero field, we focus on the cross sections relevant for magnetic trapping experiments. It is shown that evaporative cooling of both fermionic 14NH and bosonic 15NH is likely to be successful for hyperfine states that allow s-wave collisions. The calculated cross sections are very sensitive to the details of the interaction potential, due to the presence of (quasi)bound state resonances. The remaining inaccuracy of the ab initio potential-energy surface therefore gives rise to an uncertainty in the numerical cross-section values. However, based on a sampling of the uncertainty range of the ab initio calculations, we conclude that the exact potential is likely to be such that the elastic-to-inelastic cross-section ratio is sufficiently large to achieve efficient evaporative cooling. This likelihood is only weakly dependent on the size of the channel basis set used in the scattering calculations.
TiN
x
/
HfO
2
interface dipole induced by oxygen scavenging
Authors: Afanas’ev V. V. , Stesmans A. , Pantisano L. , Cimino S. , Adelmann C. , Goux L. , Chen Y. Y. , Kittl J. A. , Wouters D. , Jurczak M.
Published: March 2011

Electron barrier height measurements at TiNx/HfO2 interfaces in metal-insulator-metal structures using internal photoemission of electrons reveal a significant (≈1 eV, i.e., about 1/3 of the total barrier height) influence of the opposite electrode material, i.e., Hf versus TiNx. This effect is suggested to be caused by oxygen scavenging from HfO2 by the opposite Hf electrode resulting in generation of positive charges in the oxide above the metal electrode surfaces. Such a considerable interface dipole component demonstrates a principle that may be used to tune the barrier.
A triboelectric x-ray source
Authors: Hird J. R. , Camara C. G. , Putterman S. J.
Published: March 2011

A source of x-rays capable of exciting the characteristic emission lines of Mo and Ag is demonstrated. The device, which requires no external high voltage supply, uses the triboelectric effect to produce a charge imbalance when silicone and a metal-loaded epoxy are made to repeatedly contact each other in vacuum. This provides a source of 40 keV electrons which generate bremsstrahlung and characteristic x-rays at a rate of >105 per contact cycle. By increasing the repetition rate of the contact cycle the viability of a device that emits 108 x-ray photons per second is suggested, making triboelectricity an inexpensive source of x-rays. The form factors and simplicity of such devices open up interesting possibilities for x-ray imaging.
Sb-doping of ZnO: Phase segregation and its impact on p-type doping
Authors: Friedrich F. , Sieber I. , Klimm C. , Klaus M. , Genzel Ch. , Nickel N. H.
Published: March 2011

The incorporation of antimony (Sb) in pulsed-laser deposited ZnO thin-films was investigated employing scanning electron microscopy, Raman spectroscopy, energy dispersive x-ray spectroscopy, and x-ray diffraction (XRD) measurements. It is shown that an increase in the Sb concentration in the target leads to a significant deterioration of the sample structure which is accompanied by a decrease in the deposition rate. Furthermore, the dopant transfer factor depends strongly on the deposition temperature and exhibits a steplike behavior above 600 °C. XRD measurements clearly show that significant Sb–O phase precipitations occur. The implications of our data on p-type doping of ZnO are discussed.
Enhancing the electron mobility of SrTiO3 with strain
Authors: Jalan Bharat , Allen S. James , Beltz Glenn E. , Moetakef Pouya , Stemmer Susanne
Published: March 2011

We demonstrate, using high-mobility SrTiO3 thin films grown by molecular beam epitaxy, that stress has a pronounced influence on the electron mobility in this prototype complex oxide. Moderate strains result in more than 300% increases in the electron mobilities with values exceeding 120 000 cm2/V s and no apparent saturation in the mobility gains. The results point to a range of opportunities to tailor high-mobility oxide heterostructure properties and open up ways to explore oxide physics.
Enhanced field-driven domain-wall motion in Pt/Co68B32/Pt strips
Authors: Lavrijsen R. , Verheijen M. A. , Barcones B. , Kohlhepp J. T. , Swagten H. J. M. , Koopmans B.
Published: March 2011

It is now commonly accepted that materials exhibiting high perpendicular magnetic anisotropy are excellent candidates for devices based on current-induced domain-wall (DW) motion. A major hindrance of these materials however, is that they exhibit strong DW pinning. Here we report a significant increase in the field-driven DW velocity in Pt(4 nm)/Co68B32(0.6 nm)/Pt(2 nm) layers patterned into 900 nm wide strips. We compare the DW velocity between Co and Co68B32 films and discuss the observed effects using the morphology of the films investigated by high-resolution transmission electron microscopy.
Universality of the spin pumping in metallic bilayer films
Authors: Yoshino T. , Ando K. , Harii K. , Nakayama H. , Kajiwara Y. , Saitoh E.
Published: March 2011

We show a clear guideline for generating a large spin current using the spin pumping in metallic bilayer films. We measured spin currents generated by the spin pumping in Ni1−xFex/Pt bilayer films using the inverse spin-Hall effect (ISHE). The magnitude of the ISHE signals are well reproduced by a calculation based on the model of the spin pumping. The result shows that the amplitude of a spin current is universally determined by the product of the saturation magnetization, the additional damping constant, and the solid angle of the magnetization precession.
Robust gigahertz fiber quantum key distribution
Authors: Clarke Patrick J. , Collins Robert J. , Hiskett Philip A. , Townsend Paul D. , Buller Gerald S.
Published: March 2011

We present recent results on an innovative fiber based short wavelength gigahertz clock rate quantum key distribution system operating over a standard telecommunications optical fiber quantum channel. This system is designed to be robust against environmentally induced changes in the polarization evolution of the photons in the optical fiber quantum channel and against path-length drift in the interferometers which could otherwise compromise system performance. Experimental results are presented for error rate, net bit rate and stability for different silicon single-photon avalanche diode detector types.
Magnetic properties of Pr0.7Ca0.3MnO3/SrRuO3 superlattices
Authors: Ziese M. , Vrejoiu I. , Pippel E. , Nikulina E. , Hesse D.
Published: March 2011

High-quality Pr0.7Ca0.3MnO3/SrRuO3 superlattices were fabricated by pulsed laser deposition and were investigated by high-resolution transmission electron microscopy and superconducting quantum interference device magnetometry. Superlattices with orthorhombic and tetragonal SrRuO3 layers were investigated. The superlattices grew coherently; in the growth direction Pr0.7Ca0.3MnO3 layers were terminated by MnO2 and SrRuO3 layers by RuO2-planes. All superlattices showed antiferromagnetic interlayer coupling in low magnetic fields. The coupling strength was significantly higher for orthorhombic than for tetragonal symmetry of the SrRuO3 layers. The strong interlayer exchange coupling in the superlattice with orthorhombic SrRuO3 layers led to a magnetization reversal mechanism with a partially inverted hysteresis loop.
Power scalability and frequency agility of compact terahertz source based on frequency mixing from solid-state lasers
Authors: Zhao Pu , Ragam Srinivasa , Ding Yujie J. , Zotova Ioulia B.
Published: March 2011

We investigate power scalability and frequency agility of a terahertz (THz) source by mixing two frequencies generated by solid-state lasers in a nonlinear crystal. They are made possible by introducing two solid-state laser crystals sharing the same Q switch and output coupler with the same laser beams decoupled to each other by a polarizer. Following the optimization, we have improved the THz output power nearly fivefold at 1.64 THz. By replacing one of the neodymium-doped lithium yttrium fluoride crystals with a neodymium-doped yttrium aluminum garnet crystal, we have produced 2.1 μW at 2.98 THz.
Enhancement of local electrical conductivities in SiC by femtosecond laser modification
Authors: Deki Manato , Ito Takuto , Yamamoto Minoru , Tomita Takuro , Matsuo Shigeki , Hashimoto Shuichi , Kitada Takahiro , Isu Toshiro , Onoda Shinobu , Ohshima Takeshi
Published: March 2011

Enhancement of local electric conductivities induced by femtosecond laser modification in silicon carbide was studied. Current-voltage (I-V) characteristics of the laser-modified regions were measured between the ion-implanted metal contacts. Interestingly, the resistance sharply decreased in the fluence range from 5.0 to 6.7 J/cm2. The resistance at the irradiation fluence of 53 J/cm2 decreased by more than six orders of magnitude compared with the nonirradiated one. From the I-V characteristics and the scanning electron microscope observations, we conclude that the phase separation associate with the formation of classical laser induced periodic structure causes the drastic increase in electric conductivity.
Ultracold O2 + O2 collisions in a magnetic field: On the role of the potential energy surface
Authors: Pérez-Ríos Jesús , Campos-Martínez José , Hernández Marta I.
Published: March 2011

The collision dynamics of 17\documentclass[12pt]{minimal}\begin{document}$\text{O}_2(^3\Sigma _g^-) + ^{17}\text{O}_2(^3\Sigma _g^-)$\end{document}O2(3Σg−)+17O2(3Σg−) in the presence of a magnetic field is studied within the close-coupling formalism in the range between 10 nK and 50 mK. A recent global ab initio potential energy surface (PES) is employed and its effect on the dynamics is analyzed and compared with previous calculations where an experimentally derived PES was used [T. V. Tscherbul et al., New J. Phys 134, 055021 (2009)]. Compared to the results using the older PES, magnetic-field dependence of the low-field-seeking state in the ultracold regime is characterized by a very large background scattering length, abg, and cross sections exhibit broader and more pronounced Feshbach resonances. The marked resonance structure is somewhat surprising considering the influence of inelastic scattering but it can be explained by resorting to the analytical van der Waals theory, where the short-range amplitude of the entrance channel wavefunction is enhanced by the large abg. This strong sensitivity to the short range of the ab initio PES persists up to relatively high energies (10 mK). After this study and despite quantitative predictions are very difficult, it can be concluded that the ratio between elastic and spin relaxation scattering is generally small, except for magnetic fields which are either low or close to an asymmetric Fano-type resonance. Some general trends found here, such as a large density of quasibound states and a propensity toward large scattering lengths, could be also characteristic of other anisotropic molecule–molecule systems.
Droplet spreading using low frequency vibration
Authors: Whitehill James , Neild Adrian , Ng Tuck Wah , Martyn Steven , Chong Jonathan
Published: March 2011

Low frequency actuation is known to cause the oscillatory movement of contact lines in droplets. Here, the linear relation between contact line location and oscillation is broken when high amplitudes of actuation are used to accomplish spreading. This spreading is able to occur on widely used surfaces, and can cause the contact angle to fall well below receding angles over the whole actuation cycle. This mechanism portends use in applications that require the imaging of multiple droplets evenly spread across a defined area and for adjacent droplets to spread, meet and mix via acoustic streaming.
Communication: Single crystal x-ray diffraction observation of hydrogen bonding between 1-propanol and water in a structure II clathrate hydrate
Authors: Udachin Konstantin , Alavi Saman , Ripmeester John A.
Published: March 2011

Single crystal x-ray crystallography is used to detect guest–host hydrogen bonding in structure II (sII) binary clathrate hydrate of 1-propanol and methane. X-ray structural analysis shows that the 1-propanol oxygen atom is at a distance of 2.749 and 2.788 Å from the closest clathrate hydrate water oxygen atoms from a hexagonal face of the large sII cage. The 1-propanol hydroxyl hydrogen atom is disordered and at distances of 1.956 and 2.035 Å from the closest cage water oxygen atoms. These distances are compatible with guest–water hydrogen bonding. The C–C–C–O torsional angle in 1-propanol in the cage is 91.47° which corresponds to a staggered conformation for the guest. Molecular dynamics studies of this system demonstrated guest–water hydrogen bonding in this hydrate. The molecular dynamics simulations predict most probable distances for the 1-propanol–water oxygen atoms to be 2.725 Å, and the average C–C–C–O torsional angle to be ∼59° consistent with a gauche conformation. The individual cage distortions resulting from guest–host hydrogen bonding from the simulations are rather large, but due to the random nature of the hydrogen bonding of the guest with the 24 water molecules making up the hexagonal faces of the large sII cages, these distortions are not observed in the x-ray structure.
Understanding Design as a Multiagent Coordination Process: Distribution, Complexity, and Emergence
Authors: Alexiou Katerina
Published: March 2011

Design is increasingly perceived as a social process that involves the participation of multiple agents with multiple, and often conflicting, needs, knowledge, and goals. It is proposed here that the notion of coordination is an apposite concept for capturing the social distributed character of design and for reconciling social and cognitive perceptions of design activity. Coordination places emphasis on issues of interdependency, complexity, and distribution, and facilitates the understanding of design by including notions of collaboration as well as conflict. Additionally, coordination is used to capture the generative, creative aspects of design. In this study I use insights from complexity science to offer an understanding of coordination as a process that entails the emergence of collective design solutions.
Evaluating the Role of Participation in Modeling Studies for Environmental Planning
Authors: Wassen Martin J , Runhaar Hens , Barendregt Aat , Okruszko Tomasz
Published: March 2011

Stakeholder participation in modeling studies is often advocated as a means to enhance the acceptability of these studies. In turn, acceptability of modeling studies is considered as an important factor stimulating their actual use in policy making. Although these hypotheses are generally accepted, to date little empirical evidence is available to support or reject them. This study aims at exploring in more detail whether or not stakeholder participation increases acceptability of modeling studies and the use of their results in policy making, and how that can be understood. For this purpose thirteen projects were analyzed. Methods employed included a review of project reports and further papers on the project, as well as standardized surveys with scientists involved in the cases and open oral interviews with other key figures. A majority of the projects concerned European cases in which land use and exploitation of water resources had to be planned in combination. Our results suggest that acceptability of modeling studies is correlated to the actual use of these studies, although it does not seem to be a prerequisite. In turn, acceptability of modeling studies is positively correlated to a participatory approach. The latter is also correlated to the extent to which policy-oriented learning took place during modeling studies. In addition our study shows that stakeholder participation enhances acceptability of the models by allowing stakeholders to contribute ideas, knowledge, and priorities. Also communication of studies and their results to stakeholders is important for the acceptability of models. Finally, applicability of models seems to be a prerequisite for their acceptability. No evidence was found of the acceptability of models being positively influenced by the model's credibility, the extent to which models reduce uncertainties, the insights that models give into the effects of policies, the transparency of models and modeling studies, nor the extent to which they facilitate a mutual understanding of actors with conflicting interests. We recommend further testing of the general validity of our conclusions by evaluating other projects.
Compactness and Connection in Environmental Design: Insights from Ecoburbs and Ecocities for Design with Nature
Authors: Crewe Katherine , Forsyth Ann
Published: March 2011

It is widely agreed that planners should be aiming to create cities that are more ecologically sensitive. Governments, developers, planners, and designers almost everywhere claim to be doing just that. What does this mean, however? We argue that planners have been promoting a compact and efficient approach to green development, on the basis of a comprehensive yet evolving understanding of environmental systems. There is an alternative approach, however, more firmly based in psychological and human perceptions of nature. With popular appeal, as well as academic and professional roots in landscape architecture and environmental psychology, this connective approach stresses human connection to nature at a local scale. These represent distinctly different approaches to ecologically sensitive development and quite different priorities about which ecological processes are most important. Case studies of the Woodlands, Village Homes, Civano, Almere, Hammarby Sjöstad, and Sydney Olympic Park demonstrate these issues. Planners will need to make some difficult choices not only between more and less ecologically sensitive designs but also between competing ecological values.
Dynamics of Periurban Spatial Structures: Investigating Differentiated Patterns of Change on Oporto's Urban Fringe
Authors: Serra Miguel , Pinho Paulo
Published: March 2011

In this paper we describe the evolution of the urban grids of five case studies from the urban fringe of the Oporto Metropolitan Area throughout the last fifty years. We use a cartographic redrawing technique to recreate their street networks at four different historical moments and space syntax to explore their configurational evolution. Besides the confirmation of space syntax as a particularly relevant tool for the analysis and planning of peripheral urban areas, the study clarifies the configurational differences between rural and urban grids, provides evidence of different suburban growth patterns, and demonstrates strong relationships between such patterns and the evolution of the system's syntactic intelligibility.
An Assessment of the Effectiveness of Multiple Hypothesis Testing for Geographical Anomaly Detection
Authors: Brunsdon Chris , Charlton Martin
Published: March 2011

The practice of multiple significance testing is reviewed, and an alternative to the frequently used Bonferroni correction is considered. Rather than controlling the family-wise error rate (FWER)—the probability of a false positive in any of the significance tests—this alternative due to Benjamini and Hochberg controls the false discovery rate (FDR). This is the proportion of tests reporting a significant result that are actually ‘false alarms’. The methods (and some variants) are demonstrated on a procedure to detect clusters of full-time unpaid carers based on UK census data, and are also assessed using simulation. Simulation results show that the FDR-based corrections are typically more powerful than FWER-based ones, and also that the degree of conservatism in FWER-based procedures is quite extreme, to the extent that the standard Bonferroni procedure intended to constrain the FWER to be below 0.05 actually has a FWER of around 6 × 10−5. We conclude that in situations where one is scanning for anomalies, the extreme conservatism of FWER-based approaches results in a lack of power, and that FDR-based approaches are more appropriate.
On Why Planning Should Not Reinforce Self-Reinforcing Trends: A Cautionary Analysis of the Compact-City Proposal Applied to Large Cities
Authors: Ferreira António , Batey Peter
Published: March 2011

Urban densification has been presented as a general recipe to reduce travelling. The size of settlements was not considered particularly relevant in this proposal. Two arguments are presented that challenge the notion that densification of large cities leads to less travelling. The first is related to the internal dynamics of compact areas in large cities; the second to the dynamics between central and peripheral areas. It is shown that the densification of large cities leads to either more travelling because of the wide range of available opportunities provided by agglomeration effects, or more time spent on travelling due to congestion. The conclusion is that it is counterproductive for transport planning to endorse approaches that compact the urban form of large cities.
Negotiating Constraints to the Adoption of Agent-Based Modeling in Tourism Planning
Authors: Johnson Peter A , Sieber Renee E
Published: March 2011

Recent work exploring the use of agent-based models (ABMs) in a planning support role must be accompanied by an evaluation of the possible constraints that exist to the use of these models. This research presents an evaluation, from the perspective of professional tourism planners, of the potential for ABM of tourism dynamics to serve as a planning support system (PSS). Tourism is a phenomenon that is inherently individually based, with many interacting processes occurring at multiple scales, across space and time. This makes it a natural environment in which to test an ABM-based PSS. We conducted a series of interviews with tourism planners operating in the Canadian province of Nova Scotia, a region where tourism plays an important economic role. These interviews consisted of a general-needs overview, coupled with an assessment of a prototype model we developed, called TourSim. The interviews sought to uncover the specific planning tasks to which ABM would be best applied and identify areas of adoption constraint. The results of this research indicate that TourSim served as a scenario development tool, with a focus on data analysis and communication. Conversely, TourSim was reported to lack transparency, which affected the confidence that planners had in its results. This evaluation clarifies the path forward for developers looking to introduce ABM to planning practice.
Are Engineering Reasons Zoning Neutral? An Empirical Inquiry into Development Proposals in Green Belt and Agriculture Zones
Authors: Lai Lawrence Wai Chung , Wong Kelvin Siu Kei , Chau Kwong Wing
Published: March 2011

As a first statistical study of a planning authority's reasons for rejecting development proposals, this study examines hydraulic and transport engineering reasons adopted by the Town Planning Board for dismissing development applications for ‘small house’ use in Green Belt and Agriculture Zones in Hong Kong to verify the hypothesis that both hydraulic and traffic matters are not zoning-class dependent. The findings, from contingency table analysis of 127 sets of official nonaggregate planning data over a period of more than eight years, appear to affirm the supposition that engineering reasoning has not been swayed by nontechnical planning considerations in either the Green Belt or Agriculture Zones. However, a textual analysis of the objections from all available government records suggests that policy concerns broader than technical considerations were in fact decisive. The study sheds light on the mode of use of technocratic considerations in public policy decision making and articulates with the concept of zone separation based on the Coase theorem.
Acacia seedling morphology: phyllotaxy and its relationship to seed mass
Authors: Miller Joseph T. , Miller Cathy
Published: March 2011

Acacia, with over 1000 species, is the largest plant genus in Australia and is distributed throughout most of the continent. This work investigates seed mass and seedling phyllotaxy development in 287 species of this genus to better understand these important ecological and taxonomic traits. Seed mass varied over 100-fold with an average mass of 17.9 (range 2.1–308) mg per seed. Two common forms of seedling phyllotaxy were seen. The most common seedling development type displayed a pinnate first leaf with an alternate, bipinnate second leaf (pinnate : bipinnate). In the less common form, the first two leaves were pinnate and opposite each other (pinnate : pinnate). When compared with the phylogenetic tree of Acacia, the pinnate : pinnate state is more commonly resolved in taxa found at the basal nodes of the tree, but not exclusively. Overall, species with heavier seeds have more seedling leaflet pairs and pinnules. However, it was also found that the pinnate : bipinnate seedlings had more first leaf leaflet pairs than the pinnate : pinnate form. The pinnate : pinnate plants had an identical number of leaflet pairs on their first and second leaves. The number of leaflet pairs on the first leaf was highly correlated with the number of pinnules on a leaflet of the second leaf on the pinnate : bipinnate form. We discuss the phyllotactic variation within the Acacia phylogenetic context and possible developmental processes.