bluuebunny/crossref_metadata_2025 huggingface dataset:
Paradigmenwechsel in der sog. „gesundheitlichen Eignung“ von neu einzustellenden Beamtinnen und Beamten
Authors: Lange R.
Published: April 2014

Das Bundesverwaltungsgericht hat in aktueller Rechtsprechung den Maßstab für die „gesundheitliche Eignung“ von neu einzustellenden Beamtinnen und Beamten wesentlich abgesenkt. Für die vorgeschriebene amtsärztliche Einstellungsuntersuchung bedeutet dies, dass bei kritischen Fällen eine Empfehlung zur Nichteinstellung mangels belastbarer, d. h. trennscharfer wissenschaftlicher Grundlagen kaum noch in Frage kommt. Damit entfällt weitgehend die vormals beamtenrechtlich angestrebte Filterwirkung. Auch wenn dieser weit eröffnete Zugang zum Beamtenstatus für die gesundheitlich vorbelasteten Interessenten erfreulich sein mag, so sind die nachfolgenden Auswirkungen auf dienstlich-organisatorische wie auch auf fiskalische Aspekte (Beihilfen, Versorgungslasten) schwer absehbar. Die amtsärztliche Einstellungsuntersuchung wird daher zukünftig einen zunehmenden Schwerpunkt in einer Beratung über die möglicher Weise zu berücksichtigenden Verwendungsbeschränkungen der zuzulassenden Bewerberinnen und Bewerber entwickeln.
Identification of Markov process within a wind turbine array boundary layer
Authors: Melius Matthew S. , Tutkun Murat , Cal Raúl Bayoán
Published: April 2014

The Markovian properties within a wind turbine array boundary layer are explored for data taken in a wind tunnel containing a model wind turbine array. A stochastic analysis of the data is carried out using the mathematics of Markov processes. The data were obtained using hot-wire anemometry thus providing point velocity statistics. The theory of Markov process is applied to obtain a statistical description of longitudinal velocity increments inside the turbine wake. Comparison of two- and three-scale conditional probability density functions indicates the existence of Markovian properties in longitudinal velocity increments for scale differences larger than the Taylor microscale. This result is quantified by use of the Wilcoxon rank-sum test which verifies that this relationship holds independent of initial scale selection outside of the near-wake region behind a wind turbine. Furthermore, at the locations which demonstrate Markovian properties, there appears to be a well defined inertial subrange which follows Kolmogorov's −5/3 scaling behavior. The results show that directly behind the tips of the rotor and the hub, the complex turbulent interactions and large scale structures of the near-wake affect the Markovian nature of the field. The presence of a Markov process in the remaining locations leads to characterization of the development multiscale statistics of the wind turbine wakes using the most recent states of the flow.
A new dual-plate slipometer for measuring slip between molten polymers and extrusion die materials
Authors: Schmalzer A. M. , Giacomin A. J.
Published: April 2014

In this work, we study the slip behaviors common to plastics die extrusion metals or platings using a new instrument called a dual-plate slipometer. By dual-plate, we mean that whereas the stationary plate incorporates a local shear stress transducer, the moving plate does not. The stationary plate and transducer are made of one stainless steel, but the moving plate is made from, or plated with, different extrusion die materials under study. This new instrument allows slip velocity to be measured without having to build a new shear stress transducer from each extrusion metal or plating under study. We explore the effect of extrusion die composition and die metal surface morphology on the slip properties of polyolefins using a sliding plate rheometer. In this work, we studied the slip behaviors of polyolefins on four common plastics die extrusion metals or platings, without having to build a new shear stress transducer from each. Specifically, our new method replaces the moving plate; with each of the four die metals or platings under study without changing the stainless steel material of the shear stress transducer and its stationary plate. Our experiments include high-density polyethylene, low-density polyethylene, and polypropylene (PP) on four different die metals or platings. We use steady simple shear to obtain shear stress versus nominal shear rate for different gaps, from which we can then deduce the slip velocity using the Mooney analysis. We then fit four slip models to our experimental measurements, and we find the Hatzikiriakos hyperbolic sine model to be accurate, even for the measured inflections in the slip velocity as a function of shear stress curves. Our analysis includes detailed characterization of the die metal plating surfaces, including measurements of the composition of the sliding plates by energy dispersive spectroscopy, surface energy by contact angle goniometry, and surface roughness by both white light interference and stylus profilometries. We use our slip measurements to evaluate the Allal-Vergnes equation for the critical shear stress for slip [A. Allal and B. Vergnes, “Effect of die surface on the onset of stick-slip transition in the flow of molten linear polymers,” J. Non-Newtonian Fluid Mech. 167–168, 46–49 (2012)]. We conclude our analysis by dedimensionalizing slip, and we then use these dimensionless groups to analyze slip. This paper provides a set of reference data for extrusion die designers for polyolefins.
Effects, determination, and correction of count rate nonlinearity in multi-channel analog electron detectors
Authors: Reber T. J. , Plumb N. C. , Waugh J. A. , Dessau D. S.
Published: April 2014

Detector counting rate nonlinearity, though a known problem, is commonly ignored in the analysis of angle resolved photoemission spectroscopy where modern multichannel electron detection schemes using analog intensity scales are used. We focus on a nearly ubiquitous “inverse saturation” nonlinearity that makes the spectra falsely sharp and beautiful. These artificially enhanced spectra limit accurate quantitative analysis of the data, leading to mistaken spectral weights, Fermi energies, and peak widths. We present a method to rapidly detect and correct for this nonlinearity. This algorithm could be applicable for a wide range of nonlinear systems, beyond photoemission spectroscopy.
Exciplex emission and decay of co-deposited 4,4′,4″-tris[3-methylphenyl(phenyl)amino]triphenylamine:tris-[3-(3-pyridyl)mesityl]borane organic light-emitting devices with different electron transporting layer thicknesses
Authors: Huang Qingyu , Zhao Suling , Xu Zheng , Fan Xing , Shen Chongyu , Yang Qianqian
Published: April 2014

Highly efficient fluorescence organic light-emitting diodes (OLEDs) based on the mixed 4,4′,4″-tris[3-methylphenyl(phenyl)amino]triphenylamine:tris-[3-(3-pyridyl)mesityl]borane (1:1) system are reported. The electroluminescence due to the exciplex emission is red shifted when the thickness of the electron-transporting layer increases. The prepared OLEDs achieve a low turn-on voltage of 2.1 V, a high current efficiency of 36.79 cd/A, and a very high luminescence of 17 100 cd/m2, as well as a low efficiency roll-off. The current efficiency of the optimized OLED is maintained at more than 28.33 cd/A up to 10 000 cd m−2. The detailed recombination mechanism of the prepared OLEDs is investigated by the transient electroluminescence method. It is concluded that there are no contributions from trapped charges and annihilations of triplet-triplet excitons to the detected electroluminescence.
Propulsive performance of unsteady tandem hydrofoils in a side-by-side configuration
Authors: Dewey Peter A. , Quinn Daniel B. , Boschitsch Birgitt M. , Smits Alexander J.
Published: April 2014

Experimental and analytical results are presented on two identical bio-inspired hydrofoils oscillating in a side-by-side configuration. The time-averaged thrust production and power input to the fluid are found to depend on both the oscillation phase differential and the transverse spacing between the foils. For in-phase oscillations, the foils exhibit an enhanced propulsive efficiency at the cost of a reduction in thrust. For out-of-phase oscillations, the foils exhibit enhanced thrust with no observable change in the propulsive efficiency. For oscillations at intermediate phase differentials, one of the foils experiences a thrust and efficiency enhancement while the other experiences a reduction in thrust and efficiency. Flow visualizations reveal how the wake interactions lead to the variations in propulsive performance. Vortices shed into the wake from the tandem foils form vortex pairs rather than vortex streets. For in-phase oscillation, the vortex pairs induce a momentum jet that angles towards the centerplane between the foils, while out-of-phase oscillations produce vortex pairs that angle away from the centerplane between the foils.
Interpretation of the accidental predissociation of the E1Π state of CO
Authors: Majumder M. , Sathyamurthy N. , Vázquez G. J. , Lefebvre-Brion H.
Published: April 2014

A special case of predissociation, known as indirect or accidental predissociation observed in the Rydberg E1Π bound state of CO is discussed. We resort to ab initio potentials in order to determine the plausible mechanism for this predissociation. Values of the predissociation width for the valence k3Π state of CO, as obtained from Fermi's golden rule, are also reported. The predissociation width obtained for the mixed E1Π (v = 1, J = 7) state is 0.033 cm−1 compared to the experimental value of 0.034 cm−1. The mixed E − E′ state with J = 28, v = 0 is found to be in near resonance condition with the k3Π (v = 4, J = 28) state, thus providing the means to indirect predissociation.
Increasing the applicability of density functional theory. IV. Consequences of ionization-potential improved exchange-correlation potentials
Authors: Verma Prakash , Bartlett Rodney J.
Published: April 2014

This paper's objective is to create a “consistent” mean-field based Kohn-Sham (KS) density functional theory (DFT) meaning the functional should not only provide good total energy properties, but also the corresponding KS eigenvalues should be accurate approximations to the vertical ionization potentials (VIPs) of the molecule, as the latter condition attests to the viability of the exchange-correlation potential (VXC). None of the prominently used DFT approaches show these properties: the optimized effective potential VXC based ab initio dftdoes. A local, range-separated hybrid potential cam-QTP-00 is introduced as the basis for a “consistent”KS DFT approach. The computed VIPs as the negative of KS eigenvalue have a mean absolute error of 0.8 eV for an extensive set of molecule's electron ionizations, including the core. Barrier heights, equilibrium geometries, and magnetic properties obtained from the potential are in good agreement with experiment. A similar accuracy with less computational efforts can be achieved by using a non-variational global hybrid variant of the QTP-00 approach.
Hierarchy of model Kohn–Sham potentials for orbital-dependent functionals: A practical alternative to the optimized effective potential method
Authors: Kohut Sviataslau V. , Ryabinkin Ilya G. , Staroverov Viktor N.
Published: April 2014

We describe a method for constructing a hierarchy of model potentials approximating the functional derivative of a given orbital-dependent exchange-correlation functional with respect to electron density. Each model is derived by assuming a particular relationship between the self-consistent solutions of Kohn–Sham (KS) and generalized Kohn–Sham (GKS) equations for the same functional. In the KS scheme, the functional is differentiated with respect to density, in the GKS scheme—with respect to orbitals. The lowest-level approximation is the orbital-averaged effective potential (OAEP) built with the GKS orbitals. The second-level approximation, termed the orbital-consistent effective potential (OCEP), is based on the assumption that the KS and GKS orbitals are the same. It has the form of the OAEP plus a correction term. The highest-level approximation is the density-consistent effective potential (DCEP), derived under the assumption that the KS and GKS electron densities are equal. The analytic expression for a DCEP is the OCEP formula augmented with kinetic-energy-density-dependent terms. In the case of exact-exchange functional, the OAEP is the Slater potential, the OCEP is roughly equivalent to the localized Hartree–Fock approximation and related models, and the DCEP is practically indistinguishable from the true optimized effective potential for exact exchange. All three levels of the proposed hierarchy require solutions of the GKS equations as input and have the same affordable computational cost.
Second-order model of entrainment in planar turbulent jets at low Reynolds number
Authors: Paillat S. , Kaminski E.
Published: April 2014

Turbulent jets and plumes are commonly encountered in natural and industrial environments, and have been the objects of seminal works on turbulent free shear flows. The dynamics of turbulent jets is most often described as a function of the so-called entrainment coefficient, α, which quantifies the entrainment of ambient fluid into the jets. This key parameter has been determined in numerous and extensive experimental, numerical, and theoretical studies of axisymmetric jets. However, data remain scarce on turbulent planar jets. Available studies have shown that at low distance from the source, α increases with the source Reynolds number, and that α increases with distance from the source for large source Reynolds number. But no link has been made between these two kinds of observation so far. To study the relative influence of source Reynolds number, Re0, and distance from source on entrainment in planar turbulent jets, we perform new experiments at low Re0 (between 59 and 424) with three different aspect ratio (185, 370, and 925) and at small and large distances from the source. Our experimental results show no systematic variations of α as a function of Re0 or as a function of the distance from the source. To interpret these observations, we develop a formalism based on the flow velocity profiles, which yields an expression of α as a function of the evolution of the Reynolds shear stress and of the turbulent fluctuations of the radial and vertical velocities. We obtain that the main contribution to entrainment is related to the turbulent shear stress, and that second-order fluctuations of the velocity account for the observed variations of α. The evolution to a fully self-similar regime in which these fluctuations are fully negligible is too slow at small Re0 for this regime to be observed in our experiments, even at the largest distances from the source.
Homogeneous carbon doping of magnesium diboride by high-temperature, high-pressure synthesis
Authors: Susner M. A. , Bohnenstiehl S. D. , Dregia S. A. , Sumption M. D. , Yang Y. , Donovan J. J. , Collings E. W.
Published: April 2014

We have used high-pressure, high-temperature synthesis at 1500–1700 °C and 10 MPa to create homogeneously C-substituted MgB2 from a B4C + Mg mixture. X-ray diffraction analysis showed large peak-shifts consistent with a decrease in the a lattice parameter for the B4C-derived MgB2 as compared to an undoped sample (0.033–0.037 Å, depending on the sample). Microstructural investigation showed a three-phase mixture in the B4C-derived ingots: MgB2−xCx (with 0.178 < x < 0.195), MgB2C2, and Mg. The carbon concentration determined from the lattice parameter shift (5.95 at. %) matched well with the calorimetrically derived concentration of 5.3–5.8 at. % C. Furthermore, the carbon content measured by electron probe micro-analysis was shown to be 6.2 ± 1.3 at. %. Finally, we performed bulk specific heat measurements to determine the homogeneity of C-doping in the MgB2. The width of the Tc distribution for the C-doped MgB2 was only 3–6 K with a full-width half maximum (FWHM) of 1.4 K, compared to a width of 2.5 K and a FWHM of 0.65 for an undoped sample. The consistency of these three measurements on a large-grained homogeneous material is unambiguously supportive of C-substitution.
Using the electron localization function to correct for confinement physics in semi-local density functional theory
Authors: Hao Feng , Armiento Rickard , Mattsson Ann E.
Published: April 2014

We have previously proposed that further improved functionals for density functional theory can be constructed based on the Armiento-Mattsson subsystem functional scheme if, in addition to the uniform electron gas and surface models used in the Armiento-Mattsson 2005 functional, a model for the strongly confined electron gas is also added. However, of central importance for this scheme is an index that identifies regions in space where the correction provided by the confined electron gas should be applied. The electron localization function (ELF) is a well-known indicator of strongly localized electrons. We use a model of a confined electron gas based on the harmonic oscillator to show that regions with high ELF directly coincide with regions where common exchange energy functionals have large errors. This suggests that the harmonic oscillator model together with an index based on the ELF provides the crucial ingredients for future improved semi-local functionals. For a practical illustration of how the proposed scheme is intended to work for a physical system we discuss monoclinic cupric oxide, CuO. A thorough discussion of this system leads us to promote the cell geometry of CuO as a useful benchmark for future semi-local functionals. Very high ELF values are found in a shell around the O ions, and take its maximum value along the Cu–O directions. An estimate of the exchange functional error from the effect of electron confinement in these regions suggests a magnitude and sign that could account for the error in cell geometry.
Miniaturized high-precision piezo driven two axes stepper goniometer
Authors: Zhong H. , Schwarz A. , Wiesendanger R.
Published: April 2014

A miniaturized inertial stepper goniometer with two orthogonal axes (θ and φ axes) has been realized using four shear piezo based actuators arranged in a tetrahedral configuration tangent with a polished sapphire spherical rotor. The measured sensitivity is about 11.5 microdegree (μ°) per Volt. The smallest angular step size, achieved with a minimal peak-to-peak voltage Upp of 200 V is about 0.6 millidegree (m°). The crosstalk between both axes is below 10%. Our specific design is used to accurately position a glass fiber, but the concept can be utilized for many different applications as well.
Rotational modes in a phononic crystal with fermion-like behavior
Authors: Deymier P. A. , Runge K. , Swinteck N. , Muralidharan K.
Published: April 2014

The calculated band structure of a two-dimensional phononic crystal composed of stiff polymer inclusions in a soft elastomer matrix is shown to support rotational modes. Numerical calculations of the displacement vector field demonstrate the existence of modes whereby the inclusions and the matrix regions between inclusions exhibit out of phase rotations but also in phase rotations. The observation of the in-phase rotational mode at low frequency is made possible by the very low transverse speed of sound of the elastomer matrix. A one-dimensional block-spring model is used to provide a physical interpretation of the rotational modes and of the origin of the rotational modes in the band structure. This model is analyzed within Dirac formalism. Solutions of the Dirac-like wave equation possess a spinor part and a spatio-temporal part. The spinor part of the wave function results from a coupling between the senses (positive or negative) of propagation of the wave. The wave-number dependent spinor-part of the wave function for two superposed waves can impose constraints on the integral of the spatio-temporal part that are reflected in a fermion-like lifting of degeneracy in the phonon band structure associated with in-phase rotations.
Do temperature and nanoparticle size affect the thermal conductivity of alumina nanofluids?
Authors: Lee Ji-Hwan , Lee Seung-Hyun , Pil Jang Seok
Published: April 2014

This study investigates the effects of nanoparticle size and temperature on the thermal conductivity enhancement of water-based alumina (Al2O3) nanofluids, using the centrifuging method and relative centrifugal forces of differing magnitude to produce nanofluids of three different particles without dispersants and surfactants. We determined the coupling dependency in heat conduction enhancement relative to nanoparticle size and temperature of the alumina nanofluids and also experimentally showed that the effect of temperature on thermal conductivity is strongly dependent on nanoparticle size. Also, our experimental data presented that the effective medium theory models such as the Hashin and Shtrikman bounds are not sufficient to explain the thermal conductivity of nanofluids because they cannot account for the temperature- and size-dependent nature of water-based alumina nanofluids.
Responsive immunization and intervention for infectious diseases in social networks
Authors: Wu Qingchu , Zhang Haifeng , Zeng Guanghong
Published: April 2014

By using the microscopic Markov-chain approximation approach, we investigate the epidemic spreading and the responsive immunization in social networks. It is assumed that individual vaccination behavior depends on the local information of an epidemic. Our results suggest that the responsive immunization has negligible impact on the epidemic threshold and the critical value of initial epidemic outbreak, but it can effectively inhibit the outbreak of epidemic. We also analyze the influence of the intervention on the disease dynamics, where the vaccination is available only to those individuals whose number of neighbors is greater than a certain value. Simulation analysis implies that the intervention strategy can effectively reduce the vaccine use under the epidemic control.
Diffusion-induced periodic transition between oscillatory modes in amplitude-modulated patterns
Authors: Tang Xiaodong , He Yuxiu , Epstein Irving R. , Wang Qun , Wang Shaorong , Gao Qingyu
Published: April 2014

We study amplitude-modulated waves, e.g., wave packets in one dimension, overtarget spirals and superspirals in two dimensions, under mixed-mode oscillatory conditions in a three-variable reaction-diffusion model. New transition zones, not seen in the homogeneous system, are found, in which periodic transitions occur between local 1N−1 and 1N oscillations. Amplitude-modulated complex patterns result from periodic transition between (N − 1)-armed and N-armed waves. Spatial recurrence rates provide a useful guide to the stability of these modulated patterns.
Experimental evidence for collisional shock formation via two obliquely merging supersonic plasma jets
Authors: Merritt Elizabeth C. , Moser Auna L. , Hsu Scott C. , Adams Colin S. , Dunn John P. , Miguel Holgado A. , Gilmore Mark A.
Published: April 2014

We report spatially resolved measurements of the oblique merging of two supersonic laboratory plasma jets. The jets are formed and launched by pulsed-power-driven railguns using injected argon, and have electron density ∼1014 cm−3, electron temperature ≈1.4 eV, ionization fraction near unity, and velocity ≈40 km/s just prior to merging. The jet merging produces a few-cm-thick stagnation layer, as observed in both fast-framing camera images and multi-chord interferometer data, consistent with collisional shock formation [E. C. Merritt et al., Phys. Rev. Lett. 111, 085003 (2013)].
Three-dimensional analytic probabilities of coupled vibrational-rotational-translational energy transfer for DSMC modeling of nonequilibrium flows
Authors: Adamovich Igor V.
Published: April 2014

A three-dimensional, nonperturbative, semiclassical analytic model of vibrational energy transfer in collisions between a rotating diatomic molecule and an atom, and between two rotating diatomic molecules (Forced Harmonic Oscillator–Free Rotation model) has been extended to incorporate rotational relaxation and coupling between vibrational, translational, and rotational energy transfer. The model is based on analysis of semiclassical trajectories of rotating molecules interacting by a repulsive exponential atom-to-atom potential. The model predictions are compared with the results of three-dimensional close-coupled semiclassical trajectory calculations using the same potential energy surface. The comparison demonstrates good agreement between analytic and numerical probabilities of rotational and vibrational energy transfer processes, over a wide range of total collision energies, rotational energies, and impact parameter. The model predicts probabilities of single-quantum and multi-quantum vibrational-rotational transitions and is applicable up to very high collision energies and quantum numbers. Closed-form analytic expressions for these transition probabilities lend themselves to straightforward incorporation into DSMC nonequilibrium flow codes.
Performance evaluation, energy conservation potential, and parametric study of borehole heat exchanger for space cooling in building
Authors: Lal Shiv , Babu Balam Nagesh , Jain H. K.
Published: April 2014

A building integrated Borehole Heat Exchanger (BHE) has been designed and installed at Central Building Research Institute, Roorkee (29.87°N 77.88°E) India. The thermal performance and energy conservation potential (cooling potential) of installed BHE have been evaluated during summer months in the year 2013. The parametric study has also been done for its maximum performance. Quantitative assessment of CO2 mitigation has also been computed. The constant BHE water temperature (approximately 25 °C) witnessed the transferring of heat from air to water and vice-versa. It is found that the air temperature is reduced by 8–13 °C during summer season at air velocity of 18.9 m/s from the inlet of the BHE (exit of blower), whereas outdoor temperature was recorded as 35–39 °C. This system is capable of maintaining room temperature between 26 and 30 °C during peak summer season. The cooling capacity is evaluated between 150 and 180 kW h. BHE integrated with building can significantly reduce the 39836.25 kW h of electrical power needed for space cooling load and it can reduce global warming by substantially mitigating the carbon-dioxide to the tune of 50.10 tonnes annually. During the parametric study, it is found that double U-tube, circular pipe with optimum pitch of 4 in. is needed to achieve higher performance from the BHE.
Voltage-tunable terahertz and infrared photodetectors based on double-graphene-layer structures
Authors: Ryzhii V. , Otsuji T. , Aleshkin V. Ya. , Dubinov A. A. , Ryzhii M. , Mitin V. , Shur M. S.
Published: April 2014

We propose and theoretically substantiate the concept of terahertz and infrared photodetectors using the resonant radiative transitions between graphene layers (GLs) in double-GL structures. The calculated absorption spectrum and the spectral characteristics of the photodetector responsivity exhibit sharp resonant maxima at the photon energies in a wide range. The resonant maxima can be tuned by the applied voltage. We compare the photodetector responsivity with that of the GL p-i-n photodiodes and quantum-well infrared photodetectors. Weak temperature dependences of the photocurrent and dark current enable the effective operation of the proposed photodetector at room temperature.
Energy level alignment in polymer organic solar cells at donor-acceptor planar junction formed by electrospray vacuum deposition
Authors: Kim Ji-Hoon , Hong Jong-Am , Kwon Dae-Gyeon , Seo Jaewon , Park Yongsup
Published: April 2014

Using ultraviolet photoelectron spectroscopy (UPS), we have measured the energy level offset at the planar interface between poly(3-hexylthiophene) (P3HT) and C61-butyric acid methylester (PCBM). Gradual deposition of PCBM onto spin-coated P3HT in high vacuum was made possible by using electrospray vacuum deposition (EVD). The UPS measurement of EVD-prepared planar interface resulted in the energy level offset of 0.91 eV between P3HT HOMO and PCBM LUMO, which is considered as the upper limit of Voc of the organic photovoltaic cells.
Electrical switching, SET-RESET, and Raman scattering studies on Ge15Te80−xIn5Agx glasses
Authors: Sreevidya Varma G. , Muthu D. V. S. , Sood A. K. , Asokan S.
Published: April 2014

Bulk Ge15Te85−xIn5Agx glasses are shown to exhibit electrical switching with switching/threshold voltages in the range of 70–120 V for a sample thickness of 0.3 mm. Further, the samples exhibit threshold or memory behavior depending on the ON state current. The compositional studies confirm the presence of an intermediate phase in the range 8 ≤ x ≤ 16, revealed earlier by thermal studies. Further, SET-RESET studies have been performed by these glasses using a triangular pulse of 6 mA amplitude (for SET) and 21 mA amplitude (for RESET). Raman studies of the samples after the SET and RESET operations reveal that the SET state is a crystalline phase which is obtained by thermal annealing and the RESET state is the glassy state, similar to the as-quenched samples. It is interesting to note that the samples in the intermediate phase, especially compositions at x = 10, 12, and 14 withstand more set-reset cycles. This indicates compositions in the intermediate phase are better suited for phase change memory applications.
Freezing of sessile water droplets on surfaces with various roughness and wettability
Authors: Hao Pengfei , Lv Cunjing , Zhang Xiwen
Published: April 2014

This paper focus on the freezing delay time and the freezing time of sessile droplet on smooth, micro-structured and micro/nano-structured surfaces, and the whole freezing process are comparatively studied. The freezing delay time of the smooth surfaces with roughness smaller than the size of the critical ice nuclei is found to be much longer than superhydrophobic surfaces with hierarchical structures. Experimental data and theoretical analysis show that the surface roughness plays a very crucial role in nucleation. The freezing delay time could not be extended further on rough surface with more superhydrophobic for sessile droplet. In addition, decreased roughness can increase the free energy barrier for heterogeneous nucleation, result in significant freezing delay. On the contrary, the freezing time from the start of nucleation to the completion of freezing increases with the contact angle. In addition, surfaces with hierarchical roughness are found to have the longest freezing time.
Relation between plasma plume density and gas flow velocity in atmospheric pressure plasma
Authors: Yambe Kiyoyuki , Taka Shogo , Ogura Kazuo
Published: April 2014

We have studied atmospheric pressure plasma generated using a quartz tube, helium gas, and copper foil electrode by applying RF high voltage. The atmospheric pressure plasma in the form of a bullet is released as a plume into the atmosphere. To study the properties of the plasma plume, the plasma plume current is estimated from the difference in currents on the circuit, and the drift velocity is measured using a photodetector. The relation of the plasma plume density nplu, which is estimated from the current and the drift velocity, and the gas flow velocity vgas is examined. It is found that the dependence of the density on the gas flow velocity has relations of nplu ∝ log(vgas). However, the plasma plume density in the laminar flow is higher than that in the turbulent flow. Consequently, in the laminar flow, the density increases with increasing the gas flow velocity.
Charge-trapping characteristics of fluorinated thin ZrO2 film for nonvolatile memory applications
Authors: Huang X. D. , Shi R. P. , Lai P. T.
Published: April 2014

The effects of fluorine treatment on the charge-trapping characteristics of thin ZrO2 film are investigated by physical and electrical characterization techniques. The formation of silicate interlayer at the ZrO2/SiO2 interface is effectively suppressed by fluorine passivation. However, excessive fluorine diffusion into the Si substrate deteriorates the quality of the SiO2/Si interface. Compared with the ZrO2-based memory devices with no or excessive fluorine treatment, the one with suitable fluorine-treatment time shows higher operating speed and better retention due to less resistance of built-in electric field (formed by trapped electrons) against electron injection from the substrate and smaller trap-assisted tunneling leakage, resulting from improved ZrO2/SiO2 and SiO2/Si interfaces.
Time-dependent simulation of prebunched one and two-beam free electron laser
Authors: Mirian N. S. , Maraghechi B.
Published: April 2014

A numerical simulation in one-dimension is conducted to study the slippage effects on prebunched free electron laser. A technique for the simulation of time dependent free electron lasers (FEL) to model the slippage effects is introduced, and the slowly varying envelope approximation in both z and t is used to illustrate the temporal behaviour in the prebunched FEL. Slippage effect on prebunched two-beam FEL is compared with the one-beam modeling. The evaluation of the radiation pulse energy, thermal and phase distribution, and radiation pulse shape in one-beam and two-beam modeling is studied. It was shown that the performance is considerably undermined when the slippage time is comparable to the pulse duration. However, prebunching reduces the slippage. Prebunching also leads to the radiation pulse with a single smooth spike.
Simultaneous enhancement of electron overflow reduction and hole injection promotion by tailoring the last quantum barrier in InGaN/GaN light-emitting diodes
Authors: Kyaw Zabu , Zhang Zi-Hui , Liu Wei , Tiam Tan Swee , Gang Ju Zhen , Liang Zhang Xue , Ji Yun , Hasanov Namig , Zhu Binbin , Lu Shunpeng , Zhang Yiping , Hua Teng Jing , Xiao Wei Sun , Volkan Demir Hilmi
Published: April 2014

A three-step graded undoped-InGaN layers embedded between the GaN last quantum barrier layer and the p-AlGaN electron blocking layer was proposed and its effect on the performance of InGaN/GaN light-emitting diodes was investigated both experimentally and theoretically. In the proposed structure, the electron leakage is found to be effectively reduced, while the hole injection efficiency is simultaneously increased significantly, hence enabling a greatly enhanced radiative recombination rate within the active region. As a result, improvements of 12.25% in the optical output power and 11.98% in the external quantum efficiency are obtained from the proposed device with the respect to the reference device.
Bacterial growth and respiration in laminar flow microbial fuel cells
Authors: Fraiwan Arwa , Call Douglas F. , Choi Seokheun
Published: April 2014

Application of micro-scale microbial fuel cells (MFCs) to power electronics is limited due to the high internal resistances associated with membranes. Laminar flow MFCs (LFMFCs) provide an advantage over conventional designs because the anode and the cathode are naturally separated due to the laminar flow regime that develops within the reactor, eliminating the need for membranes. However, our ability to fully harness the potential of LFMFC technology lags from a lack of in-depth understanding of anode/cathode analyte mixing and fundamental factors that maximize LFMFC's power-generating capabilities. We, therefore, investigated the anode colonization and respiration of the known exoelectrogenic bacterium, Geobacter sulfurreducens, in a micro-scale LFMFC. Current production was dependent on the location of the anode relative to the influent in continuous-flow operation, with the highest current density of 6.5 μA/cm2 recorded closest to the influent. Lateral diffusion of anode/cathode analytes, in addition to upstream substrate consumption, likely resulted in the observed differences in current production. As current increased, the number of bacterial cells on the anode measured using simultaneous microscopic observation, also increased. Although the current density obtained here was substantially lower than other micro-sized MFCs, these findings show that micro-scale LFMFCs adapted to microscopic observation can provide a unique tool for better understanding real-time anode colonization and overall reactor performance.
Numerical study of the influence of applied voltage on the current balance factor of single layer organic light-emitting diodes
Authors: Lu Fei-ping , Liu Xiao-bin , Xing Yong-zhong
Published: April 2014

Current balance factor (CBF) value, the ratio of the recombination current density and the total current density of a device, has an important function in fluorescence-based organic light-emitting diodes (OLEDs), as well as in the performance of the organic electrophosphorescent devices. This paper investigates the influence of the applied voltage of a device on the CBF value of single layer OLED based on the numerical model of a bipolar single layer OLED with organic layer trap free and without doping. Results show that the largest CBF value can be achieved when the electron injection barrier (ϕn) is equal to the hole injection barrier (ϕp) in the lower voltage region at any instance. The largest CBF in the higher voltage region can be achieved in the case of ϕn > ϕp under the condition of electron mobility (μ0n) > hole mobility (μ0p), whereas the result for the case of μ0n < μ0p, is opposite. The largest CBF when μ0n = μ0p can be achieved in the case of ϕn = ϕp in the entire region of the applied voltage. In addition, the CBF value of the device increases with increasing applied voltage. The results obtained in this paper can present an in-depth understanding of the OLED working mechanism and help in the future fabrication of high efficiency OLEDs.
Thermodynamic model of coherent island formation on vicinal substrate
Authors: Zhang Xu , Yu Yanguang , Sun Xiao-Hong , Ren Xiaomin
Published: April 2014

A thermodynamic model has been proposed to address the formation of coherent island on the vicinal substrate. The morphological transition from square based island to elongated based one with various substrate misorientations is described. The initial stage of nucleation and growth process of islands in Stranski–Krastanow system is studied by taking into account the elastic deformations and the change of energy in the case of two-dimensional growth mode. The theoretical analysis shows the minimum nucleation barrier of island is on the decrease with increment of substrate misorientation, which means the nucleation of island on vicinal substrate is more favorable than that on flat substrate. By using the fitting data of experimental results done by Persichetti et al., [Phys. Rev. Lett. 104, 036104 (2010) and Phys. Rev. B 82, 121309(R) (2010)], we provide a meaningful explanation of the experimental observations.
Modified multidimensional scaling approach to analyze financial markets
Authors: Yin Yi , Shang Pengjian
Published: April 2014

Detrended cross-correlation coefficient (σDCCA) and dynamic time warping (DTW) are introduced as the dissimilarity measures, respectively, while multidimensional scaling (MDS) is employed to translate the dissimilarities between daily price returns of 24 stock markets. We first propose MDS based on σDCCA dissimilarity and MDS based on DTW dissimilarity creatively, while MDS based on Euclidean dissimilarity is also employed to provide a reference for comparisons. We apply these methods in order to further visualize the clustering between stock markets. Moreover, we decide to confront MDS with an alternative visualization method, “Unweighed Average” clustering method, for comparison. The MDS analysis and “Unweighed Average” clustering method are employed based on the same dissimilarity. Through the results, we find that MDS gives us a more intuitive mapping for observing stable or emerging clusters of stock markets with similar behavior, while the MDS analysis based on σDCCA dissimilarity can provide more clear, detailed, and accurate information on the classification of the stock markets than the MDS analysis based on Euclidean dissimilarity. The MDS analysis based on DTW dissimilarity indicates more knowledge about the correlations between stock markets particularly and interestingly. Meanwhile, it reflects more abundant results on the clustering of stock markets and is much more intensive than the MDS analysis based on Euclidean dissimilarity. In addition, the graphs, originated from applying MDS methods based on σDCCA dissimilarity and DTW dissimilarity, may also guide the construction of multivariate econometric models.
Accurate modeling of switched reluctance machine based on hybrid trained WNN
Authors: Song Shoujun , Ge Lefei , Ma Shaojie , Zhang Man
Published: April 2014

According to the strong nonlinear electromagnetic characteristics of switched reluctance machine (SRM), a novel accurate modeling method is proposed based on hybrid trained wavelet neural network (WNN) which combines improved genetic algorithm (GA) with gradient descent (GD) method to train the network. In the novel method, WNN is trained by GD method based on the initial weights obtained per improved GA optimization, and the global parallel searching capability of stochastic algorithm and local convergence speed of deterministic algorithm are combined to enhance the training accuracy, stability and speed. Based on the measured electromagnetic characteristics of a 3-phase 12/8-pole SRM, the nonlinear simulation model is built by hybrid trained WNN in Matlab. The phase current and mechanical characteristics from simulation under different working conditions meet well with those from experiments, which indicates the accuracy of the model for dynamic and static performance evaluation of SRM and verifies the effectiveness of the proposed modeling method.
Self-corrected sensors based on atomic absorption spectroscopy for atom flux measurements in molecular beam epitaxy
Authors: Du Y. , Droubay T. C. , Liyu A. V. , Li G. , Chambers S. A.
Published: April 2014

A high sensitivity atom flux sensor based on atomic absorption spectroscopy has been designed and implemented to control electron beam evaporators and effusion cells in a molecular beam epitaxy system. Using a high-resolution spectrometer and a two-dimensional charge coupled device detector in a double-beam configuration, we employ either a non-resonant line or a resonant line with low cross section from the same hollow cathode lamp as the reference for nearly perfect background correction and baseline drift removal. This setup also significantly shortens the warm-up time needed compared to other sensor technologies and drastically reduces the noise coming from the surrounding environment. In addition, the high-resolution spectrometer allows the most sensitive resonant line to be isolated and used to provide excellent signal-to-noise ratio.
Built-in voltage of organic bulk heterojuction p-i-n solar cells measured by electroabsorption spectroscopy
Authors: Siebert-Henze E. , Lyssenko V. G. , Fischer J. , Tietze M. , Brueckner R. , Schwarze M. , Vandewal K. , Ray D. , Riede M. , Leo K.
Published: April 2014

We investigate the influence of the built-in voltage on the performance of organic bulk heterojuction solar cells that are based on a p-i-n structure. Electrical doping in the hole and the electron transport layer allows to tune their work function and hence to adjust the built-in voltage: Changing the doping concentration from 0.5 to 32 wt% induces a shift of the work function towards the transport levels and increases the built-in voltage. To determine the built-in voltage, we use electroabsorption spectroscopy which is based on an evaluation of the spectra caused by a change in absorption due to an electric field (Stark effect). For a model system with a bulk heterojunction of BF-DPB and C60, we show that higher doping concentrations in both the electron and the hole transport layer increase the built-in voltage, leading to an enhanced short circuit current and solar cell performance.
Identifying the Relationship between the Objectively Measured Built Environment and Walking Activity in the High-Density and Transit-Oriented City, Seoul, Korea
Authors: Sung Hyungun , Lee Sugie , Jung Sungwon
Published: April 2014

There has been a great deal of research on the relationship between the built environment and walking activity, but many studies have produced inconclusive or conflicting results. In this research we aim to enrich the association of the built environment with walking activity by examining its impact in Seoul, a Korean megacity characterized by high-density development and a well-equipped public transportation system. The results show that neighborhoods with a relatively higher land-use mix and relatively greater access to public transportation have a significantly positive association with walking activity for destinations that are within a 500 m radius of residences. However, no positive association was found between development density by land use and walking activity. Overall, the results of this study indicate that the relationship between the built environment and walking activity differs by neighborhood scale and the urban built environment in terms of density and public transportation across countries.
Whose integration is this? European forest policy between the gospel of coordination, institutional competition, and a new spirit of integration
Authors: Winkel Georg , Sotirov Metodi
Published: April 2014

Policy integration is a challenging process that involves the renegotiation of interests, beliefs, and sectoral policy boundaries. In this paper we introduce European forest policy as an arena that is characterized by a policy (dis)integration paradox. On the one hand, the need for better coordination and integration of fragmented policies is frequently expressed. On the other hand, little has been achieved in terms of policy integration despite several initiatives. Drawing on fifty semistructured interviews with European forest policy makers and participatory observation, we assess, firstly, effects of and reasons for the disintegration paradox and, secondly, the strategic importance of distinct forest policy initiatives that are legitimized by the need for better policy integration. Our data demonstrate that the forest policy (dis)integration paradox can be explained by different factors, with economic interests and sectoral and institutional competition being most important. Under such circumstances, policy integration serves as frequently used rhetoric to consolidate sectoral interests; however, substance-wise, it is simply not happening.
Assembling the Multitude: Material Geographies of Social Movements from Oaxaca to Occupy
Authors: Arenas Iván
Published: April 2014

In light of the abstract theorizations of scholars of transnational social movement networks—as exemplified by Hardt and Negri's Multitude—in this paper I argue for the power of grounded, material engagements with the practices of protest of social movements to transform not just political spaces, but our theoretical landscapes. I compare the practice of setting up and maintaining encampments in the Oaxaca and Occupy movements to argue that the spatial dynamics of occupation in a tent city fuels the distinctive style of participatory politics of the assembly, providing a creative means to transform confrontation into cooperation. A point of departure for this comparison is my assertion that the political difference made by these social movements lies not just in whether or not they achieved their political goals, but in the kind of intervention that the physical fact of occupying a public space entails in normative understandings of politics and public spaces.