bluuebunny/crossref_metadata_2025 huggingface dataset:
Low secondary electron yield engineered surface for electron cloud mitigation
Authors: Valizadeh Reza , Malyshev Oleg B. , Wang Sihui , Zolotovskaya Svetlana A. , Allan Gillespie W. , Abdolvand Amin
Published: December 2014

Secondary electron yield (SEY or δ) limits the performance of a number of devices. Particularly, in high-energy charged particle accelerators, the beam-induced electron multipacting is one of the main sources of electron cloud (e-cloud) build up on the beam path; in radio frequency wave guides, the electron multipacting limits their lifetime and causes power loss; and in detectors, the secondary electrons define the signal background and reduce the sensitivity. The best solution would be a material with a low SEY coating and for many applications δ < 1 would be sufficient. We report on an alternative surface preparation to the ones that are currently advocated. Three commonly used materials in accelerator vacuum chambers (stainless steel, copper, and aluminium) were laser processed to create a highly regular surface topography. It is shown that this treatment reduces the SEY of the copper, aluminium, and stainless steel from δmax of 1.90, 2.55, and 2.25 to 1.12, 1.45, and 1.12, respectively. The δmax further reduced to 0.76–0.78 for all three treated metals after bombardment with 500 eV electrons to a dose between 3.5 × 10−3 and 2.0 × 10−2 C·mm−2.
Optimization of fuel cell membrane electrode assemblies for transition metal ion-chelating ordered mesoporous carbon cathode catalysts
Authors: Dombrovskis Johanna K. , Prestel Cathrin , Palmqvist Anders E. C.
Published: December 2014

Transition metal ion-chelating ordered mesoporous carbon (TM-OMC) materials were recently shown to be efficient polymer electrolyte membrane fuel cell (PEMFC) catalysts. The structure and properties of these catalysts are largely different from conventional catalyst materials, thus rendering membrane electrode assembly (MEA) preparation parameters developed for conventional catalysts not useful for applications of TM-OMC catalysts. This necessitates development of a methodology to incorporate TM-OMC catalysts in the MEA. Here, an efficient method for MEA preparation using TM-OMC catalyst materials for PEMFC is developed including effects of catalyst/ionomer loading and catalyst/ionomer-mixing and application procedures. An optimized protocol for MEA preparation using TM-OMC catalysts is described.
Dissipation-induced transition of a simple harmonic oscillator
Authors: Shao Zong-Qian , Li Yu-Qi , Pan Xiao-Yin
Published: December 2014

We investigate the dissipation-induced transition probabilities between any two eigenstates of a simple harmonic oscillator. Using the method developed by Yu and Sun [Phys. Rev. A 49, 592 (1994)], the general analytical expressions for the transition probabilities are obtained. The special cases: transition probabilities from the ground state to the first few excited states are then discussed in detail. Different from the previous studies in the literature where only the effect of damping was considered, it is found that the Brownian motion makes the transitions between states of different parity possible. The limitations of the applicability of our results are also discussed.
m-plane (101¯) and (202¯1) GaN/AlxGa1–xN conduction band offsets measured by capacitance-voltage profiling
Authors: Hurni Christophe A. , Kroemer Herbert , Mishra Umesh K. , Speck James S.
Published: December 2014

The reduced polarization of nonpolar and semipolar orientations of the III-Nitrides is very attractive for optoelectronics applications. Several properties of these orientations have yet to be investigated. In particular, there is no a priori reason for the band offset to be the same for different crystallographical orientations. In the present article, we report on the extraction of the GaN/AlxGa1–xN conduction band offsets through capacitance-voltage profiling for m-plane (101¯0) and (202¯1) orientations. We extracted a ΔEc:ΔEv of 50:50–60:40. We measured a non-zero hetero-interface charge for the (202¯1) orientation which made the extraction of ΔEc less reliable.
Comparative modelling of chemical ordering in palladium-iridium nanoalloys
Authors: Davis Jack B. A. , Johnston Roy L. , Rubinovich Leonid , Polak Micha
Published: December 2014

Chemical ordering in “magic-number” palladium-iridium nanoalloys has been studied by means of density functional theory (DFT) computations, and compared to those obtained by the Free Energy Concentration Expansion Method (FCEM) using derived coordination dependent bond energy variations (CBEV), and by the Birmingham Cluster Genetic Algorithm using the Gupta potential. Several compositions have been studied for 38- and 79-atom particles as well as the site preference for a single Ir dopant atom in the 201-atom truncated octahedron (TO). The 79- and 38-atom nanoalloy homotops predicted for the TO by the FCEM/CBEV are shown to be, respectively, the global minima and competitive low energy minima. Significant reordering of minima predicted by the Gupta potential is seen after reoptimisation at the DFT level.
Partitioning and structural role of Mn and Fe ions in ionic sulfophosphate glasses
Authors: Möncke Doris , Sirotkin Sergey , Stavrou Elissaios , Kamitsos Efstratios I. , Wondraczek Lothar
Published: December 2014

Ionic sulfophosphate liquids of the type ZnO-Na2O-Na2SO4-P2O5 exhibit surprising glass forming ability, even at slow or moderate cooling rate. As a concept, they also provide high solubility of transition metal ions which could act as cross-linking sites between the sulfate and phosphate entities. It is therefore investigated how the replacement of ZnO by MnO and/or FeO affects the glass structure and the glass properties. Increasing manganese levels are found to result in a monotonic increase of the transition temperature Tg and most of the mechanical properties. This trend is attributed to the change of metal-ion coordination from four-fold around Zn2+ to six-fold around Mn2+ ions. The higher coordination facilitates cross-linking of the ionic structural entities and subsequently increases Tg. Raman and infrared spectroscopy show that the structure of these glasses involves only SO42− and PO43− monomers as well as P2O74- dimers. Replacement of ZnO by MnO is found to favour PO43− over P2O74- species, a trend which is enhanced by co-doping with FeO. Both transition metal ions show, like Zn2+, a preference to selectively coordinate to phosphate anionic species, as opposed to sodium ions which coordinate mainly to sulfate anions. EPR spectroscopy finally shows that divalent Mn2+ ions are present primarily in MnO6-clusters, which, in the studied sulfophosphate glasses, convert upon increasing MnO content from corner-sharing to edge-sharing entities.
An algorithm for selecting the most accurate protocol for contact angle measurement by drop shape analysis
Authors: Xu Z. N.
Published: December 2014

In this study, an error analysis is performed to study real water drop images and the corresponding numerically generated water drop profiles for three widely used static contact angle algorithms: the circle- and ellipse-fitting algorithms and the axisymmetric drop shape analysis-profile (ADSA-P) algorithm. The results demonstrate the accuracy of the numerically generated drop profiles based on the Laplace equation. A significant number of water drop profiles with different volumes, contact angles, and noise levels are generated, and the influences of the three factors on the accuracies of the three algorithms are systematically investigated. The results reveal that the above-mentioned three algorithms are complementary. In fact, the circle- and ellipse-fitting algorithms show low errors and are highly resistant to noise for water drops with small/medium volumes and contact angles, while for water drop with large volumes and contact angles just the ADSA-P algorithm can meet accuracy requirement. However, this algorithm introduces significant errors in the case of small volumes and contact angles because of its high sensitivity to noise. The critical water drop volumes of the circle- and ellipse-fitting algorithms corresponding to a certain contact angle error are obtained through a significant amount of computation. To improve the precision of the static contact angle measurement, a more accurate algorithm based on a combination of the three algorithms is proposed. Following a systematic investigation, the algorithm selection rule is described in detail, while maintaining the advantages of the three algorithms and overcoming their deficiencies. In general, static contact angles over the entire hydrophobicity range can be accurately evaluated using the proposed algorithm. The ease of erroneous judgment in static contact angle measurements is avoided. The proposed algorithm is validated by a static contact angle evaluation of real and numerically generated water drop images with different hydrophobicity values and volumes.
Pf1 bacteriophage hydration by magic angle spinning solid-state NMR
Authors: Sergeyev Ivan V. , Bahri Salima , Day Loren A. , McDermott Ann E.
Published: December 2014

High resolution two- and three-dimensional heteronuclear correlation spectroscopy (1H–13C, 1H–15N, and 1H–13C–13C HETCOR) has provided a detailed characterization of the internal and external hydration water of the Pf1 virion. This long and slender virion (2000 nm × 7 nm) contains highly stretched DNA within a capsid of small protein subunits, each only 46 amino acid residues. HETCOR cross-peaks have been unambiguously assigned to 25 amino acids, including most external residues 1–21 as well as residues 39–40 and 43–46 deep inside the virion. In addition, the deoxyribose rings of the DNA near the virion axis are in contact with water. The sets of cross-peaks to the DNA and to all 25 amino acid residues were from the same hydration water 1H resonance; some of the assigned residues do not have exchangeable side-chain protons. A mapping of the contacts onto structural models indicates the presence of water “tunnels” through a highly hydrophobic region of the capsid. The present results significantly extend and modify results from a lower resolution study, and yield a comprehensive hydration surface map of Pf1. In addition, the internal water could be distinguished from external hydration water by means of paramagnetic relaxation enhancement. The internal water population may serve as a conveniently localized magnetization reservoir for structural studies.
THz absorption spectroscopy of solvated β-lactoglobulin
Authors: Vondracek Hendrik , Dielmann-Gessner Jessica , Lubitz Wolfgang , Knipp Markus , Havenith Martina
Published: December 2014

The influence of β-lactoglobulin (βLG) on the fast sub-picosecond collective hydration dynamics in the solvent was investigated by THz absorption spectroscopy as a function of pH. It is well-known that a change in pH from pH 6 to pH 8 reversibly opens or closes the binding cavity by a transition of the E-F loop. Furthermore, the aggregation of the protein into dimers is affected, which is thought to be triggered by changes in the enzyme's electrostatic potential. Our data reveal that pH has a clear influence on the THz absorption of βLG. We discuss this influence in light of the changes observed in the sub-psec solute/solvent dynamics when probed by THz spectroscopy, which are, in turn, seen to correlate with changes in the pH value.
Adaptive cluster expansion approach for predicting the structure evolution of graphene oxide
Authors: Li Xi-Bo , Guo Pan , Wang D. , Zhang Yongsheng , Liu Li-Min
Published: December 2014

An adaptive cluster expansion (CE) method is used to explore surface adsorption and growth processes. Unlike the traditional CE method, suitable effective cluster interaction (ECI) parameters are determined, and then the selected fixed number of ECIs is continually optimized to predict the stable configurations with gradual increase of adatom coverage. Comparing with traditional CE method, the efficiency of the adaptive CE method could be greatly enhanced. As an application, the adsorption and growth of oxygen atoms on one side of pristine graphene was carefully investigated using this method in combination with first-principles calculations. The calculated results successfully uncover the structural evolution of graphene oxide for the different numbers of oxygen adatoms on graphene. The aggregation behavior of the stable configurations for different oxygen adatom coverages is revealed for increasing coverages of oxygen atoms. As a targeted method, adaptive CE can also be applied to understand the evolution of other surface adsorption and growth processes.
Understanding generalized inversions of nuclear magnetic resonance transverse relaxation time in porous media
Authors: Mitchell J. , Chandrasekera T. C.
Published: December 2014

The nuclear magnetic resonance transverse relaxation time T2, measured using the Carr-Purcell-Meiboom-Gill (CPMG) experiment, is a powerful method for obtaining unique information on liquids confined in porous media. Furthermore, T2 provides structural information on the porous material itself and has many applications in petrophysics, biophysics, and chemical engineering. Robust interpretation of T2 distributions demands appropriate processing of the measured data since T2 is influenced by diffusion through magnetic field inhomogeneities occurring at the pore scale, caused by the liquid/solid susceptibility contrast. Previously, we introduced a generic model for the diffusion exponent of the form \documentclass[12pt]{minimal}\begin{document}$-ant_{\rm e}^k$\end{document}−antek (where n is the number and te the temporal separation of spin echoes, and a is a composite diffusion parameter) in order to distinguish the influence of relaxation and diffusion in CPMG data. Here, we improve the analysis by introducing an automatic search for the optimum power k that best describes the diffusion behavior. This automated method is more efficient than the manual trial-and-error grid search adopted previously, and avoids variability through subjective judgments of experimentalists. Although our method does not avoid the inherent assumption that the diffusion exponent depends on a single k value, we show through simulation and experiment that it is robust in measurements of heterogeneous systems that violate this assumption. In this way, we obtain quantitative T2 distributions from complicated porous structures and demonstrate the analysis with examples of ceramics used for filtration and catalysis, and limestone of relevance to the construction and petroleum industries.
Suppression of the molecular ultra-fast dissociation in bromomethane clusters
Authors: Rander T. , Lindblad A. , Bradeanu I. , Öhrwall G. , Svensson S. , Björneholm O.
Published: December 2014

We address the influence of clustering on the ultra-fast dissociation of bromomethane. Valence and core photo-electron spectroscopy, partial electron yield absorption, and resonant Auger spectroscopy have been used together with ab initio calculations to investigate the properties of the ultra-fast dissociation. The ratio of ultra-fast dissociation of molecules in clusters as compared to free molecules is determined to be significantly reduced. We propose partial delocalization of the excited electronic state as being responsible for this behavior.
Note: High precision measurements using high frequency gigahertz signals
Authors: Jin Aohan , Fu Siyuan , Sakurai Atsunori , Liu Liang , Edman Fredrik , Pullerits Tõnu , Öwall Viktor , Karki Khadga Jung
Published: December 2014

Generalized lock-in amplifiers use digital cavities with Q-factors as high as 5 × 108 to measure signals with very high precision. In this Note, we show that generalized lock-in amplifiers can be used to analyze microwave (giga-hertz) signals with a precision of few tens of hertz. We propose that the physical changes in the medium of propagation can be measured precisely by the ultra-high precision measurement of the signal. We provide evidence to our proposition by verifying the Newton's law of cooling by measuring the effect of change in temperature on the phase and amplitude of the signals propagating through two calibrated cables. The technique could be used to precisely measure different physical properties of the propagation medium, for example, the change in length, resistance, etc. Real time implementation of the technique can open up new methodologies of in situ virtual metrology in material design.
Terahertz photodetectors based on tapered semiconductor nanowires
Authors: Romeo L. , Coquillat D. , Husanu E. , Ercolani D. , Tredicucci A. , Beltram F. , Sorba L. , Knap W. , Vitiello M. S.
Published: December 2014

We report on the demonstration of Terahertz (THz) broadband detectors based on field effect transistors exploiting tapered semiconductor nanowires. The intrinsic asymmetry provided by the nanowires geometry allows to achieve responsivity values as high as 55 V/W (2.5 mA/W) and a noise-equivalent-power of 3 × 10−10 W/Hz1/2 independent of the specific gate voltage applied. The possibility to reduce the number of terminals required to the source and drain contacts only and the technological feasibility of multi-pixel arrays are promising for the realization of compact and integrated THz matrix array detection systems.
Effect of multipole excitations in electron energy-loss spectroscopy of surface plasmon modes in silver nanowires
Authors: Zhou Xiuli , Hörl Anton , Trügler Andreas , Hohenester Ulrich , Norris Theodore B. , Herzing Andrew A.
Published: December 2014

We have characterized the surface plasmon resonance (SPR) in silver nanowires using spatially resolved electron energy loss spectroscopy (EELS) in the scanning transmission electron microscope. Non-symmetric EELS spectra due to high-k SPR propagation along the nanowire and spectral shifts due to higher-order mode excitation are observed when the beam is positioned near the tip of the nanowire. When the beam is far from the tip region and on the side of nanowire, no spectral shifts are observed as the beam is scanned in the radial direction of the nanowire. The experimental spectra are compared with three different theoretical approaches: direct numerical calculation of the energy loss, analytical models for energy loss, and numerical simulations using an optical model. All three models reproduce the spectral shifts as the electron beam approaches the cap of the nanowire. The analytical model reveals the origin of the shifts in high-order plasmon mode excitation.
Long-range orientation correlation in water
Authors: Shelton David P.
Published: December 2014

Strong short-range intermolecular interactions result in position and orientation correlations between nearest neighbour molecules in isotropic liquids, but it is generally assumed that such correlations extend at most a few molecular diameters. Results from second-harmonic light scattering experiments presented here reveal long-range molecular orientation correlations in liquid water, where the molecular dipole orientation distribution has the form of a nearly pure transverse vector field. Spatial scales in the range 200–2000 nm are probed by the angle-dependent measurements and the observed correlations are thought to result from rotation-translation coupling in acoustic phonons in the liquid.
Thermal behavior in Se-Te chalcogenide system: Interplay of thermodynamics and kinetics
Authors: Svoboda Roman , Málek Jiří
Published: December 2014

Heat capacity measurements were performed for Se, Se90Te10, Se80Te20, and Se70Te30 materials in the 230–630 K temperature range. Both glassy and crystalline Cp dependences were found to be identical within the experimental error. The compositional dependence of the N-type undercooled liquid Cp evolution was explained on the basis of free-volume theory; vibrational and chemical contributions to heat capacity were found to be roughly similar for all Se-Te compositions. The thermal behavior in the Se-Te chalcogenide system was thoroughly studied: glass transition, cold crystallization, and melting were investigated in dependence on composition and various experimental conditions (heating rate, particle size, and pre-nucleation period). The kinetics of the structural relaxation and crystallization processes are described in terms of the Tool-Narayanaswamy-Moynihan and Johnson-Mehl-Avrami models. The complexity of these processes is thoroughly discussed with regard to the compositionally determined changes of molecular structures. The discussion is conducted in terms of the mutual interplay between the thermodynamics and kinetics in this system.
A new formulation for surface roughness limited mobility in bulk and ultra-thin-body metal–oxide–semiconductor transistors
Authors: Lizzit Daniel , Esseni David , Palestri Pierpaolo , Selmi Luca
Published: December 2014

This paper presents a new model for the surface roughness (SR) limited mobility in MOS transistors. The model is suitable for bulk and thin body devices and explicitly takes into account the non linear relation between the displacement Δ of the interface position and the SR scattering matrix elements, which is found to significantly influence the r.m.s value (Δrms) of the interface roughness that is necessary to reproduce SR-limited mobility measurements. In particular, comparison with experimental mobility for bulk Si MOSFETs shows that with the new SR scattering model a good agreement with measured mobility can be obtained with Δrms values of about 0.2 nm, which is in good agreement with several AFM and TEM measurements. For thin body III–V MOSFETs, the proposed model predicts a weaker mobility degradation at small well thicknesses (Tw), compared to the Tw6 behavior observed in Si extremely thin body devices.
Large improvement of phosphorus incorporation efficiency in n-type chemical vapor deposition of diamond
Authors: Ohtani Ryota , Yamamoto Takashi , Janssens Stoffel D. , Yamasaki Satoshi , Koizumi Satoshi
Published: December 2014

Microwave plasma enhanced chemical vapor deposition is a promising way to generate n-type, e.g., phosphorus-doped, diamond layers for the fabrication of electronic components, which can operate at extreme conditions. However, a deeper understanding of the doping process is lacking and low phosphorus incorporation efficiencies are generally observed. In this work, it is shown that systematically changing the internal design of a non-commercial chemical vapor deposition chamber, used to grow diamond layers, leads to a large increase of the phosphorus doping efficiency in diamond, produced in this device, without compromising its electronic properties. Compared to the initial reactor design, the doping efficiency is about 100 times higher, reaching 10%, and for a very broad doping range, the doping efficiency remains highly constant. It is hypothesized that redesigning the deposition chamber generates a higher flow of active phosphorus species towards the substrate, thereby increasing phosphorus incorporation in diamond and reducing deposition of phosphorus species at reactor walls, which additionally reduces undesirable memory effects.
A two degrees-of-freedom piezoelectric single-crystal micromotor
Authors: Chen Zhijiang , Li Xiaotian , Liu Guoxi , Dong Shuxiang
Published: December 2014

A two degrees-of-freedom (DOF) ultrasonic micromotor made of piezoelectric Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIN-PMN-PT) single crystal square-bar (dimensions 2 × 2 × 9 mm3) was developed. The PIN-PMN-PT square-bar stator can generate standing wave elliptical motions in two orthogonal vertical planes by combining the first longitudinal and second bending vibration modes, enabling it to drive a slider in two orthogonal directions. The relatively large driving forces of 0.25 N and motion speed of 35 mm/s were obtained under a voltage of 80 Vpp at its resonance frequency of 87.5 kHz. The proposed micromotor has potential for applications in micro robots, cell manipulators, and digital cameras as a two-DOF actuator.
Analysis of the alternating current conductivity and magnetic behaviors for the polycrystalline Y-type Ba0.5Sr1.5Co2(Fe1-xAlx)12O22 hexaferrites
Authors: Wu M. X. , Zhong W. J. , Gao X. S. , Liu L. J. , Liu Z. W.
Published: December 2014

Co2Y hexaferrites have attracted intensive interests due to its potential high temperature magnetoelectricity as the single phase multiferroics. Numerous efforts have been paid to enhance their magnetoelectric properties at high temperatures through increasing the magnetic transition temperature and decreasing the conductivity. In this work, we investigated the conductivity and magnetic properties of the polycrystalline Ba0.5Sr1.5Co2(Fe1−xAlx)12O22 (0 ≤ x ≤ 0.12) hexaferrites and found that Al-doping has important effects on both the conductivity and magnetic properties. The underlying physical mechanisms were also systematically analyzed. Most importantly, a very much enhanced resistivity (over 10 MΩ cm), and a high magnetic transition temperature (∼346 K) have been obtained at a doping amount of x = 0.04. These improvements are very promising for achieving significant magnetoelectric effect at room temperature. The current research can provide the basic understanding of the Y-type ferrites for future applications in magnetoelectric and other fields.
Humidity induced charge migration on single layer graphene oxide sheets
Authors: Wang Ying , Shen Yue , Zhang Xueqiang , Zhang Yi , Hu Jun
Published: December 2014

The charge migration on the surface of single layer graphene oxide (GO) sheets was investigated by scanning polarization force microscopy. Electrostatic charges were observed to transfer over 1 μm across the insulating single layer GO sheets surface with the help of water molecules condensed from the environment. Humidity-dependent charge migration on GO sheets was visualized on the nanometer scale and the migration velocity was plotted at a relative humidity range of 10%–40%. When the relative humidity reached 50% or higher, water film would form on the whole GO sheet surface, which made the GO sheet conductive to the electrostatic charges.
Constructive polarization modulation for coherent population trapping clock
Authors: Yun Peter , Danet Jean-Marie , Holleville David , de Clercq Emeric , Guérandel Stéphane
Published: December 2014

We propose a constructive polarization modulation scheme for atomic clocks based on coherent population trapping (CPT). In this scheme, the polarization of a bichromatic laser beam is modulated between two opposite circular polarizations to avoid trapping the atomic populations in the extreme Zeeman sublevels. We show that if an appropriate phase modulation between the two optical components of the bichromatic laser is applied synchronously, the two CPT dark states which are produced successively by the alternate polarizations add constructively. Measured CPT resonance contrasts up to 20% in one-pulse CPT and 12% in two-pulse Ramsey-CPT experiments are reported, demonstrating the potential of this scheme for applications to high performance atomic clocks.
Hybrid whispering gallery mode/plasmonic chain ring resonators for biosensing
Authors: Arbabi Ehsan , Kamali Seyedeh Mahsa , Arnold Stephen , Goddard Lynford L.
Published: December 2014

We analyze the physics of hybrid whispering gallery mode resonators formed by arranging a periodic array of epitopes (i.e., gold nano-shells covering silica nano-spheres) around the equator of a silica microsphere. When the epitopes are located at the antinodes of the field of the whispering gallery mode, we find that the field localization properties near the epitopes change drastically as the radius of the epitopes is varied due to the existence of distinct coupling regions of the hybrid resonator. We investigated the application of such resonators for biosensing by calculating the resonance wavelength shift caused by a binding event of a single Thyroglobulin cancer marker protein to the surface of an epitope in the chain.
Development of flow through dielectrophoresis microfluidic chips for biofuel production: Sorting and detection of microalgae with different lipid contents
Authors: Deng Yu-Luen , Kuo Mei-Yi , Juang Yi-Je
Published: December 2014

In this study, a continuous flow dielectrophoresis (DEP) microfluidic chip was fabricated and utilized to sort out the microalgae (C. vulgaris) with different lipid contents. The proposed separation scheme is to allow that the microalgae with different lipid contents experience different negative or no DEP force at the separation electrode pair under the pressure-driven flow. The microalgae that experience stronger negative DEP will be directed to the side channel while those experience less negative or no DEP force will pass through the separation electrode pair to remain in the main channel. It was found that the higher the lipid content inside the microalgae, the higher the crossover frequency. Separation of the microalgae with 13% and 21% lipid contents, and 24% and 30%–35% lipid contents was achieved at the operating frequency 7 MHz, and 10 MHz, respectively. Moreover, separation can be further verified by measurement of the fluorescence intensity of the neutral lipid inside the sorted algal cells.
Temperature-dependent carrier–phonon coupling in topological insulator Bi2Se3
Authors: Lai Yi-Ping , Chen Hsueh-Ju , Wu Kuang-Hsiung , Liu Jia-Ming
Published: December 2014

Temperature-dependent (11.0 K−294.5 K) carrier–phonon coupling in Bi2Se3 is investigated by ultrafast pump−probe spectroscopy. The rise time of the differential reflectivity is interpreted by a combined effect of electron temperature relaxation and hot-phonon lifetime. The electron−phonon coupling constant of the bulk state (λ=0.63±0.05) is deduced from theoretical fitting. Increasing hot-phonon lifetime with decreasing temperature is attributed to a decreasing phonon−phonon collision rate. A complete analysis of the thermalization process is presented. Understanding carrier and phonon dynamics is essential for future optoelectronic and spintronic applications of topological insulators.
High electrostrictive coefficient Q33 in lead-free Ba(Zr0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3 piezoelectric ceramics
Authors: Li Fei , Jin Li , Guo Runping
Published: December 2014

In this study, the electrostrictive effect in Ba(Zr0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3 (BZT-xBCT, x = 0.4, 0.5, and 0.6) ceramics was investigated to gain understanding of their high piezoelectric activity. The electrostrictive coefficient Q33 of the BZT-xBCT ceramics was observed to be around 0.04 m4/C2, twice that reported for Pb(Zr,Ti)O3-based ceramics. The Q33 was found to be quite stable with respect to temperature and composition for the BZT-xBCT ceramics. The addition of Fe3+ dopant to the ceramics greatly decreased their Curie temperature without affecting their Q33, which remained 0.04 m4/C2. Moreover, a high and hysteresis-free electric-field-induced strain was obtained for 2 at. % Fe-doped BZT-0.5BCT ceramics at room temperature, caused by their high Q33 coefficient and lower-than-room-temperature Curie temperature. The small-signal M33 coefficient of 2 at. % Fe-doped BZT-0.5BCT ceramics was found to be 1.5 × 10−16 m2/V2 (0.32 × 10−16 m2/V2 for undoped counterpart). These results indicate that 2 at. % Fe-doped BZT-0.5BCT ceramics have great potential as alternatives for hard Pb(Zr,Ti)O3 ceramics in actuator applications, where reproducible and non-hysteretic deformation responses are required.
Absorption features of the zero frequency mode in an ultra-thin slab
Authors: Llorens Jose M. , Buencuerpo Jerónimo , Postigo Pablo Aitor
Published: December 2014

The optical absorption in a homogeneous and non-dispersive slab is governed by the well-known Fabry-Perot resonances. We have found that below the lowest order Fabry-Perot resonance, there is another absorption maximum due to the zero frequency mode whose peak frequency is given not by the real part of the complex resonance frequency, as it is the case for all other resonances, but by the imaginary part. This result is of interest, among other applications, for ultra thin solar cells, as tuning the zero frequency mode peak with the maximum of solar irradiance results in an increased efficiency.
Effects of hydrogen atoms on surface conductivity of diamond film
Authors: Liu Fengbin , Cui Yan , Qu Min , Di Jiejian
Published: December 2014

To investigate the effects of surface chemisorbed hydrogen atoms and hydrogen atoms in the subsurface region of diamond on surface conductivity, models of hydrogen atoms chemisorbed on diamond with (100) orientation and various concentrations of hydrogen atoms in the subsurface layer of the diamond were built. By using the first-principles method based on density functional theory, the equilibrium geometries and densities of states of the models were studied. The results showed that the surface chemisorbed hydrogen alone could not induce high surface conductivity. In addition, isolated hydrogen atoms in the subsurface layer of the diamond prefer to exist at the bond centre site of the C-C bond. However, such a structure would induce deep localized states, which could not improve the surface conductivity. When the hydrogen concentration increases, the C-H-C-H structure and C-3Hbc-C structure in the subsurface region are more stable than other configurations. The former is not beneficial to the increase of the surface conductivity. However, the latter would induce strong surface states near the Fermi level, which would give rise to high surface conductivity. Thus, a high concentration of subsurface hydrogen atoms in diamond would make significant contributions to surface conductivity.
Neoliberalism, Big Society, and Progressive Localism
Authors: Williams Andrew , Goodwin Mark , Cloke Paul
Published: December 2014

In the UK the current Coalition government has introduced an unprecedented set of reforms to welfare, public services, and local governance under the rubric of ‘localism’. Conventional analytics of neoliberalism have commonly portrayed the impacts of these changes in the architectures of governance in blanket terms: as an utterly regressive dilution of local democracy; as an extension of conservative political technology by which state welfare is denuded in favour of market-led individualism; and as a further politicised subjectification of the charitable self. Such seemingly hegemonic grammars of critique can ignore or underestimate the progressive possibilities for creating new ethical and political spaces in amongst the neoliberal canvas. In this paper we investigate the localism agenda using alternative interpretative grammars that are more open to the recognition of interstitial politics of resistance and experimentation that are springing up within, across, and beyond formations of the neoliberal. We analyse the broad framework of intentional localisms laid down by the Coalition government, and then point to four significant pathways by which more progressive articulations of localism have been emerging in amongst the neoliberal infrastructure. In so doing we seek to endorse and expand imaginations of political activism that accentuate an interstitial political sensibility that works strategically, and even subversively, with the tools at hand.
Cross-Sectoral Influence, Planning Policy, and Industrial Property Market in a High-Density City: A Hong Kong Study 1978–2012
Authors: Tang Bo-Sin , Ho Winky K O
Published: December 2014

Why did Hong Kong property developers continue to produce a large amount of new industrial accommodation despite the city exhibiting a strong trend of deindustrialization since the late 1970s? This study addresses this question by examining a longitudinal cross-sectoral interaction between industrial and office property markets and its relationship with planning policy. It theorizes about the substitutability between industrial and office accommodation and hypothesizes that the use of new industrial premises by nonmanufacturing operators may be the answer. Using the methodology of Johansen cointegration and a vector error correction model, our estimations have found that industrial rent, price, and supply were influenced by both changing economic structure and office market parameters. Cross-sectoral influences between industrial and office property markets were confirmed.
Badger Vaccination: Dimensions of Trust and Confidence in the Governance of Animal Disease
Authors: Enticott Gareth , Maye Damian , Fisher Rhiannon , Ilbery Brian , Kirwan James
Published: December 2014

This paper examines farmers' trust in badger vaccination as a method of preventing the spread of bovine tuberculosis (bTB) between wildlife (specifically, badgers) and cattle in England. The spread of bTB has economic and social implications for farmers, but previous research has found that lack of trust in government is a key factor in farmers' failure to adopt new preventative biosecurity practices. In these and other studies, however, the conceptual dimensions of trust are frequently loosely defined, meaning that it is unclear how trust, along with other factors, is related to the acceptance of new biosecurity practices such as vaccination. Drawing on findings from a telephone survey of 339 farmers and in-depth interviews with a subsample of 65, the paper explores attitudes towards, and levels of acceptance of, badger vaccination amongst farmers across five study areas with varying levels of bTB disease. Results reveal low levels both of trust in government to manage bTB and confidence in badger vaccination. Principal components analysis identifies three specific dimensions of trust which, along with farmers' perceived self-efficacy, the perceived threat of disease, and faith in others to manage disease, are all significantly related to the acceptability of badger vaccination.
Vehicle Miles Traveled and the Built Environment: Evidence from Vehicle Safety Inspection Data
Authors: Diao M i , Ferreira Joseph
Published: December 2014

This study examines the linkage between household vehicle usage and their residential locations within a metropolitan area using a newly available administrative dataset of annual private passenger vehicle safety inspection records (with odometer readings) and spatially detailed data on the built environment. Vehicle miles travelled (VMT) and a set of comprehensive built-environment measures are computed for a statewide 250 × 250 m grid cell layer using advanced geographic information systems and database management tools. We apply factor analysis to construct five factors that differentiate the built-environment characteristics of the grid cells and then integrate the built-environment factors into spatial regression models of household vehicle usage that account for built environment, demographics, and spatial interactions. The empirical results suggest that built-environment factors not only play an important role in explaining the intraurban variation of household vehicle usage, but may also be underestimated by previous studies that use more aggregate built-environment measures. One-standard-deviation variations in the built-environment factors are associated with as much as 5000-mile differences in annual VMT per household. This study also demonstrates the potential value of new georeferenced administrative datasets in developing indicators that can assist urban planning and urban management.
‘A Country on Wheels’: A Mobile Ethnography of Portuguese Lorry Drivers
Authors: Nóvoa André
Published: December 2014

This paper revolves around the intersections of mobility and identity. In Europe mobility is often regarded as a producer of cultural proximity amongst European citizens and member states, bearing the potential to fabricate some kind of European identity. Many of the top-down policies of the European Union have been based on the assumption that the more we move, the more European we become. In this paper my intention is to contribute to this debate, bringing to the foreground a case of mobility in Europe that contradicts this vision: the mobile lives of Portuguese truck drivers, from a particular Portuguese company, within the Eurozone. Through an ethnographic account of these individuals, I show how mobility can be responsible for a reproduction of strong local identities. Rather than culturally transposing barriers, the drivers live their professional lives in a kind of nationalised nutshell on wheels. These findings present an opportunity to reflect on how the European free market requires a form of immobilised movement from many professionals in order to function smoothly. In fact, the freedom of many (European citizens) may entail the confinement of others.
Forced Mobility: The Relocation of Public-Housing Residents in Atlanta
Authors: Hankins Katherine , Puckett Mechelle , Oakley Deirdre , Ruel Erin
Published: December 2014

In this paper we argue for the use of ‘mobility’ to describe not just bodily movement, travel, or transport, but as a concept that animates the constellation of policies and power relations that simultaneously move and spatially fix the urban poor. Using a framework developed by Creswell in 2010, in which mobility operates as ‘an entanglement of movement, representation, and practice’, this paper examines the mobility of relocated public-housing residents, who are forced to move as a result of the demolition of project-based housing in the city of Atlanta. It draws from Cresswell's conceptualization of the politics of mobility in terms of motive force, speed, rhythm, route, experience, and friction to more fully understand the mobilities and immobilities of the urban poor as they respond to the neoliberalization of housing policy in cities like Atlanta. Based on our study, we propose the addition of ‘resources’ to Cresswell's framework to more fully capture the importance of individuals' abilities to navigate the complexities of residential relocation, as they draw on a variety of social networks, skills, and faith dispositions. Through a qualitative analysis of interviews and the voice and photographic journals of relocated public-housing residents as they recorded their eviction and relocation process, this paper documents their circulation processes against the backdrop of the city's neoliberalizing housing policies.
Children, Urban Care, and Everyday Pavements
Authors: Kullman Kim
Published: December 2014

This paper takes a mundane piece of urban infrastructure, the pavement, as a starting point, approaching it through the experiences of 7–12-year-old children who journey between home and school in Helsinki, Finland. In doing so, the paper argues that the children and their travel companions are employing pavements to cultivate the caring potential of their city, whether this entails patting dogs, picking up empty bottles, or checking the safety of zebra crossings. Inspired by recent work on the geographies of care and affect attunement, the paper develops the notion of urban care to explore the implications of these child–pavement entanglements for the wider good of cities. Children are commonly understood as passive recipients of adult care in mundane spaces, but the paper demonstrates that children are actually skilled urban carers who maintain a range of attachments not only to their friends, siblings, and parents but also to various human and nonhuman strangers participating in the collective life of cities. The notion of urban care invites recognition of this relational work, engaging as it does with questions concerning the ways in which citizens might best attend to their fragile environments.
Analogs of natural aminoacyl-tRNA synthetase inhibitors clear malaria in vivo
Authors: Novoa Eva Maria , Camacho Noelia , Tor Anna , Wilkinson Barrie , Moss Steven , Marín-García Patricia , Azcárate Isabel G. , Bautista José M. , Mirando Adam C. , Francklyn Christopher S. , Varon Sònia , Royo Miriam , Cortés Alfred , Ribas de Pouplana Lluís
Published: December 2014

Significance

Malaria remains one of the main health threats in the developing world, with staggering social and economic costs. Resistance to artemisins, the main pharmacological tool currently available against malaria, has been widely reported. Borrelidin, a natural compound that inhibits threonyl-tRNA synthetase, has long been studied for its antibacterial and antiparasitic properties, but undesirable toxic effects prevented its further clinical development. Here we present a group of borrelidin derivatives that retain their ability to inhibit
Plasmodium
threonyl-tRNA synthetase but not its human homolog. Furthermore, we demonstrate, for the first time to our knowledge, that these compounds are capable of effectively clearing a
Plasmodium
infection in animals, curing malaria with a potency equivalent to reference drugs such as chloroquine.
Microbiota organization is a distinct feature of proximal colorectal cancers
Authors: Dejea Christine M. , Wick Elizabeth C. , Hechenbleikner Elizabeth M. , White James R. , Mark Welch Jessica L. , Rossetti Blair J. , Peterson Scott N. , Snesrud Erik C. , Borisy Gary G. , Lazarev Mark , Stein Ellen , Vadivelu Jamuna , Roslani April C. , Malik Ausuma A. , Wanyiri Jane W. , Goh Khean L. , Thevambiga Iyadorai , Fu Kai , Wan Fengyi , Llosa Nicolas , Housseau Franck , Romans Katharine , Wu XinQun , McAllister Florencia M. , Wu Shaoguang , Vogelstein Bert , Kinzler Kenneth W. , Pardoll Drew M. , Sears Cynthia L.
Published: December 2014

Significance

We demonstrate, to our knowledge for the first time, that bacterial biofilms are associated with colorectal cancers, one of the leading malignancies in the United States and abroad. Colon biofilms, dense communities of bacteria encased in a likely complex matrix that contact the colon epithelial cells, are nearly universal on right colon tumors. Most remarkably, biofilm presence correlates with bacterial tissue invasion and changes in tissue biology with enhanced cellular proliferation, a basic feature of oncogenic transformation occurring even in colons without evidence of cancer. Microbiome profiling revealed that biofilm communities on paired normal mucosa cluster with tumor microbiomes but lack distinct taxa differences. This work introduces a previously unidentified concept whereby microbial community structural organization exhibits the potential to contribute to disease progression.
Direct measurements of methane emissions from abandoned oil and gas wells in Pennsylvania
Authors: Kang Mary , Kanno Cynthia M. , Reid Matthew C. , Zhang Xin , Mauzerall Denise L. , Celia Michael A. , Chen Yuheng , Onstott Tullis C.
Published: December 2014

Significance

Recent studies indicate that greenhouse gas emission inventories are likely missing methane emission sources. We conducted the first methane emission measurements from abandoned oil and gas wells and found substantial emissions, particularly from high-emitting abandoned wells. These emissions are not currently considered in any emissions inventory. We scaled methane emissions from our direct measurements of abandoned wells in Pennsylvania and calculate that they represent 4–7% of current total anthropogenic methane emissions in Pennsylvania. Millions of abandoned wells exist across the country and some are likely to be high emitters. Additional measurements of methane emissions from abandoned wells and their inclusion in greenhouse gas inventories will aid in developing and implementing appropriate greenhouse gas emission reduction strategies.
Scalable detection of statistically significant communities and hierarchies, using message passing for modularity
Authors: Zhang Pan , Moore Cristopher
Published: December 2014

Significance

Most work on community detection does not address the issue of statistical significance, and many algorithms are prone to overfitting. We address this using tools from statistical physics. Rather than trying to find the partition of a network that maximizes the modularity, our approach seeks the consensus of many high-modularity partitions. We do this with a scalable message-passing algorithm, derived by treating the modularity as a Hamiltonian and applying the cavity method. We show analytically that our algorithm succeeds all the way down to the detectability transition in the stochastic block model; it also performs well on real-world networks. It also provides a principled method for determining the number of groups or hierarchies of communities and subcommunities.