bluuebunny/crossref_metadata_2025 huggingface dataset:
Fabrication and measurement of nanostructures on the micro ball surface using a modified atomic force microscope
Authors: Zhao X. S. , Geng Y. Q. , Li W. B. , Yan Y. D. , Hu Z. J. , Sun T. , Liang Y. C. , Dong S.
Published: November 2012

In order to machine and measure nanostructures on the micro ball surface, a modified atomic force microscope (AFM) combining a commercial AFM system with a home built precision air bearing spindle is established. Based on this system, motions of both the AFM scanner and the air bearing spindle are controlled to machine nanostructures on the micro ball based on the AFM tip-based nano mechanical machining approach. The eccentric error between the axis of the micro ball and the axis of the spindle is reduced to 3–4 μm by the provided fine adjusting method. A 1000 nano lines array, 36 square pits structure, 10 square pits structure, and a zig-zag structure on the circumference of the micro ball with the diameter of 1.5 mm are machined successfully. The measurement results achieved by the same system reveal that the profiles and mode-power spectra curves of the micro ball are influenced by the artificially machined nanostructures significantly according to their distributions. This work is an useful attempt for modifying the micro ball profile and manufacture of the spherical modulation targets to study the experimental performance of the micro ball in implosion.
Enhancement of Ag cluster mobility on Ag surfaces by chloridation
Authors: Wu Yu-Ning , Kébaïli Nouari , Cheng Hai-Ping , Cahuzac Philippe , Masson Albert , Bréchignac Catherine
Published: November 2012

To understand the role of chlorine in the stability and the observed fragmentation of Ag dendritic nanostructures, we have studied computationally two model systems using density functional theory. The first one relates to diffusion of \documentclass[12pt]{minimal}\begin{document}$\textrm {Ag}_n$\end{document} Ag n and \documentclass[12pt]{minimal}\begin{document}$\textrm {Ag}_n\textrm {Cl}_m$\end{document} Ag n Cl m (n = 1–4) clusters on an \documentclass[12pt]{minimal}\begin{document}$\textrm {Ag}(111)$\end{document} Ag (111) surface, and the second demonstrates interaction strength of \documentclass[12pt]{minimal}\begin{document}$(\textrm {Ag}_{55})_2$\end{document}( Ag 55)2 dimers with and without chloridation. Based on our calculated energy barriers, \documentclass[12pt]{minimal}\begin{document}$\textrm {Ag}_n\textrm {Cl}_m$\end{document} Ag n Cl m clusters are more mobile than \documentclass[12pt]{minimal}\begin{document}$\textrm {Ag}_n$\end{document} Ag n clusters for n = 1–4. The binding energy between two \documentclass[12pt]{minimal}\begin{document}$\textrm {Ag}_{55}$\end{document} Ag 55 clusters is significantly reduced by surface chloridation. Bond weakening and enhanced mobility are two important mechanisms underlying corrosion and fragmentation processes.
First-principles study on the effective masses of zinc-blend-derived Cu2Zn−IV−VI4 (IV = Sn, Ge, Si and VI = S, Se)
Authors: Liu Heng-Rui , Chen Shiyou , Zhai Ying-Teng , Xiang H. J. , Gong X. G. , Wei Su-Huai
Published: November 2012

The electron and hole effective masses of kesterite (KS) and stannite (ST) structured Cu2Zn−IV−VI4 (IV = Sn, Ge, Si and VI = S, Se) semiconductors are systematically studied using first-principles calculations. We find that the electron effective masses are almost isotropic, while strong anisotropies are observed for the hole effective masses. The electron effective masses are typically much smaller than the hole effective masses for all studied compounds. The ordering of the topmost three valence bands and the corresponding hole effective masses of the KS and ST structures are different due to the different sign of the crystal-field splitting. The electron and hole effective masses of Se-based compounds are significantly smaller compared to the corresponding S-based compounds. They also decrease as the atomic number of the group IV elements (Si, Ge, Sn) increases, but the decrease is less notable than that caused by the substitution of S by Se.
Single crystal of LiInSe2 semiconductor for neutron detector
Authors: Tupitsyn E. , Bhattacharya P. , Rowe E. , Matei L. , Groza M. , Wiggins B. , Burger A. , Stowe A.
Published: November 2012

Single crystals of semiconductor-grade lithium indium selenide (LiInSe2) were grown using the vertical Bridgman method. The orthorhombic structure of the materials was verified using powder x-ray diffraction. The room temperature band gap of the crystal was found to be 2.85 eV using optical absorption measurements. Resistivity of LiInSe2, obtained using current-voltage measurements, has semiconducting nature (decreases with increasing temperature) and is in order of 1010 Ω·cm. Photoconductivity measurement showed the photocurrent peak at 445 nm. Nuclear radiation devices were fabricated, and alpha particle detection was observed, suggesting that this material could be a candidate for neutron detection applications.
Vibrational quenching of excitonic splittings in H-bonded molecular dimers: Adiabatic description and effective mode approximation
Authors: Kopec Sabine , Ottiger Philipp , Leutwyler Samuel , Köppel Horst
Published: November 2012

The quenching of the excitonic splitting in hydrogen-bonded molecular dimers has been explained recently in terms of exciton coupling theory, involving Förster's degenerate perturbation theoretical approach [P. Ottiger, S. Leutwyler, and H. Köppel, J. Chem. Phys. 136, 174308 (2012)10.1063/1.4705119]. Here we provide an alternative explanation based on the properties of the adiabatic potential energy surfaces. In the proper limit, the lower of these surfaces exhibits a double-minimum shape, with an asymmetric distortion that destroys the geometric equivalence of the excitonically coupled monomers. An effective mode is introduced that exactly reproduces the energy gain and amount of distortion that occurs in a multi-dimensional normal coordinate space. This allows to describe the quenched exciton splitting as the energy difference of the two (S1 and S2) vibronic band origins in a one-dimensional (rather than multi-dimensional) vibronic calculation. The agreement with the earlier result (based on Förster theory) is excellent for all five relevant cases studied. A simple rationale for the quenched exciton splitting as nonadiabatic tunneling splitting on the lower double-minimum potential energy surface is given.
Simulations of structural and dynamic anisotropy in nano-confined water between parallel graphite plates
Authors: Mosaddeghi Hamid , Alavi Saman , Kowsari M. H. , Najafi Bijan
Published: November 2012

We use molecular dynamics simulations to study the structure, dynamics, and transport properties of nano-confined water between parallel graphite plates with separation distances (H) from 7 to 20 Å at different water densities with an emphasis on anisotropies generated by confinement. The behavior of the confined water phase is compared to non-confined bulk water under similar pressure and temperature conditions. Our simulations show anisotropic structure and dynamics of the confined water phase in directions parallel and perpendicular to the graphite plate. The magnitude of these anisotropies depends on the slit width H. Confined water shows “solid-like” structure and slow dynamics for the water layers near the plates. The mean square displacements (MSDs) and velocity autocorrelation functions (VACFs) for directions parallel and perpendicular to the graphite plates are calculated. By increasing the confinement distance from H = 7 Å to H = 20 Å, the MSD increases and the behavior of the VACF indicates that the confined water changes from solid-like to liquid-like dynamics. If the initial density of the water phase is set up using geometric criteria (i.e., distance between the graphite plates), large pressures (in the order of ∼10 katm), and large pressure anisotropies are established within the water. By decreasing the density of the water between the confined plates to about 0.9 g cm−3, bubble formation and restructuring of the water layers are observed.
Controlling the column spacing in isothermal magnetic advection to enable tunable heat and mass transfer
Authors: Solis Kyle J. , Martin James E.
Published: November 2012

Isothermal magnetic advection (IMA) is a recently discovered method of inducing highly organized, non-contact flow lattices in suspensions of magnetic particles, using only uniform ac magnetic fields of modest strength. The initiation of these vigorous flows requires neither a thermal gradient nor a gravitational field, and so can be used to transfer heat and mass in circumstances where natural convection does not occur. These advection lattices are comprised of a square lattice of antiparallel flow columns. If the column spacing is sufficiently large compared to the column length and the flow rate within the columns is sufficiently large, then one would expect efficient transfer of both heat and mass. Otherwise, the flow lattice could act as a countercurrent heat exchanger and only mass will be efficiently transferred. Although this latter case might be useful for feeding a reaction front without extracting heat, it is likely that most interest will be focused on using IMA for heat transfer. In this paper, we explore the various experimental parameters of IMA to determine which of these can be used to control the column spacing. These parameters include the field frequency, strength, and phase relation between the two field components, the liquid viscosity, and particle volume fraction. We find that the column spacing can easily be tuned over a wide range to enable the careful control of heat and mass transfer.
A 490 GHz planar circuit balanced Nb-Al2O3-Nb quasiparticle mixer for radio astronomy: Application to quantitative local oscillator noise determination
Authors: Peter Westig Marc , Justen Matthias , Jacobs Karl , Stutzki Jürgen , Schultz Michael , Schomacker Florian , Honingh Netty
Published: November 2012

This article presents a heterodyne experiment which uses a 380–520 GHz planar circuit balanced Nb-Al2O3-Nb superconductor-insulator-superconductor (SIS) quasiparticle mixer with 4–8 GHz instantaneous intermediate frequency (IF) bandwidth to quantitatively determine local oscillator (LO) noise. A balanced mixer is a unique tool to separate noise at the mixer's LO port from other noise sources. This is not possible in single-ended mixers. The antisymmetric IV characteristic of a SIS mixer further helps to simplify the measurements. The double-sideband receiver sensitivity of the balanced mixer is 2–4 times the quantum noise limit hν/kB over the measured frequencies with a maximum LO noise rejection of 15 dB. This work presents independent measurements with three different LO sources that produce the reference frequency but also an amount of near-carrier noise power which is quantified in the experiment as a function of the LO and IF frequency in terms of an equivalent noise temperature TLO. Two types of LO sources are used: a synthesizer driven amplifier/multiplier chain and a Gunn oscillator driven multiplier chain. With the first type of LO we find different near-carrier noise contributions using two different power pre-amplifiers of the LO system. For one of the two power pre-amplifiers we measure TLO=30±4 K at the LO frequency 380 GHz and TLO=38±10 K at 420 GHz. At the frequency band center 465 GHz of the Gunn driven LO we measure a comparable value of TLO=32±6 K. For the second power pre-amplifier, a significant higher TLO value of the synthesizer driven LO is found which is up to six times larger compared with the best values found for the Gunn driven LO. In a second experiment, we use only one of two SIS mixers of the balanced mixer chip in order to verify the influence of near-carrier LO noise power on a single-ended heterodyne mixer measurement. We find an IF frequency dependence of near-carrier LO noise power. The frequency-resolved IF noise temperature slope is flat or slightly negative for the single-ended mixer. This is in contrast to the IF slope of the balanced mixer itself which is positive due to the expected IF roll-off of the mixer. This indicates a higher noise level closer to the LO's carrier frequency. Our findings imply that near-carrier LO noise has the largest impact on the sensitivity of a receiver system which uses mixers with a low IF band, for example, superconducting hot-electron bolometer HEB mixers.
Relaxation and critical strain for maximum In incorporation in AlInGaN on GaN grown by metal organic vapour phase epitaxy
Authors: Reuters Benjamin , Finken M. , Wille A. , Holländer B. , Heuken M. , Kalisch H. , Vescan A.
Published: November 2012

Quaternary AlInGaN layers were grown on conventional GaN buffer layers on sapphire by metal organic vapour phase epitaxy at different surface temperatures and different reactor pressures with constant precursor flow conditions. A wide range in compositions within 30–62% Al, 5–29% In, and 23–53% Ga was covered, which leads to different strain states from high tensile to high compressive. From high-resolution x-ray diffraction and Rutherford backscattering spectrometry, we determined the compositions, strain states, and crystal quality of the AlInGaN layers. Atomic force microscopy measurements were performed to characterize the surface morphology. A critical strain value for maximum In incorporation near the AlInGaN/GaN interface is presented. For compressively strained layers, In incorporation is limited at the interface as residual strain cannot exceed an empirical critical value of about 1.1%. Relaxation occurs at about 15 nm thickness accompanied by strong In pulling. Tensile strained layers can be grown pseudomorphically up to 70 nm at a strain state of 0.96%. A model for relaxation in compressively strained AlInGaN with virtual discrete sub-layers, which illustrates the gradually changing lattice constant during stress reduction is presented.
Surface effects on the radiation response of nanoporous Au foams
Authors: Fu E. G. , Caro M. , Zepeda-Ruiz L. A. , Wang Y. Q. , Baldwin K. , Bringa E. , Nastasi M. , Caro A.
Published: November 2012

We report on an experimental and simulation campaign aimed at exploring the radiation response of nanoporous Au (np-Au) foams. We find different defect accumulation behavior by varying radiation dose-rate in ion-irradiated np-Au foams. Stacking fault tetrahedra are formed when np-Au foams are irradiated at high dose-rate, but they do not seem to be formed in np-Au at low dose-rate irradiation. A model is proposed to explain the dose-rate dependent defect accumulation based on these results.
Fabrication of metallic double-gate field emitter arrays and their electron beam collimation characteristics
Authors: Helfenstein P. , Jefimovs K. , Kirk E. , Escher C. , Fink H.-W. , Tsujino S.
Published: November 2012

The fabrication of double-gate metallic field emitter arrays with large collimation gate apertures and their field emission beam characteristics are reported. The device fabrication steps, including the molding technique for array fabrication, the electron extraction gate fabrication by the self-aligned resist etch-back method, and the fabrication of the collimation gate electrode using a focused ion beam assisted method are described in detail. The experimental results of 2 × 2 tip arrays with the proposed double-gate structure demonstrate an order of magnitude enhancement in beam brightness with minimal current loss. A similarly high beam brightness enhancement was achieved with a 20 × 20 tip array device, showing the scalability of the proposed structure. The observation of improved current-voltage characteristics with the 20 × 20 tip array is ascribed to the difference in gate aperture shape. The possibility of further improving the beam characteristics of double-gate field emitter arrays and the reduction of the transverse electron velocity spread are discussed.
Forward and back energy transfer between Cu2+ and Yb3+ in Ca1−xCuSi4O10:Ybx crystals
Authors: Zhuang Yixi , Tanabe Setsuhisa
Published: November 2012

We report on near-infrared photoluminescence studies in Ca1−xCuSi4O10: Ybx (x = 0.00 − 0.10) polycrystals by means of diffuse reflection, photoluminescence, excitation spectra and luminescence decay analysis. The samples show intense absorption bands at 540, 630, 800 nm due to Cu2+: 2B1g→2A1g, 2Eg, 2B2g transitions. Under the excitation, the samples show efficient photoluminescence at 920 nm from Cu2+ and 1007 nm from Yb3+, respectively. With increasing of Yb concentration, the PL intensity of Yb3+ increases obviously, while that of the Cu2+ decreases slightly. A probable energy transfer mechanism can be proposed on the basis of decay curves and temperature-dependent photoluminescence spectra.
Simulating protein unfolding under pressure with a coarse-grained model
Authors: Perezzan Ramiro , Rey Antonio
Published: November 2012

We describe and test a coarse-grained molecular model for the simulation of the effects of pressure on the folding/unfolding transition of proteins. The model is a structure-based one, which takes into account the desolvation barrier for the formation of the native contacts. The pressure is taken into account in a qualitative, mean field approach, acting on the parameters describing the native stabilizing interactions. The model has been tested by simulating the thermodynamic and structural behavior of protein GB1 with a parallel tempering Monte Carlo algorithm. At low effective pressures, the model reproduces the standard two-state thermal transition between the native and denatured states. However, at large pressures a new state appears. Its structural characteristics have been analyzed, showing that it corresponds to a swollen version of the native structure. This swollen state is at equilibrium with the native state at low temperatures, but gradually transforms into the thermally denatured state as temperature is increased. Therefore, our model predicts a downhill transition between the swollen and the denatured states. The analysis of the model permits us to obtain a phase diagram for the pressure-temperature behavior of the simulated system, which is compatible with the known elliptical shape of this diagram for real proteins.
Nano-environment effects on the luminescence properties of Eu3+-doped nanocrystalline SnO2 thin films
Authors: Bazargan Samad , Leung K. T.
Published: November 2012

Nanocrystalline tin (IV) oxide thin films doped with Eu3+ ions are synthesized using a simple spin-coating method followed by postannealing in an O2 flow at 700 °C. Transmission electron microscopy and x-ray photoelectron spectroscopy studies illustrate the incorporation of Eu3+ ions in the films with a high atomic percentage of 2.7%–7.7%, which is found to be linearly dependent on the initial concentration of Eu3+ in the precursor solution. Glancing incidence x-ray diffraction results show that the crystalline grain sizes decrease with increasing the Eu3+ concentration and decreasing the postannealing temperature with the emergence of the Eu2Sn2O7 phase at high Eu3+ concentrations (≥5.3 at.%). Luminescence spectra of these doped samples show the characteristic narrow-band magnetic dipole emission at 593 nm and electric dipole emission at 614 nm of the Eu3+ ions, arising from UV absorption at the SnO2 band-edge followed by energy transfer to the emission centers. Manipulating the crystallite size, composition, and defect density of the samples greatly affects the absorption edge, energy transfer, and therefore the emission spectra. These modifications in the environment of the Eu3+ ions allow the emission to be tuned from pure orange characteristic Eu3+ emission to the broadband emission corresponding to the combination of strong characteristic Eu3+ emission with the intense defect emissions.
Polymorphic phases of sp3-hybridized superhard CN
Authors: Wang Xiaoli
Published: November 2012

It is well established that carbon nitride (CN) is a potential superhard material as its bond in network structures is slightly shorter than the C–C bond in diamond. However, the structure of superhard CN materials is yet to be determined experimentally. We have performed an extensive structural search for the high pressure crystalline phases of CN using the particle swarm optimization technique; seven low-energy polymorphic structures of sp3-hybridized CN have been found in an unbiased search. Density-functional theory calculations indicate that, among the seven low-energy crystalline structures, Pnnm structure (8 atoms/cell) is energetically more favorable than the previously reported most stable crystalline structure with 1:1 stoichiometry. Furthermore, Pnnm possesses the highest hardness (62.3 GPa). Formation enthalpies demonstrate that this material can be synthesized at pressure 10.9 GPa, lower than needed by β-C3N4 (14.1 GPa).
Transition from laminar to three-dimensional growth mode in pulsed laser deposited BiFeO3 film on (001) SrTiO3
Authors: Chinta Priya V. , Callori Sara J. , Dawber Matthew , Ashrafi Almamun , Headrick Randall L.
Published: November 2012

Real-time specular x-ray reflectivity of pulsed laser deposited BiFeO3 films exhibits unit-cell oscillations, with diffuse scattering intensity out-of-phase with the specular intensity. The growth mode is thus identified as nucleation and coalescence of unit-cell height islands. The growth rate is insensitive to the deposition rate, suggesting self-limiting growth. Beyond several monolayers the diffuse intensity increases abruptly, signaling a transition from two-dimensional to three-dimensional growth. Ex situ atomic force microscopy shows that mounds merge after a few more deposited layers, leaving arrays of mesas with some holes due to incomplete coalescence.
Spinodal assisted growing dynamics of critical nucleus in polymer blends
Authors: Zhang Xinghua , Qi Shuanhu , Yan Dadong
Published: November 2012

In metastable polymer blends, nonclassical critical nucleus is not a drop of stable phase in core wrapped with a sharp interface, but a diffuse structure depending on the metastability. Thus, forming a critical nucleus does not mean the birth of a new phase. In the present work, the nonclassical growing dynamics of the critical nucleus is addressed in the metastable polymer blends by incorporating self-consistent field theory and external potential dynamics theory, which leads to an intuitionistic description for the scattering experiments. The results suggest that the growth of nonclassical critical nucleus is controlled by the spinodal-decomposition which happens in the region surrounding the nucleus. This leads to forming the shell structures around the nucleus.
Why do atomic force microscopy force curves still exhibit jump to contact?
Authors: Rodrigues Mario S. , Costa Luca , Chevrier Joël , Comin Fabio
Published: November 2012

The force between two particles as a function of distance is one of the most fundamental curves in physics. Here, we describe how the force feedback microscope can routinely measure the tip-surface interaction in the entire range of distances with a sensitivity of 1 pN and in different media. The method allows to measure simultaneously the force, force gradient, and damping from solely the knowledge of the lever spring constant. The jump to contact is avoided and thus it is possible to follow the brutal nucleation of a water bridge between the tip and the surface.
Current-induced nanogap formation and graphitization in boron-doped diamond films
Authors: Seshan V. , Arroyo C. R. , Castellanos-Gomez A. , Prins F. , Perrin M. L. , Janssens S. D. , Haenen K. , Nesládek M. , Sudhölter E. J. R. , de Smet L. C. P. M. , van der Zant H. S. J. , Dulic D.
Published: November 2012

A high-current annealing technique is used to fabricate nanogaps and hybrid diamond/graphite structures in boron-doped nanocrystalline diamond films. Nanometer-sized gaps down to ∼1 nm are produced using a feedback-controlled current annealing procedure. The nanogaps are characterized using scanning electron microscopy and electronic transport measurements. The structural changes produced by the elevated temperature, achieved by Joule heating during current annealing, are characterized using Raman spectroscopy. The formation of hybridized diamond/graphite structure is observed at the point of maximum heat accumulation.
Excited-state thermionic emission in III-antimonides: Low emittance ultrafast photocathodes
Authors: Berger Joel A. , Rickman B. L. , Li T. , Nicholls A. W. , Andreas Schroeder W.
Published: November 2012

The normalized rms transverse emittance of an electron source is shown to be proportional to m*, where m* is the effective mass of the state from which the electron is emitted, by direct observation of the transverse momentum distribution for excited-state thermionic emission from two III-V semiconductor photocathodes, GaSb and InSb, together with a control experiment employing two-photon emission from gold. Simulations of the experiment using an extended analytical Gaussian model of electron pulse propagation are in close agreement with the data.
Charge-leveling and proper treatment of long-range electrostatics in all-atom molecular dynamics at constant pH
Authors: Wallace Jason A. , Shen Jana K.
Published: November 2012

Recent development of constant pH molecular dynamics (CpHMD) methods has offered promise for adding pH-stat in molecular dynamics simulations. However, until now the working pH molecular dynamics (pHMD) implementations are dependent in part or whole on implicit-solvent models. Here we show that proper treatment of long-range electrostatics and maintaining charge neutrality of the system are critical for extending the continuous pHMD framework to the all-atom representation. The former is achieved here by adding forces to titration coordinates due to long-range electrostatics based on the generalized reaction field method, while the latter is made possible by a charge-leveling technique that couples proton titration with simultaneous ionization or neutralization of a co-ion in solution. We test the new method using the pH-replica-exchange CpHMD simulations of a series of aliphatic dicarboxylic acids with varying carbon chain length. The average absolute deviation from the experimental pKa values is merely 0.18 units. The results show that accounting for the forces due to extended electrostatics removes the large random noise in propagating titration coordinates, while maintaining charge neutrality of the system improves the accuracy in the calculated electrostatic interaction between ionizable sites. Thus, we believe that the way is paved for realizing pH-controlled all-atom molecular dynamics in the near future.
Plasma focus ion beam fluence and flux—Scaling with stored energy
Authors: Lee S. , Saw S. H.
Published: November 2012

Measurements on plasma focus ion beams include various advanced techniques producing a variety of data which has yet to produce benchmark numbers [A Bernard et al., J. Mosc. Phys. Soc. 8, 93-170 (1998)]. This present paper uses the Lee Model code [S Lee, http://www.plasmafocus.net (2012)], integrated with experimental measurements to provide the basis for reference numbers and the scaling of deuteron beams versus stored energy E0. The ion number fluence (ions m−2) and energy fluence (J m−2) computed as 2.4−7.8 × 1020 and 2.2−33 × 106, respectively, are found to be independent of E0 from 0.4 to 486 kJ. Typical inductance machines (33–55 nH) produce 1.2−2 × 1015 ions per kJ carrying 1.3%–4% E0 at mean ion energy 50–205 keV, dropping to 0.6 × 1015 ions per kJ carrying 0.7% E0 for the high inductance INTI PF.
Volumetric measurements of a spatially growing dust acoustic wave
Authors: Williams Jeremiah D.
Published: November 2012

In this study, tomographic particle image velocimetry (tomo-PIV) techniques are used to make volumetric measurements of the dust acoustic wave (DAW) in a weakly coupled dusty plasma system in an argon, dc glow discharge plasma. These tomo-PIV measurements provide the first instantaneous volumetric measurement of a naturally occurring propagating DAW. These measurements reveal over the measured volume that the measured wave mode propagates in all three spatial dimensional and exhibits the same spatial growth rate and wavelength in each spatial direction.
Effects of ocean thermal energy conversion systems on near and far field seawater properties—A case study for Hawaii
Authors: Jia Yanli , Nihous Gérard C. , Richards Kelvin J.
Published: November 2012

In light of renewed interest and efforts in the development of ocean thermal energy conversion (OTEC) systems with a vision to provide mankind with a long-lasting energy resource, the potential environmental impacts of this technology should be considered from the perspective of sustainability. As an important step toward such a goal, we examine effects of OTEC effluent discharge on the physical aspects of the ocean environment near a Hawaiian Island in the North Pacific Ocean. We use modeling tools comprised of a mixing model that predicts the near field dilution of effluent plumes and a high-resolution ocean circulation model that simulates the dispersion of effluent in the far field. Numerical experiments are conducted to explore factors that influence effluent dispersal. We find that OTEC thermal resource is favorable and stable at the chosen location for the time period experimented. For a given OTEC design, the effluent discharge settles at a depth sufficiently far from the depths of discharge or intakes, and becomes dispersed quickly away from the site by highly variable ocean currents. Changes in ocean stratification and flow field are negligible for one OTEC device but are notable when multiple OTEC devices are present. These changes do not persist beyond 2 weeks after switching off OTEC activity.
A review on frequency tuning methods for piezoelectric energy harvesting systems
Authors: Ibrahim Sutrisno W. , Ali Wahied G.
Published: November 2012

Piezoelectric energy harvesting technologies have received a great attention during the last decade to design self-powered microelectronic devices such as wireless sensor nodes. Piezoelectric energy harvester is a resonant system that produces maximum power output when its resonant frequency matches the ambient vibration frequency. The deviation from the resonance causes significant decrease in the power output. There are two possible solutions to compensate the effect of frequency deviation: widening the operating frequency bandwidth and tuning the resonant frequency. Tuning the resonant frequency is a more efficient technique for applications with single time varying dominant frequency. This paper presents a comprehensive review of frequency tuning methods for piezoelectric energy harvesting systems. Two categories generally investigated in the literature include manual and autonomous tuning methods. The recent developments of many tuning strategies are discussed and summarized.
Phase space structure of the electron diffusion region in reconnection with weak guide fields
Authors: Ng J. , Egedal J. , Le A. , Daughton W.
Published: November 2012

Kinetic simulations of magnetic reconnection provide detailed information about the electric and magnetic structure throughout the simulation domain, as well as high resolution profiles of the essential fluid parameters including the electron and ion densities, flows, and pressure tensors. However, the electron distribution function, f(v), within the electron diffusion region becomes highly structured in the three dimensional velocity space and is not well resolved by the data available from the particle-in-cell (PIC) simulations. Here, we reconstruct the electron distribution function within the diffusion region at enhanced resolution. This is achieved by tracing electron orbits in the fields taken from PIC simulations back to the inflow region where an analytic form of the magnetized electron distribution is known. For antiparallel reconnection, the analysis reveals the highly structured nature of f(v), with striations corresponding to the number of times electrons have been reflected within the reconnection current layer, and exposes the origin of gradients in the electron pressure tensor important for momentum balance. The structure of the reconnection region is strongly tied to the pressure anisotropy that develops in the electrons upstream of the reconnection region. The addition of a guide field changes the nature of the electron distributions, and the differences are accounted for by studying the motion of single particles in the field geometry. Finally, the geometry of small guide field reconnection is shown to be highly sensitive to the ion/electron mass ratio applied in the simulation.
Optimization of surface morphology to reduce the effect of grain boundaries and contact resistance in small molecule based thin film transistors
Authors: Yadav Sarita , Kumar Pramod , Ghosh Subhasis
Published: November 2012

Grain boundaries in organic thin film have been controlled by engineering the different growth conditions in such a way that it reduces the contact resistance and enhances the carrier mobility in p-type copper phthalocyanine and n-type copper hexadecafluoro phthalocyanine based organic thin film transistors. Reduced effect of grain boundary has been demonstrated by temperature dependence of charge carrier mobility and other transport parameters. A correlation has been established between contact resistance and certain thin film morphology, achieved by varying different growth conditions.
Dynamics of cellular response to hypotonic stimulation revealed by quantitative phase microscopy and multi-fractal detrended fluctuation analysis
Authors: Cardenas Nelson , Kumar Satish , Mohanty Samarendra
Published: November 2012

Hypotonic stimulation is known to cause morphological changes in cells and also leads to modulation of cellular physiology. In order to evaluate the dynamics of cellular response to hypotonic stimulation, we utilized digital holographic microscopy for quantitative phase microscopy, achieved by a common-path interferometry geometry based on extraction of reference beam by spatial-filtering. Results from live cell investigations demonstrate the capability of this method for dynamic quantitative phase imaging. Further, wavelet and multi-fractal detrended fluctuation analysis revealed that the dynamic phase changes, in response to hypotonic stimulation, are multifractal in nature.
Ultrafast laser orthogonal alignment and patterning of carbon nanotube-polymer composite films
Authors: Murphy Ryan D. , Abere Michael J. , Zhang Huanan , Sun Haiping , Torralva Ben , Mansfield John F. , Kotov Nicholas A. , Yalisove Steven M.
Published: November 2012

Dual orthogonal alignment of carbon nanotubes (CNTs) within the plane and perpendicular to a substrate is essential for many applications but difficult to obtain. Here, we demonstrate that it is possible using a combination of layer-by-layer deposition and ultrafast laser irradiation. Single-wall CNT-polymer composites preferentially aligned within the plane are irradiated with ultrafast laser pulses. After irradiation with distinct fluences at ambient conditions, morphology is seen where CNTs are formed into bundled CNTs with some orthogonal alignment. A model is presented to account for thermal expansion of the polymer and the formation of CNT bundles.
Compression studies of face-to-face π-stacking interaction in sodium squarate salts: Na2C4O4 and Na2C4O4•3H2O
Authors: Li Qian , Li Shourui , Wang Kai , Li Wenbo , Liu Jing , Liu Bingbing , Zou Guangtian , Zou Bo
Published: November 2012

High-pressure Raman scattering and synchrotron X-ray diffraction measurements of sodium squarate (Na2C4O4, SS) are performed in a diamond anvil cell. SS possesses a rare, but typical structure, which can show the effect of face-to-face π-stacking without interference of other interactions. At ∼11 GPa, it undergoes a phase transition, identified as a symmetry transformation from P21/c to P21. From high-pressure Raman patterns and the calculated model of SS, it can be proved that the phase transition results from the distorted squarate rings. We infer it is the enhancement of π-stacking that dominates the distortion. For comparison, high-pressure Raman spectra of sodium squarate trihydrate (Na2C4O4•3H2O, SST) are also investigated. The structure of SST is determined by both face-to-face π-stacking and hydrogen bonding. SST can be regarded as a deformation of SS. A phase transition, with the similar mechanism as SS, is observed at ∼10.3 GPa. Our results can be well supported by the previous high-pressure studies of ammonium squarate ((NH4)2C4O4, AS), and vice versa. High-pressure behaviors of the noncovalent interactions in SS, SST, and AS are compared to show the impacts of hydrogen bonding and the role of electrostatic interaction in releasing process.
Optical logic gates using coherent feedback
Authors: Zhou Zhifan , Liu Cunjin , Fang Yami , Zhou Jun , Glasser Ryan T. , Chen Liqing , Jing Jietai , Zhang Weiping
Published: November 2012

We experimentally demonstrate optical logic “or” and “nor” gates via coherent feedback. Based on a four-wave mixing process in hot rubidium vapor, two feedback beams are capable of fulfilling an optical “nor” gate for the feedback-suppressed state and an optical “or” gate for the feedback-boosted state simultaneously. The logic gates exhibit transition times faster than previously demonstrated in rubidium vapor. Coherent photon conversion between the two logic states, due to the atomic coherence, is observed in the coherent feedback process.
High-efficiency spoof plasmon polariton coupler mediated by gradient metasurfaces
Authors: Wang Jiafu , Qu Shaobo , Ma Hua , Xu Zhuo , Zhang Anxue , Zhou Hang , Chen Hongya , Li Yongfeng
Published: November 2012

Gradient metasurfaces (GMs) can provide pre-defined wave vectors that are along the surface of GMs. When the additional wave vector is greater than that of incident waves, the incident waves can be coupled efficiently as spoof plasmon polaritons (SPPs) even under normal incidence. In this Letter, the design of SPP couplers was proposed based on GMs. A high-efficiency SPP coupler was designed using split-ring resonators. Both the simulation and experiment show that the GM can achieve nearly perfect SPP-coupling under normal incidence at the designed frequency.
Quantitative analysis of electric field induced change in anisotropy field in Co60Fe20B20/(011) xPb(Mg1/3Nb2/3)O3-(1 − x)PbTiO3 (x ∼ 0.68) heterostructures
Authors: Zhu Guodong , Wong Kin L. , Zhao Jing , Amiri Pedram Khalili , Zhu Jian , Krivorotov Ilya , Wang Kang L.
Published: November 2012

Electric modulation of spin waves in ferroelectric/ferromagnetic heterostructures has attracted much attention due to its potential in spin wave devices. In this letter, we report our work on quantitating the electric field induced modulation of spin wave frequency and anisotropy field in CoFeB/xPb(Mg1/3Nb2/3)O3-(1 − x)PbTiO3 (x ∼ 0.68) composite structure by propagating spin wave spectroscopy (PSWS) technique. To verify the reliability of PSWS measurements, magneto-optical Kerr effect measurement is also performed, the result of which is comparable with that from the PSWS measurement.
Plasmon-induced fluorescence and electroluminescence from porphine molecules on GaAs(110) in a scanning tunneling microscope
Authors: Mühlenberend Svenja , Schneider Natalia L. , Gruyters Markus , Berndt Richard
Published: November 2012

Surface plasmon polaritons of the tip of a scanning tunneling microscope are used to induce fluorescence from (5,10,15,20)-tetraphenyl-21 H,23 H-porphine molecules on GaAs(110) surfaces at very low coverages. Fluorescence spectra exhibiting vibrationally resolved Q-band transitions show that the luminescence is of molecular origin. The emission is not directly induced by the tunneling current. Rather, radiationless energy transfer from plasmon modes of the tip leads to molecular excitation.
Nanoindentation study on insight of plasticity related to dislocation density and crystal orientation in GaN
Authors: Fujikane Masaki , Yokogawa Toshiya , Nagao Shijo , Nowak Roman
Published: November 2012

Yield shear stress dependence on dislocation density and crystal orientation was studied in GaN by nanoindentation examination. The yield shear stress decreased with increasing dislocation density, and it decreased with decreasing nanoindentation strain-rate. It reached and coincided at 11.5 GPa for both quasi-static deformed c-plane and m-plane GaN. Taking into account theoretical Peierls–Nabarro stress and yield stress for each slip system, these phenomena were concluded to be an evidence of heterogeneous mechanism associated plastic deformation in GaN crystal. Transmission electron microscopy and molecular dynamics simulation also supported the mechanism with obtained r-plane dislocation line.
Orbital characters and near two-dimensionality of Fermi surfaces in NaFe1−xCoxAs
Authors: Liu Z.-H. , Richard P. , Li Y. , Jia L.-L. , Chen G.-F. , Xia T.-L. , Wang D.-M. , He J.-B. , Yang H.-B. , Pan Z.-H. , Valla T. , Johnson P. D. , Xu N. , Ding H. , Wang S.-C.
Published: November 2012

We report a comprehensive study of orbital characters and tridimensional nature of the electronic bands of 111-family in Fe-pnictides superconductors, NaFe1−xCoxAs (x = 0 and 0.05), with angle-resolved photoemission spectroscopy. We determined the orbital characters and the kz dependence of the low-energy electronic structures by tuning the polarization and the energy of the incident photons. We observed two nearly two-dimensional hole-like Fermi surfaces (FS) near the Brillouin zone (BZ) center and two electron-like FS near BZ corner. The bands near the Fermi level (EF) are mainly derived from the Fe 3dxy, 3dyz, and 3dzx orbitals.
Carbon and other light element contents in the Earth’s core based on first-principles molecular dynamics
Authors: Zhang Yigang , Yin Qing-Zhu
Published: November 2012

Carbon (C) is one of the candidate light elements proposed to account for the density deficit of the Earth’s core. In addition, C significantly affects siderophile and chalcophile element partitioning between metal and silicate and thus the distribution of these elements in the Earth’s core and mantle. Derivation of the accretion and core–mantle segregation history of the Earth requires, therefore, an accurate knowledge of the C abundance in the Earth’s core. Previous estimates of the C content of the core differ by a factor of ∼20 due to differences in assumptions and methods, and because the metal–silicate partition coefficient of C was previously unknown. Here we use two-phase first-principles molecular dynamics to derive this partition coefficient of C between liquid iron and silicate melt. We calculate a value of 9 ± 3 at 3,200 K and 40 GPa. Using this partition coefficient and the most recent estimates of bulk Earth or mantle C contents, we infer that the Earth’s core contains 0.1–0.7 wt% of C. Carbon thus plays a moderate role in the density deficit of the core and in the distribution of siderophile and chalcophile elements during core–mantle segregation processes. The partition coefficients of nitrogen (N), hydrogen, helium, phosphorus, magnesium, oxygen, and silicon are also inferred and found to be in close agreement with experiments and other geochemical constraints. Contents of these elements in the core derived from applying these partition coefficients match those derived by using the cosmochemical volatility curve and geochemical mass balance arguments. N is an exception, indicating its retention in a mantle phase instead of in the core.
Multimodal imaging of the self-regulating developing brain
Authors: Fjell Anders M. , Walhovd Kristine Beate , Brown Timothy T. , Kuperman Joshua M. , Chung Yoonho , Hagler Donald J. , Venkatraman Vijay , Roddey J. Cooper , Erhart Matthew , McCabe Connor , Akshoomoff Natacha , Amaral David G. , Bloss Cinnamon S. , Libiger Ondrej , Darst Burcu F. , Schork Nicholas J. , Casey B. J. , Chang Linda , Ernst Thomas M. , Gruen Jeffrey R. , Kaufmann Walter E. , Kenet Tal , Frazier Jean , Murray Sarah S. , Sowell Elizabeth R. , van Zijl Peter , Mostofsky Stewart , Jernigan Terry L. , Dale Anders M. , Jernigan Terry L. , McCabe Connor , Chang Linda , Akshoomoff Natacha , Newman Erik , Dale Anders M. , Ernst Thomas , Dale Anders M. , Van Zijl Peter , Kuperman Joshua , Murray Sarah , Bloss Cinnamon , Schork Nicholas J. , Appelbaum Mark , Gamst Anthony , Thompson Wesley , Bartsch Hauke , Jernigan Terry L. , Dale Anders M. , Akshoomoff Natacha , Chang Linda , Ernst Thomas , Keating Brian , Amaral David , Sowell Elizabeth , Kaufmann Walter , Van Zijl Peter , Mostofsky Stewart , Casey B.J. , Ruberry Erika J. , Powers Alisa , Rosen Bruce , Kenet Tal , Frazier Jean , Kennedy David , Gruen Jeffrey
Published: November 2012

Self-regulation refers to the ability to control behavior, cognition, and emotions, and self-regulation failure is related to a range of neuropsychiatric problems. It is poorly understood how structural maturation of the brain brings about the gradual improvement in self-regulation during childhood. In a large-scale multicenter effort, 735 children (4–21 y) underwent structural MRI for quantification of cortical thickness and surface area and diffusion tensor imaging for quantification of the quality of major fiber connections. Brain development was related to a standardized measure of cognitive control (the flanker task from the National Institutes of Health Toolbox), a critical component of self-regulation. Ability to inhibit responses and impose cognitive control increased rapidly during preteen years. Surface area of the anterior cingulate cortex accounted for a significant proportion of the variance in cognitive performance. This finding is intriguing, because characteristics of the anterior cingulum are shown to be related to impulse, attention, and executive problems in neurodevelopmental disorders, indicating a neural foundation for self-regulation abilities along a continuum from normality to pathology. The relationship was strongest in the younger children. Properties of large-fiber connections added to the picture by explaining additional variance in cognitive control. Although cognitive control was related to surface area of the anterior cingulate independently of basic processes of mental speed, the relationship between white matter quality and cognitive control could be fully accounted for by speed. The results underscore the need for integration of different aspects of brain maturation to understand the foundations of cognitive development.
Implantable, multifunctional, bioresorbable optics
Authors: Tao Hu , Kainerstorfer Jana M. , Siebert Sean M. , Pritchard Eleanor M. , Sassaroli Angelo , Panilaitis Bruce J. B. , Brenckle Mark A. , Amsden Jason J. , Levitt Jonathan , Fantini Sergio , Kaplan David L. , Omenetto Fiorenzo G.
Published: November 2012

Advances in personalized medicine are symbiotic with the development of novel technologies for biomedical devices. We present an approach that combines enhanced imaging of malignancies, therapeutics, and feedback about therapeutics in a single implantable, biocompatible, and resorbable device. This confluence of form and function is accomplished by capitalizing on the unique properties of silk proteins as a mechanically robust, biocompatible, optically clear biomaterial matrix that can house, stabilize, and retain the function of therapeutic components. By developing a form of high-quality microstructured optical elements, improved imaging of malignancies and of treatment monitoring can be achieved. The results demonstrate a unique family of devices for in vitro and in vivo use that provide functional biomaterials with built-in optical signal and contrast enhancement, demonstrated here with simultaneous drug delivery and feedback about drug delivery with no adverse biological effects, all while slowly degrading to regenerate native tissue.