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  • 1
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    American Institute of Physics (AIP)
    Online: 1.1991 –
    Publisher: American Institute of Physics (AIP)
    Print ISSN: 1054-1500
    Electronic ISSN: 1089-7682
    Topics: Physics
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  • 2
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    American Institute of Physics (AIP)
    Online: 1.1931 –
    Formerly as: Physics  (1931–1936)
    Publisher: American Institute of Physics (AIP)
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
    Acronym: JAP
    Abbreviation: J Appl Phys
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  • 3
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    American Institute of Physics (AIP)
    Online: 1(1).1989 – 5(12).1993
    Publisher: American Institute of Physics (AIP)
    Print ISSN: 0899-8213
    Topics: Physics
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  • 4
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    American Institute of Physics (AIP)
    Online: 52.1999 –
    Print: 39(7).1986 – 45.1992 (Location: A17, Kompaktmagazin, 58/6-7)
    Print: 44.1991 – 63.2010 (Location: A43, Archiv)
    Print: 46.1993 – 71.2018 (Location: A17, Kompaktmagazin, 58/6-7)
    Publisher: American Institute of Physics (AIP)
    Print ISSN: 0031-9228
    Topics: Physics
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  • 5
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    American Institute of Physics (AIP)
    Online: 1(1).1989 – 5(12).1993
    Publisher: American Institute of Physics (AIP)
    Print ISSN: 0899-8221
    Topics: Physics
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  • 6
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    American Institute of Physics (AIP)
    Online: 1.1994 –
    Publisher: American Institute of Physics (AIP)
    Print ISSN: 1070-664X
    Electronic ISSN: 1089-7674
    Topics: Physics
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  • 7
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    American Institute of Physics (AIP)
    Online: 1.1930 –
    Print: 28.1957 – 41.1970 (Location: A18, ---)
    Formerly as: Review of Scientific Instruments with Physics News and Views  (1933–1938)
    Publisher: American Institute of Physics (AIP)
    Print ISSN: 0034-6748
    Electronic ISSN: 1089-7623
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
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  • 8
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    American Crystallographic Association (ACA) | American Institute of Physics (AIP)
    Online: 1(1).2014 –
    Publisher: American Crystallographic Association (ACA) , American Institute of Physics (AIP)
    Electronic ISSN: 2329-7778
    Topics: Physics
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  • 9
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    American Institute of Physics (AIP)
    Online: 1(1).2016 –
    Publisher: American Institute of Physics (AIP)
    Electronic ISSN: 2378-0967
    Topics: Physics
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  • 10
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    American Institute of Physics (AIP)
    Online: 1.1962 –
    Publisher: American Institute of Physics (AIP)
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
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  • 11
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    American Institute of Physics (AIP)
    Online: 1.1975 – 29.2003
    Publisher: American Institute of Physics (AIP)
    Print ISSN: 0360-0327
    Electronic ISSN: 1063-7737
    Topics: Physics
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  • 12
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    American Institute of Physics (AIP) | IEEE Computer Society | Institute of Electrical and Electronics Engineers (IEEE)
    Online: 1.1999 –
    Publisher: American Institute of Physics (AIP) , IEEE Computer Society , Institute of Electrical and Electronics Engineers (IEEE)
    Print ISSN: 1521-9615
    Electronic ISSN: 1558-366X
    Topics: Computer Science , Natural Sciences in General , Technology
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  • 13
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    American Institute of Physics (AIP)
    Online: 1.1933 –
    Publisher: American Institute of Physics (AIP)
    Print ISSN: 0021-9606
    Electronic ISSN: 1089-7690
    Topics: Chemistry and Pharmacology , Physics
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  • 14
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    American Institute of Physics (AIP)
    Online: 1.1960 –
    Publisher: American Institute of Physics (AIP)
    Print ISSN: 0022-2488
    Electronic ISSN: 1089-7658
    Topics: Mathematics , Physics
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  • 15
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    American Institute of Physics (AIP)
    Online: 23.1997 –
    Publisher: American Institute of Physics (AIP)
    Print ISSN: 1063-777X
    Electronic ISSN: 1090-6517
    Topics: Physics
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  • 16
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    American Institute of Physics (AIP)
    Online: 1.1958 –
    Formerly as: Physics of Fluids A: Fluid Dynamics ; Physics of Fluids B: Plasma Physics  (1989–1993)
    Publisher: American Institute of Physics (AIP)
    Print ISSN: 0031-9171 , 1070-6631
    Electronic ISSN: 1089-7666
    Topics: Physics
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  • 17
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    American Institute of Physics (AIP)
    Online: 36.2004 –
    Publisher: American Institute of Physics (AIP)
    Print ISSN: 0148-5857
    Topics: Physics
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  • 18
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    American Institute of Physics (AIP) | American Crystallographic Association (ACA)
    Online: 1.2011 –
    Publisher: American Institute of Physics (AIP) , American Crystallographic Association (ACA)
    Electronic ISSN: 2158-3226
    Topics: Physics
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  • 19
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    American Institute of Physics (AIP)
    Online: 1.2013 –
    Publisher: American Institute of Physics (AIP)
    Electronic ISSN: 2166-532X
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Keywords: Werkstoffkunde
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  • 20
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    American Institute of Physics (AIP)
    Online: 1.1969 – 34.2002
    Publisher: American Institute of Physics (AIP)
    Print ISSN: 0002-7537
    Topics: Physics
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  • 21
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    American Institute of Physics (AIP)
    Online: 1.2009 –
    Publisher: American Institute of Physics (AIP)
    Electronic ISSN: 1941-7012
    Topics: Energy, Environment Protection, Nuclear Power Engineering
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  • 22
    Publication Date: 2015-04-22
    Description: The effect of aging time on physicochemical and catalytic properties of CuO-ZnO-Al 2 O 3 /HZSM-5 nanocatalyst for direct conversion of syngas to dimethyl ether (DME) has been investigated. Nanocatalysts were synthesized using co-precipitation method in which the aging time varied from 0 to 6 h. The physicochemical properties of the nanocatalysts were studied by X-ray diffraction, Brunauer, Emmett, and Teller, Field Emission Scanning Electron Microscopy (FESEM), energy dispersive X-ray, transmission electron microscopy, FTIR, and temperature-programmed reduction by hydrogen (TPR-H 2 ) techniques. Results showed that the crystallinity of CuO-ZnO-Al 2 O 3 has been increased significantly by increasing of aging time. FESEM analysis showed that, with extension of the aging time, the aggregation of CuO-ZnO-Al 2 O 3 over HZSM-5 has been increased. The size of the particles in the active phase was between 25.0 and 127.1 nm with an average size of 48.36 nm. TPR-H 2 profiles indicated that reducibility of nanocatalysts was enhanced with increasing of aging time. Catalytic performance was investigated at 200–300 °C, 10–40 bar, GHSV = 600 cm 3 g/h, and H 2 /CO = 2. It was found that the increase of aging time had a great influence on the activity of nanocatalysts. Moreover, the 6 h aged nanocatalyst displayed the highest catalytic activity. It was also observed that the optimum operating conditions for syngas to DME reaction were 275 °C and 40 bar.
    Electronic ISSN: 1941-7012
    Topics: Energy, Environment Protection, Nuclear Power Engineering
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  • 23
    Publication Date: 2015-04-22
    Description: The DK4D code has been written to solve a set of time-dependent, axisymmetric, finite-Larmor-radius drift-kinetic equations (DKEs) for the non-Maxwellian part of the electron and ion distribution functions using the full, linearized Fokker–Planck–Landau collision operator. The plasma is assumed to be in the low- to finite-collisionality regime, as is found in the cores of modern and future magnetic confinement fusion experiments. Each DKE is formulated such that the perturbed distribution function carries no net density, parallel momentum, or kinetic energy. Rather, these quantities are contained within the background Maxwellians and would be evolved by an appropriate set of extended magnetohydrodynamic (MHD) equations. This formulation allows for straight-forward coupling of DK4D to existing extended MHD time evolution codes. DK4D uses a mix of implicit and explicit temporal representations and finite element and spectral spatial representations. These, along with other computational methods used, are discussed extensively. Steady-state benchmarks are then presented comparing the results of DK4D to expected analytic results at low collisionality, qualitatively, and to the Sauter analytic fits for the neoclassical conductivity and bootstrap current, quantitatively. These benchmarks confirm that DK4D is capable of solving for the correct, gyroaveraged distribution function in stationary magnetic equilibria. Furthermore, the results presented demonstrate how the exact drift-kinetic solution varies with collisionality as a function of the magnetic moment and the poloidal angle.
    Print ISSN: 1070-664X
    Electronic ISSN: 1089-7674
    Topics: Physics
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  • 24
    Publication Date: 2015-04-22
    Description: Kinetic simulations of two-dimensional finite-amplitude electron plasma waves are performed in a one-wavelength long system. A systematic study of the most unstable linear sideband mode, in particular its growth rate γ and wavenumber k y , is carried out by scanning the amplitude and wavenumber of the initial wave. Simulation results are compared with numerical and analytical solutions to a two-dimensional nonlinear Schrödinger model [H. A. Rose and L. Yin, Phys. Plasmas 15 , 042311 (2008)] and to the reduced model by Kruer et al. [Phys. Rev. Lett. 23 , 838 (1969)] generalized to two dimensions.
    Print ISSN: 1070-664X
    Electronic ISSN: 1089-7674
    Topics: Physics
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  • 25
    Publication Date: 2015-04-22
    Description: The scanning electron microscope is becoming a popular tool to perform tasks that require positioning, manipulation, characterization, and assembly of micro-components. However, some of these applications require a higher level of performance with respect to dynamics and precision of positioning. One limiting factor is the presence of unidentified noises and disturbances. This work aims to study the influence of mechanical disturbances generated by the environment and by the microscope, identifying how these can affect elements in the vacuum chamber. To achieve this objective, a dedicated setup, including a high-resolution vibrometer, was built inside the microscope. This work led to the identification and quantification of main disturbances and noise sources acting on a scanning electron microscope. Furthermore, the effects of external acoustic excitations were analysed. Potential applications of these results include noise compensation and real-time control for high accuracy tasks.
    Print ISSN: 0034-6748
    Electronic ISSN: 1089-7623
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
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  • 26
    Publication Date: 2015-04-22
    Description: A new microelectromechanical systems-based 2-degree-of-freedom (DoF) scanner with an integrated cantilever for on-chip atomic force microscopy (AFM) is presented. The silicon cantilever features a layer of piezoelectric material to facilitate its use for tapping mode AFM and enable simultaneous deflection sensing. Electrostatic actuators and electrothermal sensors are used to accurately position the cantilever within the x-y plane. Experimental testing shows that the cantilever is able to be scanned over a 10 μ m × 10 μ m window and that the cantilever achieves a peak-to-peak deflection greater than 400 nm when excited at its resonance frequency of approximately 62 kHz.
    Print ISSN: 0034-6748
    Electronic ISSN: 1089-7623
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
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  • 27
    Publication Date: 2015-04-22
    Description: Based on our previously developed scheme to stabilize nonplanar optical resonant cavities utilizing polarization caused by a geometric phase in electromagnetic waves traveling along a twisted path, we report an application of the technique for a cavity installed in the Accelerator Test Facility, a 1.3-GeV electron beam accelerator at KEK, in which photons are generated by laser-Compton scattering. We successfully achieved a power enhancement of 1200 with 1.4% fluctuation, which means that the optical path length of the cavity has been controlled with a precision of 14 pm under an accelerator environment. In addition, polarization switching utilizing a geometric phase of the nonplanar cavity was demonstrated.
    Print ISSN: 0034-6748
    Electronic ISSN: 1089-7623
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
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  • 28
    Publication Date: 2015-04-23
    Description: Advances in DNA nanotechnology have stimulated the search for simple motifs that can be used to control the properties of DNA nanostructures. One such motif, which has been used extensively in structures such as polyhedral cages, two-dimensional arrays, and ribbons, is a bulged duplex, that is, two helical segments that connect at a bulge loop. We use a coarse-grained model of DNA to characterize such bulged duplexes. We find that this motif can adopt structures belonging to two main classes: one where the stacking of the helices at the center of the system is preserved, the geometry is roughly straight, and the bulge is on one side of the duplex and the other where the stacking at the center is broken, thus allowing this junction to act as a hinge and increasing flexibility. Small loops favor states where stacking at the center of the duplex is preserved, with loop bases either flipped out or incorporated into the duplex. Duplexes with longer loops show more of a tendency to unstack at the bulge and adopt an open structure. The unstacking probability, however, is highest for loops of intermediate lengths, when the rigidity of single-stranded DNA is significant and the loop resists compression. The properties of this basic structural motif clearly correlate with the structural behavior of certain nano-scale objects, where the enhanced flexibility associated with larger bulges has been used to tune the self-assembly product as well as the detailed geometry of the resulting nanostructures. We further demonstrate the role of bulges in determining the structure of a “Z-tile,” a basic building block for nanostructures.
    Electronic ISSN: 1931-9223
    Topics: Chemistry and Pharmacology , Physics
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  • 29
    Publication Date: 2015-04-23
    Description: Magnetorheological (MR) fluids are suspensions of micron-scale magnetizable particles suspended in a carrier fluid. When field is applied, MR fluids develop a field controllable yield stress and a field independent post-yield viscosity. However, this viscosity has substantial temperature dependence, varying by up to an order of magnitude over the operating temperature range of MR fluid devices. We apply non-Brownian suspension theory to explain this result and find that the majority of this effect should be caused by the temperature dependent behavior of the carrier fluid. Thus, if two fluids share the same carrier fluid, then their fluid properties should scale in temperature similarly. This result is first validated by measuring viscosity across temperature for custom model fluids designed to conform to theory, showing temperature scaling within 5% for both the MR fluids and their carrier fluid. Then, on a series of related commercially available fluids with unknown additive content, we show that the MR fluids exhibit common scaling to within 4%. We also investigate the effects of magnetic hysteresis and find that it induces a negligible increase in yield stress and no measurable change in viscosity. We conclude that our non-dimensional analysis enables the temperature dependence of novel MR fluids to be characterized with fewer experiments.
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
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  • 30
    Publication Date: 2015-04-23
    Description: Thermal relaxation phenomena in mixed-type hysteretic systems are investigated by using recently developed mixed Preisach model and Monte Carlo technique. The anomalous hysteretic behavior observed in several heterogeneous materials, especially in nanoscale embedding, is also generating unconventional relaxation processes which may involve several steps before relaxing to the anhysteretic state. The medium-term relaxation behavior is studied under various noisy environments and applied magnetic fields, analyzing the influence of noise strength, noise bandwidth, and field values on the relaxation characteristics.
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
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  • 31
    Publication Date: 2015-04-23
    Description: This paper proposes, analyzes, and demonstrates a method to characterize fluids by monitoring the rotational dynamics of 2.5- μ m-diameter magnetic microdiscs in suspension via optical interrogation. The free-floating discs function like synchronized micro-shutters when actuated by an external magnetic field. Their motion is monitored via light transmission in response to a rotating magnetic field. The disc rotation is found, both theoretically and experimentally, to depend on the amplitude and the rotation frequency of the applied magnetic field with a high sensitivity to fluid viscosity changes from 1 to 2 mPa s, independent of the disc concentration in the solution from 20 to 120 M/ml. Consequently, the discs can function as microsensors via simple optical measurements.
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
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  • 32
    Publication Date: 2015-04-23
    Description: Brillouin light scattering (BLS) was exploited to study the spin wave properties of spin-valve (SV) type samples basically consisting of two 5 nm-thick NiFe layers (separated by a Cu spacer of 5 nm), differently biased through the interface exchange coupling with an antiferromagnetic IrMn layer. Three samples were investigated: a reference SV sample, without IrMn (reference); one sample with an IrMn underlayer (10 nm thick) coupled to the bottom NiFe film; one sample with IrMn underlayer and overlayer of different thickness (10 nm and 6 nm), coupled to the bottom and top NiFe film, respectively. The exchange coupling with the IrMn, causing the insurgence of the exchange bias effect, allowed the relative orientation of the NiFe magnetization vectors to be controlled by an external magnetic field, as assessed through hysteresis loop measurements by magneto-optic magnetometry. Thus, BLS spectra were acquired by sweeping the magnetic field so as to encompass both the parallel and antiparallel alignment of the NiFe layers. The BLS results, well reproduced by the presented theoretical model, clearly revealed the combined effects on the spin dynamic properties of the dipolar interaction between the two NiFe films and of the interface IrMn/NiFe exchange coupling.
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
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  • 33
    Publication Date: 2015-04-23
    Description: Visualization of the magnetic domain structure is indispensable to the investigation of magnetization processes and the coercivity mechanism. It is necessary to develop a reconstruction method from the reciprocal-space image to the real-space image. For this purpose, it is necessary to solve the problem of missing phase information in the reciprocal-space image. We propose the method of extend Fourier image with mean-value padding to compensate for the phase information. We visualized the magnetic domain structure using the Reverse Monte Carlo method with simulated annealing to accelerate the calculation. With this technique, we demonstrated the restoration of the magnetic domain structure, obtained magnetization and magnetic domain width, and reproduced the characteristic form that constitutes a magnetic domain.
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
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  • 34
    Publication Date: 2015-04-23
    Description: A tetragonally distorted FeCo structure is obtained in Fe/Co multilayers epitaxially grown on Au 50 Cu 50 buffer using MgO single crystal substrates as a result of the lattice mismatch between the buffer and the FeCo ferromagnetic layer. The presence of large magnetic anisotropy energy (MAE) of the order of 1 MJ/m 3 has been confirmed by ferromagnetic resonance. Furthermore, the effect of carbon (C) doping to maintain the tetragonal distortion throughout the thickness of 3 nm FeCo has been investigated. Our study shows that FeCo alloys maintain large magnetic moment and possess high MAE properties that are required for designing permanent magnets.
    Electronic ISSN: 2166-532X
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 35
    Publication Date: 2015-04-23
    Description: Interface engineering of structural distortions is a key for exploring the functional properties of oxide heterostructures and superlattices. In this paper, we report on our comprehensive investigations of oxygen octahedral distortions at the heterointerface between perovskite oxides SrRuO 3 and BaTiO 3 on GdScO 3 substrates and of the influences of the interfacially engineered distortions on the magneto-transport properties of the SrRuO 3 layer. Our state-of-the-art annular bright-field imaging in aberration-corrected scanning transmission electron microscopy revealed that the RuO 6 octahedral distortions in the SrRuO 3 layer have strong dependence on the stacking order of the SrRuO 3 and BaTiO 3 layers on the substrate. This can be attributed to the difference in the interfacial octahedral connections. We also found that the stacking order of the oxide layers has a strong impact on the magneto-transport properties, allowing for control of the magnetic anisotropy of the SrRuO 3 layer through interface engineering. Our results demonstrate the significance of the interface engineering of the octahedral distortions on the structural and physical properties of perovskite oxides.
    Electronic ISSN: 2166-532X
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 36
    Publication Date: 2015-04-23
    Description: To realize multiferroic and magnetoelectric properties, bi-layered nanocomposite films consisting of CoFe 2 O 4 (CFO)/Pb 1−x Sr x TiO 3 (PST) phases (x = 0.1, 0.2, and 0.3) have been deposited on Pt/TiO 2 /SiO 2 /Si substrate by using a metallo-organic decomposition process. Both the PST perovskite and the CFO spinel phases are confirmed from X-ray diffraction patterns and Raman spectra of the composite films. The composite films exhibit room temperature multiferroic properties. The values of saturation magnetization ( M s ), remanent magnetization ( M r ), and coercive field ( H c ) of the composite films are in the range of 108–119 kA/m, 42–51 kA/m, and 44.5–64.1 kA/m, respectively. In addition, the saturation polarization ( P s ), remanent polarization ( P r ), and electrical coercive field ( E c ) are observed in the range of 11.3–14.4  μ C/cm 2 , 2.9–4.8  μ C/cm 2 , and 56–59.5 kV/cm, respectively. The dielectric response in the presence of applied magnetic field, H dc  ∼ 238.6 kA/m shows a high magnetocapacitance value ∼385% at frequency 100 kHz for CFO/PST composite film with x = 0.1. The maximum magnetoelectric voltage co-efficient value, α E  ∼ 380 kV/(m × T) has been achieved in the composite films with x = 0.1. The influence of elastic/and or interfacial strain on multiferroic magnetoelectric properties is evident from the results.
    Print ISSN: 0021-8979
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  • 37
    Publication Date: 2015-04-23
    Description: The magnetic and electrical properties in phase-separated La 0.7 Ca 0.3 Mn 0.9 Cu 0.1 O 3 perovskite were studied in detail. Experimental results show that the substitution of Cu at Mn-site suppresses the ferromagnetic (FM) phase of La 0.7 Ca 0.3 MnO 3 matrix and induces a charge ordering transition at ∼146 K. At ∼256 K, a Griffiths-like behaviour is observed. At low temperatures, the occurrence of an irreversible metamagnetic transition associated with a large relaxation rate is analyzed, clearly indicating the dynamic phase coexistence and evolution of FM islands. A magnetic phase diagram is finally constructed based on the magnetic measurements, summarizing the dynamic evolution process of phase separation.
    Print ISSN: 0021-8979
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  • 38
    Publication Date: 2015-04-23
    Description: Measurements of the adiabatic temperature change (ΔT) and the specific heat transfer (ΔQ) of Ni 2.18 Mn 0.82 Ga Heusler alloy were taken in order to quantify the direct giant magnetocaloric effect of the alloy when it is in the vicinity of magneto-structural phase transition (PT) from paramagnetic austenite to ferromagnetic martensite, and their results are presented. A new vacuum calorimeter was used to simultaneously measure ΔT and ΔQ of magnetocaloric materials with a Bitter coil magnet in fields of up to H = 140 kOe. Other thermomagnetic properties of this alloy were investigated using standard differential scanning calorimetry and PPMS equipment. The maximal values of magnetocaloric effect in H = 140 kOe were found to be ΔT = 8.4 K at initial temperature 340 K and ΔQ = 4900 J/kg at 343 K. Using this direct method, we show that the alloy indeed demonstrates the largest value of ΔQ as compared with previously published results for direct measurements of magnetocaloric materials, even though at 140 kOe the magnetic field-induced magnetostructural PT is still not complete.
    Print ISSN: 0021-8979
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  • 39
    Publication Date: 2015-04-23
    Description: The isoeletronic diatomic MoC − and NbN − anions have been prepared by laser ablation and studied by photoelectron imaging spectroscopy combined with quantum chemistry calculations. The photoelectron spectra of NbN − can be very well assigned on the basis of literature reported optical spectroscopy of NbN. In contrast, the photoelectron spectra of MoC − are rather complex and the assignments suffered from the presence of many electronically hot bands and limited information from the reported optical spectroscopy of MoC. The electron affinities of NbN and MoC have been determined to be 1.450 ± 0.003 eV and 1.360  ±  0.003 eV, respectively. The good resolution of the imaging spectroscopy provided a chance to resolve the Ω splittings of the X 3 Σ − (Ω = 0 and 1) state of MoC and the X 4 Σ − (Ω = 1/2 and 3/2) state of MoC − for the first time. The spin-orbit splittings of the X 2 Δ state of NbN − and the a 2 Δ state of MoC − were also determined. The similarities and differences between the electronic structures of the NbN and MoC systems were discussed.
    Print ISSN: 0021-9606
    Electronic ISSN: 1089-7690
    Topics: Chemistry and Pharmacology , Physics
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  • 40
    Publication Date: 2015-04-23
    Description: Because it is sensitive to fluctuations occurring over femtoseconds to picoseconds, gigahertz-to-terahertz dielectric relaxation spectroscopy can provide a valuable window into water’s most rapid intermolecular motions. In response, we have built a vector network analyzer dielectric spectrometer capable of measuring absorbance and index of refraction in this frequency regime with unprecedented precision. Using this to determine the complex dielectric response of water and aqueous salt solutions from 5.9 GHz to 1.12 THz (which we provide in the supplementary material), we have obtained strong new constraints on theories of water’s collective dynamics. For example, while the salt-dependencies we observe for water’s two slower relaxations (8 and 1 ps) are easily reconciled with suggestions that they arise due to rotations of fully and partially hydrogen bonded molecules, respectively, the salt-dependence of the fastest relaxation (180 fs) appears difficult to reconcile with its prior assignment to liberations of single hydrogen bonds.
    Print ISSN: 0021-9606
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    Topics: Chemistry and Pharmacology , Physics
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  • 41
    Publication Date: 2015-04-23
    Description: The typical ionic liquid, 1-ethyl-3-methyl imidazolium nitrate (EMIM-NO 3 ), was examined by molecular dynamics simulations of an all-atomistic model to show the characteristics of networks of cages and/or bonds in the course of vitrification of this fragile glass-former. The system shows changes of dynamics at two characteristic temperatures, T B (or T c ) and the glass transition temperature T g , found in other fragile glass forming liquids [K. L. Ngai and J. Habasaki, J. Chem. Phys. 141 , 114502 (2014)]. On decreasing temperature, the number of neighboring cation-anion pairs, N B , within the first minimum of the pair correlation function, g ( r ) min , increases. On crossing T B (〉 T g ), the system volume and diffusion coefficient both show changes in temperature dependence, and as usual at T g . The glass transition temperature, T g , is characterized by the saturation of the total number of “bonds,” N B and the corresponding decrease in degree of freedom, F = [(3 N − 6) − N B ], of the system consisting of N particles. Similar behavior holds for the other ion-ion pairs. Therefore, as an alternative, the dynamics of glass transition can be interpreted conceptually by rigidity percolation. Before saturation occurring at T g , the number of bonds shows a remarkable change at around T B . This temperature is associated with the disappearance of the loosely packed coordination polyhedra of anions around cation (or vice versa), related to the loss of geometrical freedom of the polyhedra, f g , of each coordination polyhedron, which can be defined by f g = [(3 N V − 6) − N b ]. Here, 3 N v is the degree of freedom of N V vertices of the polyhedron, and N b is number of fictive bonds. The packing of polyhedra is characterized by the soft percolation of cages, which allows further changes with decreasing temperature. The power spectrum of displacement of the central ion in the cage is found to be correlated with the fluctuation of N b of cation-cation (or anion-anion) pairs in the polyhedron, although the effect from the coordination shells beyond the neighboring ions is not negligible.
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  • 42
    Publication Date: 2015-04-23
    Description: Advances in DNA nanotechnology have stimulated the search for simple motifs that can be used to control the properties of DNA nanostructures. One such motif, which has been used extensively in structures such as polyhedral cages, two-dimensional arrays, and ribbons, is a bulged duplex, that is, two helical segments that connect at a bulge loop. We use a coarse-grained model of DNA to characterize such bulged duplexes. We find that this motif can adopt structures belonging to two main classes: one where the stacking of the helices at the center of the system is preserved, the geometry is roughly straight, and the bulge is on one side of the duplex and the other where the stacking at the center is broken, thus allowing this junction to act as a hinge and increasing flexibility. Small loops favor states where stacking at the center of the duplex is preserved, with loop bases either flipped out or incorporated into the duplex. Duplexes with longer loops show more of a tendency to unstack at the bulge and adopt an open structure. The unstacking probability, however, is highest for loops of intermediate lengths, when the rigidity of single-stranded DNA is significant and the loop resists compression. The properties of this basic structural motif clearly correlate with the structural behavior of certain nano-scale objects, where the enhanced flexibility associated with larger bulges has been used to tune the self-assembly product as well as the detailed geometry of the resulting nanostructures. We further demonstrate the role of bulges in determining the structure of a “Z-tile,” a basic building block for nanostructures.
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  • 43
    Publication Date: 2015-04-23
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  • 44
    Publication Date: 2015-04-23
    Description: The electronic efficiency and binding energy of contacts formed between graphene electrodes and poly-aromatic hydrocarbon (PAH) anchoring groups have been investigated by the non-equilibrium Green’s function formalism combined with density functional theory. Our calculations show that PAH molecules always bind in the interior and at the edge of graphene in the AB stacking manner, and that the binding energy increases following the increase of the number of carbon and hydrogen atoms constituting the PAH molecule. When we move to analyzing the electronic transport properties of molecular junctions with a six-carbon alkyne chain as the central molecule, the electronic efficiency of the graphene-PAH contacts is found to depend on the energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of the corresponding PAH anchoring group, rather than its size. To be specific, the smaller is the HOMO-LUMO gap of the PAH anchoring group, the higher is the electronic efficiency of the graphene-PAH contact. Although the HOMO-LUMO gap of a PAH molecule depends on its specific configuration, PAH molecules with similar atomic structures show a decreasing trend for their HOMO-LUMO gap as the number of fused benzene rings increases. Therefore, graphene-conjugated molecule-graphene junctions with high-binding and high-conducting graphene-PAH contacts can be realized by choosing appropriate PAH anchor groups with a large area and a small HOMO-LUMO gap.
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  • 45
    Publication Date: 2015-04-23
    Description: The photoluminescence (PL) of a novel imide-substituted poly(3-thienylenevinylene) derivative (imidePTV) was studied in film and solution. PL quantum efficiency was measured to be more than two orders of magnitude larger than its nonluminescent counterpart, namely, alkyl-substituted PTV and was interpreted as evidence for a near degeneracy of optically allowed 1 1 B u and optically forbidden 2 1 A g excitonic states. As a result, coexistence of 2 1 A g and 1 1 B u emissions was observed, and the predominance was found to be sensitive to temperature and morphological environment. PL of solutions in solvents of higher polarity and polarizability and from low-temperature films was dominated by the transition from the dipole allowed 1 1 B u state. On the other hand, the PL spectra of films at high temperature and solutions in solvents of low polarity and polarizability were primarily from the 2 1 A g state that obtains a finite transmission moment from an asymmetric perturbation mixing with the 1 1 B u .
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  • 46
    facet.materialart.
    facet.materialart.
    American Institute of Physics (AIP)
    Publication Date: 2015-04-23
    Description: Existence of a complex structure on the 6 dimensional sphere is proved in this paper. The proof is based on re-interpreting a hypothetical complex structure as a classical ground state of a Yang–Mills–Higgs-like theory on S 6 . This classical vacuum solution is then constructed by Fourier expansion (dimensional reduction) from the obvious one of a similar theory on the 14 dimensional exceptional compact Lie group G 2 .
    Print ISSN: 0022-2488
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  • 47
    Publication Date: 2015-04-23
    Description: The superintegrability of four Hamiltonians H r ˜ = λ   H r , r = a , b , c , d , where H r are known Hamiltonians and λ is a certain function defined on the configuration space and depended on a parameter κ , is studied. The new Hamiltonians, and the associated constants of motion J ri , i = 1, 2, 3, are continous functions of the parameter κ . The first part is concerned with separability and quadratic superintegrability (the integrals of motion are quadratic in the momenta) and the second part is devoted to the existence of higher-order superintegrability. The results obtained in the second part are related with the Tremblay-Turbiner-Winternitz and the Post–Winternitz systems.
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  • 48
    Publication Date: 2015-04-24
    Description: Estimating the relative stabilities of different conformational states of a (bio-)molecule using molecular dynamics simulations involves two challenging problems: the conceptual problem of how to define the states of interest and the technical problem of how to properly sample these states, along with achieving a sufficient number of interconversion transitions. In this study, the two issues are addressed in the context of a decaalanine peptide in water, by considering the 3 10 -, α -, and π -helical states. The simulations rely on the ball-and-stick local-elevation umbrella-sampling (B&S-LEUS) method. In this scheme, the states are defined as hyperspheres (balls) in a (possibly high dimensional) collective-coordinate space and connected by hypercylinders (sticks) to ensure transitions. A new object, the pipe, is also introduced here to handle curvilinear pathways. Optimal sampling within the so-defined space is ensured by confinement and (one-dimensional) memory-based biasing potentials associated with the three different kinds of objects. The simulation results are then analysed in terms of free energies using reweighting, possibly relying on two distinct sets of collective coordinates for the state definition and analysis. The four possible choices considered for these sets are Cartesian coordinates, hydrogen-bond distances, backbone dihedral angles, or pairwise sums of successive backbone dihedral angles. The results concerning decaalanine underline that the concept of conformational state may be extremely ambiguous, and that its tentative absolute definition as a free-energy basin remains subordinated to the choice of a specific analysis space. For example, within the force-field employed and depending on the analysis coordinates selected, the 3 10 -helical state may refer to weakly overlapping collections of conformations, differing by as much as 25 kJ mol −1 in terms of free energy. As another example, the π -helical state appears to correspond to a free-energy basin for three choices of analysis coordinates, but to be unstable with the fourth one. The problem of conformational-state definition may become even more intricate when comparison with experiment is involved, where the state definition relies on spectroscopic or functional observables.
    Electronic ISSN: 1931-9223
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  • 49
    Publication Date: 2015-04-24
    Description: Transmission line techniques are a convenient way to determine the electromagnetic properties of a variety of materials in the ranges of radio and microwave frequencies. Traditional methods based on the measurement of the four scattering parameters can be successfully replaced for the method presented here, in which no change in the geometry is needed, since two independent measurements are carried out, with and without an applied magnetic field. In addition, given the small size of the sample holder, the required amount of material can be drastically reduced, and allow the use of a lumped circuit model, then reducing the inherent difficulties associated with the use of distributed parameters. Even though this kind of model requires the involved wavelengths to be much larger than the size of the system, this requirement can be overcome as long as the tested materials have relative ϵ or μ lower than 100. Furthermore, the use of short-circuited transmission lines simplifies sample holding and systematizes the measurement process, which is an important target when dealing with measurements within the radio and microwave frequency ranges.
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  • 50
    Publication Date: 2015-04-24
    Description: Power transfer capability of wireless power transfer systems is highly dependent on the magnetic design of the primary and secondary inductors and is measured quantitatively by the coupling factor. The inductors are designed by placing the coil over a ferrite base to increase the coupling factor and reduce magnetic emissions to the surroundings. Effect of adding extra ferrite above the base ferrite at different physical locations on the self-inductance, mutual inductance, and coupling factor is under investigation in this paper. The addition can increase or decrease the mutual inductance depending on the placement of ferrite. Also, the addition of ferrite increases the self-inductance of the coils, and there is a probability for an overall decrease in the coupling factor. Correct placement of ferrite, on the other hand, can increase the coupling factor relatively higher than the base ferrite as it is closer to the other inductor. Ferrite being a heavy compound of iron increases the inductor weight significantly and needs to be added judiciously. Four zones have been identified in the paper, which shows different sensitivity to addition of ferrite in terms of the two inductances and coupling factor. Simulation and measurement results are presented for different air gaps between the coils and at different gap distances between the ferrite base and added ferrite. This paper is beneficial in improving the coupling factor while adding minimum weight to wireless power transfer system.
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  • 51
    Publication Date: 2015-04-24
    Description: In this study, FeMn was introduced as an antiferromagnetic (AFM) layer to couple with a single-layered Co 49 Pt 51 alloy thin film, and it was compared with a Co 49 Pt 51 /IrMn bilayer system in exchange bias (EB) effect, to explore the mechanism of spontaneous perpendicular exchange bias (PEB), which has been recently observed in CoPt/IrMn bilayers. Bilayers of CoPt/IrMn and CoPt/FeMn were prepared under the same conditions by sputtering at room temperature without any inducing field. Although PEB was observed in as-grown CoPt/FeMn bilayers, the loop shape and PEB behavior were found to exhibit different characteristics from those of CoPt/IrMn bilayers. The CoPt (5 nm)/FeMn (10 nm) bilayer has a sheared loop that is similar to a double-shifted loop and a much lower squareness ratio (SQR = 0.52) and exchange bias field ( H e  = 180 Oe) than the CoPt (5 nm)/IrMn (10 nm) system, which has a rectangular loop shape and a high SQR of 0.97 and large H e of 290 Oe. The two systems present entirely different dependences of PEB on the thickness of the AFM layer. CoPt/IrMn exhibits behavior that is typical of most EB systems, but for CoPt/FeMn, this dependence is more complicated with an unusual peak at an AFM layer thickness of 10 nm. Based on the dissimilar loop shapes and dependences of PEB on AFM thickness, the mechanisms of the spontaneously established PEB in these two systems are considered to differ. Investigations of cross-sectional transmission electron microscopy revealed no apparent difference between the interfacial microstructures of the two systems. X-ray diffraction studies demonstrated the ⟨111⟩ texture of both systems. Therefore, different interfacial spin configurations may be responsible for the dissimilar PEB behaviors in these two FM/AFM bilayer systems.
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  • 52
    Publication Date: 2015-04-24
    Description: Effect of bcc Cr 80 Mn 20 seed layer and Cr 50 Ti 50 amorphous texture inducing layer on the heteroepitaxy system in FePt-C granular film was studied by introducing a new concept of the layered structure. The concept suggested that the large grain seed layer in which the crystallographic texture was initially formed on an amorphous layer in the layered structure can reduce the angular distribution of (002) c -axis crystal orientation in the FePt-C granular film owing to heteroepitaxial growth. Structure analysis by X-ray diffraction revealed that (1) when the substrate heating temperature was elevated from 300 °C to 500 °C, grain size in the seed layer increased from 9.8 nm to 11.6 nm, and then decreased with further increasing the substrate temperature. The reduction of the grain size over 500 °C corresponds to the crystallization of the amorphous texture inducing layer, (2) when the grain size increased from 9.8 nm to 11.6 nm, the angular distribution of the (002) orientation in the seed layer dramatically decreased from 13.7° to 4.1°. It was shown that the large grain seed layer increased the perpendicular hysteresis in FePt-C granular film.
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  • 53
    Publication Date: 2015-04-24
    Description: We successfully fabricate a (100)-orientated B 2-type-Co 2 FeSi 0.5 Al 0.5 (CFSA)/MgO/Si(100) tunnel contact that is promising for an efficient spin injector for Si channels. The MgO barrier is formed by radical oxidation of an Mg thin film deposited on a Si(100) surface at room temperature and successive radical oxygen annealing at 400 °C. The CFSA electrode is grown on the MgO barrier at 400 °C by ultrahigh-vacuum molecular beam deposition, and it exhibits a (100)-orientated columnar polycrystalline structure with a high degree (63%) of B 2-order. The MgO barrier near the interface of the CFSA/MgO junction is crystallized with the (100) orientation, i.e., the spin filter effect due to the MgO barrier could be expected for this junction. A three-terminal Si-channel spin-accumulation device with a CFSA/MgO/Si(100) spin injector is fabricated, and the Hanle effect of accumulated spin polarized electrons injected from this contact to the Si channel is observed.
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  • 54
    Publication Date: 2015-04-24
    Description: An atomic layer stacking structure in hexagonal close packed (hcp) Co 100− x Pt x alloy films with c -plane sheet texture was directly observed by a high-angle annular dark-field imaging scanning transmission electron microscopy. The analysis of sequential and/or compositional atomic layer stacking structure and uniaxial magnetocrystalline anisotropy ( K u  =  K u1  +  K u2 ) revealed that (1) integrated intensity of the superlattice diffraction takes the maximum at x  = 20 at. % and shows broadening feature against x for the film fabricated under the substrate temperature ( T sub ) of 400 °C. (2) Compositional separation structure in atomic layers is formed for the films fabricated under T sub  = 400 °C. A sequential alternative stacking of atomic layers with different compositions is hardly formed in the film with x  = 50 at. %, whereas easily formed in the film with x  = 20 at. %. This peculiar atomic layer stacking structure consists of in-plane-disordered Pt-rich and Pt-poor layers, which is completely different from the so-called atomic site ordered structure. (3) A face centered cubic atomic layer stacking as faults appeared in the host hcp atomic layer stacking exists in accompanies with irregularities for the periodicity of the compositional modulation atomic layers. (4) K u1 takes the maximum of 1.4 × 10 7  erg/cm 3 at around x  = 20 at. %, whereas K u2 takes the maximum of 0.7 × 10 7  erg/cm 3 at around x  = 40 at. %, which results in the maximum of 1.8 × 10 7  erg/cm 3 of K u at x  = 30 at. % and a shoulder in compositional dependence of K u in the range of x  = 30–60 at. %. Not only compositional separation of atomic layers but also sequential alternative stacking of different compositional layers is quite important to improve essential uniaxial magnetocrystalline anisotropy.
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  • 55
    Publication Date: 2015-04-24
    Description: The magneto-static behaviour of soft magnetic composites (SMCs) is investigated using tomography based direct numerical simulation. The microgeometry crucially affects the magnetic properties of the composite since a geometry dependent demagnetizing field is established inside the composite, which lowers the magnetic permeability. We determine the magnetic field information inside the SMC using direct numerical simulation of the magnetic field based on high resolution micro-computed tomography data of the SMC's microstructure as well as artificially generated data made of statistically homogeneous systems of identical fully penetrable spheres and prolate spheroids. Quasi-static electromagnetic behaviour and linear material response are assumed. The 3D magnetostatic Maxwell equations are solved using Whitney finite elements. Simulations show that clustering and percolation behaviour determine the demagnetizing factor of SMCs rather than the particle shape. The demagnetizing factor correlates with the slope of a 2-point probability function at its origin, which is related to the specific surface area of the SMC. Comparison with experimental results indicates that the relatively low permeability of SMCs cannot be explained by demagnetizing effects alone and suggests that the permeability of SMC particles has to be orders of magnitude smaller than the bulk permeability of the particle material.
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  • 56
    Publication Date: 2015-04-24
    Description: Ensuring a permanent increase of magnetic storage densities is one of the main challenges in magnetic recording. Conventional approaches based on single phase grains are not suitable to achieve this goal, because their grain volume is limited due to the superparamagnetic limit. Grains with graded anisotropy are the most promising candidates to overcome this limit, providing magnetic memory bits with small volumes, low coercivity, and high thermal stability at the same time. Combining micromagnetic simulations with forward flux sampling, a computational method for rare events that has been recently applied to the magnetic nanostructures, we have determined thermal escape rates and attempt frequencies of a graded media grain and two single phase grains of the same geometry. We find that graded anisotropy can increase the thermal stability of a grain by 12 orders of magnitudes from tens of milliseconds to centuries without changing the coercive field.
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  • 57
    Publication Date: 2015-04-24
    Description: We consider a thermally stable, metallic nanoscale ferromagnet (FM) subject to spin-polarized current injection and exchange coupling from the spin-helically locked surface states of a topological insulator (TI) to evaluate possible non-volatile memory applications. We consider parallel transport in the TI and the metallic FM, and focus on the efficiency of magnetization switching as a function of transport between the TI and the FM. Transport is modeled as diffusive in the TI beneath the FM, consistent with the mobility in the TI at room temperature, and in the FM, which essentially serves as a constant potential region albeit spin-dependent except in the low conductivity, diffusive limit. Thus, it can be captured by drift-diffusion simulation, which allows for ready interpretation of the results. We calculate switching time and energy consumed per write operation using self-consistent transport, spin-transfer-torque (STT), and magnetization dynamics calculations. Calculated switching energies and times compare favorably to conventional spin-torque memory schemes for substantial interlayer conductivity. Nevertheless, we find that shunting of current from the TI to a metallic nanomagnet can substantially limit efficiency. Exacerbating the problem, STT from the TI effectively increases the TI resistivity. We show that for optimum performance, the sheet resistivity of the FM layer should be comparable to or larger than that of the TI surface layer. Thus, the effective conductivity of the FM layer becomes a critical design consideration for TI-based non-volatile memory.
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  • 58
    Publication Date: 2015-04-24
    Description: Estimating the relative stabilities of different conformational states of a (bio-)molecule using molecular dynamics simulations involves two challenging problems: the conceptual problem of how to define the states of interest and the technical problem of how to properly sample these states, along with achieving a sufficient number of interconversion transitions. In this study, the two issues are addressed in the context of a decaalanine peptide in water, by considering the 3 10 -, α -, and π -helical states. The simulations rely on the ball-and-stick local-elevation umbrella-sampling (B&S-LEUS) method. In this scheme, the states are defined as hyperspheres (balls) in a (possibly high dimensional) collective-coordinate space and connected by hypercylinders (sticks) to ensure transitions. A new object, the pipe, is also introduced here to handle curvilinear pathways. Optimal sampling within the so-defined space is ensured by confinement and (one-dimensional) memory-based biasing potentials associated with the three different kinds of objects. The simulation results are then analysed in terms of free energies using reweighting, possibly relying on two distinct sets of collective coordinates for the state definition and analysis. The four possible choices considered for these sets are Cartesian coordinates, hydrogen-bond distances, backbone dihedral angles, or pairwise sums of successive backbone dihedral angles. The results concerning decaalanine underline that the concept of conformational state may be extremely ambiguous, and that its tentative absolute definition as a free-energy basin remains subordinated to the choice of a specific analysis space. For example, within the force-field employed and depending on the analysis coordinates selected, the 3 10 -helical state may refer to weakly overlapping collections of conformations, differing by as much as 25 kJ mol −1 in terms of free energy. As another example, the π -helical state appears to correspond to a free-energy basin for three choices of analysis coordinates, but to be unstable with the fourth one. The problem of conformational-state definition may become even more intricate when comparison with experiment is involved, where the state definition relies on spectroscopic or functional observables.
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  • 59
    Publication Date: 2015-04-24
    Description: Pressure, density, and temperature data for H 2 O were obtained up to 260 GPa by using laser-driven shock compression technique. The shock compression technique combined with the diamond anvil cell was used to assess the equation of state models for the P - ρ - T conditions for both the principal Hugoniot and the off-Hugoniot states. The contrast between the models allowed for a clear assessment of the equation of state models. Our P - ρ - T data totally agree with those of the model based on quantum molecular dynamics calculations. These facts indicate that this model is adopted as the standard for modeling interior structures of Neptune, Uranus, and exoplanets in the liquid phase in the multi-Mbar range.
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  • 60
    Publication Date: 2015-04-24
    Description: We investigate microscopic structure and thermodynamic properties of a mixture that contains amphiphilic molecules and charged hard spheres confined in slit-like pores with uncharged hard walls. The model and the density functional approach are the same as described in details in our previous work [Pizio et al. , J. Chem. Phys. 140 , 174706 (2014)]. Our principal focus is in exploring the effects brought by the presence of ions on the structure of confined amphiphilic particles. We have found that for some cases of anisotropic interactions, the change of the structure of confined fluids occurs via the first-order transitions. Moreover, if anions and cations are attracted by different hemispheres of amphiphiles, a charge at the walls appears at the zero value of the wall electrostatic potential. For a given thermodynamic state, this charge is an oscillating function of the pore width.
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  • 61
    Publication Date: 2015-04-24
    Description: An algorithm to compute Connes spectral distance, adaptable to the Hilbert-Schmidt operatorial formulation of non-commutative quantum mechanics, was developed earlier by introducing the appropriate spectral triple and used to compute infinitesimal distances in the Moyal plane, revealing a deep connection between geometry and statistics. In this paper, using the same algorithm, the Connes spectral distance has been calculated in the Hilbert-Schmidt operatorial formulation for the fuzzy sphere whose spatial coordinates satisfy the su (2) algebra. This has been computed for both the discrete and the Perelemov’s SU (2) coherent state. Here also, we get a connection between geometry and statistics which is shown by computing the infinitesimal distance between mixed states on the quantum Hilbert space of a particular fuzzy sphere, indexed by n ∈ ℤ/2.
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  • 62
    Publication Date: 2015-04-24
    Description: An analytical theory is developed for studying the phenomenon of generation of harmonics by the propagation of an obliquely incident, circularly polarized laser beam in homogeneous, underdense plasma. The amplitudes of second and third harmonic radiation as well as detuning distance have been obtained and their variation with the angle of incidence is analyzed. The amplitude of harmonic radiation increases with the angle of incidence while the detuning distance decreases, for a given plasma electron density. It is observed that the generated second and third harmonic radiation is linearly and elliptically polarized, respectively. The harmonic radiation vanishes at normal incidence of the circularly polarized laser beam.
    Print ISSN: 1070-664X
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  • 63
    Publication Date: 2015-04-24
    Description: We create streaming ultracold neutral plasmas by tailoring the photoionizing laser beam that creates the plasma. By varying the electron temperature, we control the relative velocity of the streaming populations, and, in conjunction with variation of the plasma density, this controls the ion collisionality of the colliding streams. Laser-induced fluorescence is used to map the spatially resolved density and velocity distribution function for the ions. We identify the lack of local thermal equilibrium and distinct populations of interpenetrating, counter-streaming ions as signatures of kinetic behavior. Experimental data are compared with results from a one-dimensional, two-fluid numerical simulation.
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  • 64
    facet.materialart.
    facet.materialart.
    American Institute of Physics (AIP)
    Publication Date: 2015-04-24
    Description: A model-based robust control approach is proposed that significantly improves imaging bandwidth for the dynamic mode atomic force microscopy. A model for cantilever oscillation amplitude and phase dynamics is derived and used for the control design. In particular, the control design is based on a linearized model and robust H ∞ control theory. This design yields a significant improvement when compared to the conventional proportional-integral designs and verified by experiments.
    Print ISSN: 0034-6748
    Electronic ISSN: 1089-7623
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  • 65
    Publication Date: 2015-04-24
    Description: A novel monolithic piezoelectric actuated wire clamp is presented in this paper to achieve fast, accurate, and robust microelectronic device packaging. The wire clamp has compact, flexure-based mechanical structure and light weight. To obtain large and robust jaw displacements and ensure parallel jaw grasping, a two-stage amplification composed of a homothetic bridge type mechanism and a parallelogram leverage mechanism was designed. Pseudo-rigid-body model and Lagrange approaches were employed to conduct the kinematic, static, and dynamic modeling of the wire clamp and optimization design was carried out. The displacement amplification ratio, maximum allowable stress, and natural frequency were calculated. Finite element analysis (FEA) was conducted to evaluate the characteristics of the wire clamp and wire electro discharge machining technique was utilized to fabricate the monolithic structure. Experimental tests were carried out to investigate the performance and the experimental results match well with the theoretical calculation and FEA. The amplification ratio of the clamp is 20.96 and the working mode frequency is 895 Hz. Step response test shows that the wire clamp has fast response and high accuracy and the motion resolution is 0.2 μm. High speed precision grasping operations of gold and copper wires were realized using the wire clamper.
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  • 66
    Publication Date: 2015-04-24
    Description: Compared with conventional DGA (dissolved gas analysis) method for on-line monitoring of power transformers, FBG (fiber Bragg grating) hydrogen sensor represents marked advantages over immunity to electromagnetic field, time-saving, and convenience to defect location. Thus, a novel FBG hydrogen sensor based on Pd/Ag (Palladium/Silver) along with polyimide composite film to measure dissolved hydrogen concentration in large power transformers is proposed in this article. With the help of Pd/Ag composite coating, the enhanced performance on mechanical strength and sensitivity is demonstrated, moreover, the response time and sensitivity influenced by oil temperature are solved by correction lines. Sensitivity measurement and temperature calibration of the specific hydrogen sensor have been done respectively in the lab. And experiment results show a high sensitivity of 0.055 pm/( μ l/l) with instant response time about 0.4 h under the typical operating temperature of power transformers, which proves a potential utilization inside power transformers to monitor the health status by detecting the dissolved hydrogen concentration.
    Print ISSN: 0034-6748
    Electronic ISSN: 1089-7623
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
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  • 67
    Publication Date: 2015-04-24
    Description: We have developed a practical method for determining an excellent initial arrangement of magnetic arrays for a pure-magnet Halbach-type undulator. In this method, the longitudinal magnetic field distribution of each magnet is measured using a moving Hall probe system along the beam axis with a high positional resolution. The initial arrangement of magnetic arrays is optimized and selected by analyzing the superposition of all distribution data in order to achieve adequate spectral quality for the undulator. We applied this method to two elliptically polarizing undulators (EPUs), called U#16-2 and U#02-2, at the Photon Factory storage ring (PF ring) in the High Energy Accelerator Research Organization (KEK). The measured field distribution of the undulator was demonstrated to be excellent for the initial arrangement of the magnet array, and this method saved a great deal of effort in adjusting the magnetic fields of EPUs.
    Print ISSN: 0034-6748
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    Topics: Electrical Engineering, Measurement and Control Technology , Physics
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  • 68
    Publication Date: 2015-04-25
    Description: We investigate the suitability of an epitaxial CaTiO 3 buffer layer deposited onto (100) Si by reactive molecular-beam epitaxy (MBE) for the epitaxial integration of the colossal magnetoresistive material La 0.7 Sr 0.3 MnO 3 with silicon. The magnetic and electrical properties of La 0.7 Sr 0.3 MnO 3 films deposited by MBE on CaTiO 3 -buffered silicon (CaTiO 3 /Si) are compared with those deposited on SrTiO 3 -buffered silicon (SrTiO 3 /Si). In addition to possessing a higher Curie temperature and a higher metal-to-insulator transition temperature, the electrical resistivity and 1/ f noise level at 300 K are reduced by a factor of two in the heterostructure with the CaTiO 3 buffer layer. These results are relevant to device applications of La 0.7 Sr 0.3 MnO 3 thin films on silicon substrates.
    Electronic ISSN: 2166-532X
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 69
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    American Institute of Physics (AIP)
    Publication Date: 2015-04-25
    Description: We report on the advance of chip-scale cavity optomechanical resonators to beyond 10 GHz by exploiting the fundamental acoustic thickness mode of an aluminum nitride micro-disk. By engineering the mechanical anchor to minimize the acoustic loss, a quality factor of 1830 and hence a frequency-quality factor product of 1.9 × 10 13  Hz are achieved in ambient air at room temperature. Actuated by strong piezo-electric force, the micro-disk resonator shows an excellent electro-optomechanical transduction efficiency. Our detailed analysis of the electro-optomechanical coupling allows identification and full quantification of various acoustic modes spanning from super-high to X-band microwave frequencies measured in the thin film resonator.
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
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  • 70
  • 71
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    facet.materialart.
    American Institute of Physics (AIP)
    Publication Date: 2015-04-25
    Description: Magnetocardiography (MCG) of healthy volunteers has been measured by using a fundamental mode orthogonal fluxgate magnetometer array of 32 channels in a magnetic shielded room (MSR). Sensor heads, which are employed, consist of a 45 mm long U-shaped amorphous wire core and a 1000-turn solenoid pick-up coil of 30 mm in length and 3 mm in outer diameter. The excitation current of 100 kHz with large dc bias current is fed directly into wire cores, which are connected in series, whereas the signal detection circuit is provided to each of the sensor heads. A special technique to avoid mutual interaction between sensor heads is implemented, where all the sensor heads are excited synchronously by using a single ac source. A 2-D array having 32 sensors with 4 cm grid spacing was used to measure MCG signals inside an MSR. Measured data from each channel were first filtered (0.16–100 Hz pass band), then averaged for 2 min synchronously with electrocardiogram's peaks taken from both hands. Noise remaining after the average is about 1.8 pTrms for the band-width of 0.16–100 Hz. The QRS complex and the T-wave are clearly detected.
    Print ISSN: 0021-8979
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  • 72
    Publication Date: 2015-04-25
    Description: A dc magnetoelectric sensor operating in ac voltage driving mode is developed based on a piezoelectric–magnetostrictive heterostructure having four thickness-polarized Pb(Zr, Ti)O 3 piezoelectric plates bonded symmetrically on a length-magnetized Tb 0.3 Dy 0.7 Fe 1.92 magnetostrictive plate to give an electrically parallel input and an electrically series output. The dc magnetic field sensing in the sensor is evaluated theoretically and experimentally and is found to originate from a unique ac voltage-driven, dc magnetic field-tuned resonance dc magnetoelectric effect in the heterostructure. An interestingly high, linear, and negative ac voltage-controlled dc magnetic field sensitivity of −1.3 mV/Oe/V is obtained in a broad range of dc magnetic field of 0–400 Oe by referencing an ac voltage of ≤5 V peak amplitude and 116 kHz frequency at the input of the heterostructure.
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  • 73
    Publication Date: 2015-04-25
    Description: We report on a micromagnetic study on the dynamics of current-driven helical domain wall (DW) in cylindrical NiFe nanowires. The helical DW is a three-dimensional transition region between magnetizations with clockwise and anticlockwise vortex orientations. A minimum current density is needed to overcome an intrinsic pinning to drive the helical DW, and the propagation along the nanowire is accompanied by a rotational motion. As the driving current strength is increased, the rotation ceases while the DW propagates at an increased velocity. However, a velocity barrier is experienced which results in the decrease of the DW mobility. Throughout its motion, the propagated helical DW maintains a stable profile without showing any sign of structural breakdown even at relatively high driving current.
    Print ISSN: 0021-8979
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  • 74
    Publication Date: 2015-04-25
    Description: Fe-6.5%Si alloy powders coated with manganese oxides using an innovative in situ process were investigated. The in-situ coating of the insulating oxides was realized with a KMnO 4 solution by a chemical process. The insulating manganese oxides with mixed valance state were verified by X-ray photoelectron spectroscopy analysis. The thickness of the insulating layer on alloy particles was determined to be in a range of 20–210 nm, depending upon the KMnO 4 concentration. The powder core loss and the change in permeability under a DC-bias field were measured at frequencies ranging from 50 to 100 kHz. The experiments indicated that the Fe-6.5%Si powder cores with a 210 nm-thick manganese oxide layer not only showed a low core loss of 459 mW/cm 3 at 100 kHz but also showed a small reduction in permeability (μ(H)/μ(0) = 85% for μ = 42) at a DC-bias field of 80 Oe. This work has defined a novel pathway to realizing low core loss and field-insensitive permeability for Fe-Si powder cores.
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  • 75
    Publication Date: 2015-04-25
    Description: Porous monodisperse spindle-like α-Fe 2 O 3 nanomaterials are first synthesized successfully by a hydrothermal method, and then the as-prepared nanoparticles are annealed at different temperatures under various atmospheres to achieve the spindle-like Fe 3 O 4 nanoparticles. The evolution of the features of nanoparticles, including the changes of the structures and microstructures as well as the magnetic properties, during the reduction process has been investigated by using the Raman spectrum and Mössbauer spectrum. Our research reveals that the α-Fe 2 O 3 nanoparticles annealed by covering of the C powder become a mixture of α-Fe 2 O 3 and Fe 3 O 4 in the range of annealing temperature from 300 °C to 800 °C. With reduced atmospheric H 2 , spindle-like α-Fe 2 O 3 nanoparticles are transferred to mixture of α-Fe 2 O 3 , Fe 3 O 4 and Fe as temperature increases. They are also converted from a typical rhombohedral structure to a cubic α-Fe phase at 500 °C. Finally, with the atmosphere of H 2 /Ar (5%/95%), a pure Fe 3 O 4 phase, and its excellent magnetic properties are achieved at 450 °C.
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  • 76
    Publication Date: 2015-04-25
    Description: Physical vapor deposition (PVD) has recently been investigated as a viable, alternative growth technique for two-dimensional materials with multiple benefits over other vapor deposition synthesis methods. The high kinetic energies and chemical reactivities of the condensing species formed from PVD processes can facilitate growth over large areas and at reduced substrate temperatures. In this study, chemistry, kinetic energies, time of flight data, and spatial distributions within a PVD plasma plume ablated from a boron nitride (BN) target by a KrF laser at different pressures of nitrogen gas were investigated. Time resolved spectroscopy and wavelength specific imaging were used to identify and track atomic neutral and ionized species including B + , B*, N + , N*, and molecular species including N 2 *, N 2 + , and BN. Formation and decay of these species formed both from ablation of the target and from interactions with the background gas were investigated and provided insights into fundamental growth mechanisms of continuous, amorphous boron nitride thin films. The correlation of the plasma diagnostic results with film chemical composition and thickness uniformity studies helped to identify that a predominant mechanism for BN film formation is condensation surface recombination of boron ions and neutral atomic nitrogen species. These species arrive nearly simultaneously to the substrate location, and BN formation occurs microseconds before arrival of majority of N + ions generated by plume collisions with background molecular nitrogen. The energetic nature and extended dwelling time of incident N + ions at the substrate location was found to negatively impact resulting BN film stoichiometry and thickness. Growth of stoichiometric films was optimized at enriched concentrations of ionized boron and neutral atomic nitrogen in plasma near the condensation surface, providing few nanometer thick films with 1:1 BN stoichiometry and good thicknesses uniformity over macroscopic areas.
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  • 77
    Publication Date: 2015-04-25
    Description: The promising thermoelectric material TiS 2 can be easily chemically doped and intercalated. We present here studies of single crystals that are intercalated with excess Ti or Co, or substituted with Ta. We demonstrate the intrinsic impact of these dopants on the thermal transport in the absence of grain boundary scattering. We show that Ta doping has the greatest impact on the thermal scattering rate per ion added, leading to a five-fold reduction in the lattice thermal conductivity as compared to stoichiometric single crystals.
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  • 78
    Publication Date: 2015-04-25
    Description: Molecular dynamics simulations were used to model the Eshelby dislocation inside Pd and Ir nanowires and to predict the powder diffraction pattern using the Debye scattering equation. We find that the ideal dislocation solution by Eshelby is in good agreement with the observed twist angle and deviatoric strain, even though it ignores both the splitting of the Eshelby dislocation into two partials and surface stress. Surface stress plays a significant role only for nanorods with small aspect ratio (∼1:1). We also find that Wilson's prediction on the diffraction peak broadening for the Eshelby dislocation is overestimated because it ignores the fact that the Eshelby twist relaxes the deviatoric strain. Moreover, the twist loosens the correlation along the nanorod, causing additional line profile broadening, which is read by diffraction as a decrease of coherent domain size when the total twist angle is bigger than 1.5°. Overall, our findings suggest a novel way to predict and analyze the dislocations as well as the resulting strain fields in the twisted nanocrystalline rods.
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  • 79
    Publication Date: 2015-04-25
    Description: Magnetic phase transition in the Fe 60 Al 40 transition metal aluminide from the ferromagnetic disordered A2-phase to the paramagnetic ordered B2-phase as a function of annealing up to 1000 °C has been investigated by means of magneto-optical and spectroscopy techniques, i.e., Kerr effect, positron annihilation, and Mössbauer spectroscopy. The positron annihilation spectroscopy has been performed in-situ sequentially after each annealing step at the Apparatus for In-situ Defect Analysis that is a unique tool combining positron annihilation spectroscopy with temperature treatment, material evaporation, ion irradiation, and sheet resistance measurement techniques. The overall goal was to investigate the importance of the open volume defects onto the magnetic phase transition. No evidence of variation in the vacancy concentration in matching the magnetic phase transition temperature range (400–600 °C) has been found, whereas higher temperatures showed an increase in the vacancy concentration.
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  • 80
    Publication Date: 2015-04-25
    Description: The fluid phase diagram of trimer particles composed of one central attractive bead and two repulsive beads was determined as a function of simple geometric parameters using flat-histogram Monte Carlo methods. A variety of self-assembled structures were obtained including spherical micelle-like clusters, elongated clusters, and densely packed cylinders, depending on both the state conditions and shape of the trimer. Advanced simulation techniques were employed to determine transitions between self-assembled structures and macroscopic phases using thermodynamic and structural definitions. Simple changes in particle geometry yield dramatic changes in phase behavior, ranging from macroscopic fluid phase separation to molecular-scale self-assembly. In special cases, both self-assembled, elongated clusters and bulk fluid phase separation occur simultaneously. Our work suggests that tuning particle shape and interactions can yield superstructures with controlled architecture.
    Print ISSN: 0021-9606
    Electronic ISSN: 1089-7690
    Topics: Chemistry and Pharmacology , Physics
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  • 81
    Publication Date: 2015-04-25
    Description: Cross-membrane electron transport between cofactors localized in proteins of mitochondrial respiration and bacterial photosynthesis is the source of all biological energy. The statistics and dynamics of nuclear fluctuations in these protein/membrane/water heterogeneous systems are critical for their energetic efficiency. The results of 13 μ s of atomistic molecular dynamics simulations of the membrane-bound bc 1 bacterial complex are analyzed here. The reaction is affected by a broad spectrum of nuclear modes, with the slowest dynamics in the range of time-scales ∼0.1-1.6 μ s contributing half of the reaction reorganization energy. Two reorganization energies are required to describe protein electron transfer due to dynamical arrest of protein conformations on the observation window. This mechanistic distinction allows significant lowering of activation barriers for reactions in proteins.
    Print ISSN: 0021-9606
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    Topics: Chemistry and Pharmacology , Physics
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