bluuebunny/crossref_metadata_2025 huggingface dataset:
Design and implementation of a high‐performance technique for tracking PV peak power
Authors: Belkaid Abdelhakim , Gaubert Jean‐Paul , Gherbi Ahmed
Published: July 2016

Most maximum power point tracking (MPPT) techniques based on sliding‐mode control (SMC) use another method such as perturb and observe or incremental conductance (IncCond) to provide current or voltage reference which makes the system more complex. To reduce the complexity and to increase the photovoltaic (PV) array efficiency, a direct control high‐performance MPPT based on improved SMC has been investigated in this study. Using two different step sizes can follow the PV peak power at different operating conditions with rapid convergence and greater accuracy. The new SMC‐based MPPT designed for boost‐type DC/DC converters is compared with a conventional and modified IncCond method, and to a classical SMC method which is very similar to that applied by Chu et al. The proposed PV‐MPPT system is tested during a stringent profile of sunshine variation as recommended by the European Norm 50530, by simulation within MATLAB/SimulinkTM tools and verified by implementation using a test bench based on DS1104 R&D controller board. The obtained results are satisfactory and demonstrate that the new SMC can track the MPP quickly within 0.003 s and with good accuracy close to 99%.
Analysis of the hot-cavity mode composition of an X-band overmoded relativistic backward wave oscillators
Authors: Yuan Yuzhang , Zhang Jun , Zhong Huihuang , Zhang Dian
Published: July 2016

Overmoded RBWO (Relativistic Backward Wave Oscillators) is utilized more and more often for its high power capacity. However, both sides of SWS (Slow Wave Structure) of overmoded RBWO consist multi TM0n modes; in order to achieve the design of reflector, it is essential to make clear of the mode composition of TM0n. NUDT (National University of Defence Technology) had done research of the output mode composition in overmoded O-type Cerenkov HPM (High Power Microwave) Oscillators in detail, but in the area where the electron beam exists, the influence of electron beam must be taken into account. Hot-cavity dispersion equation is figured out in this article first, and then analyzes the hot-cavity mode composition of an X-band overmoded RBWO tentatively. The results show that in collimating hole, the hot-cavity mode analysis is more accurate.
High resolution spectroscopy of jet cooled phenyl radical: The ν1 and ν2 a1 symmetry C–H stretching modes
Authors: Chang Chih-Hsuan , Nesbitt David J.
Published: July 2016

A series of CH stretch modes in phenyl radical (C6H5) has been investigated via high resolution infrared spectroscopy at sub-Doppler resolution (∼60 MHz) in a supersonic discharge slit jet expansion. Two fundamental vibrations of a1 symmetry, ν1 and ν2, are observed and rotationally analyzed for the first time, corresponding to in-phase and out-of-phase symmetric CH stretch excitation at the ortho/meta/para and ortho/para C atoms with respect to the radical center. The ν1 and ν2 band origins are determined to be 3073.968 50(8) cm−1 and 3062.264 80(7) cm−1, respectively, which both agree within 5 cm−1 with theoretical anharmonic scaling predictions based on density functional B3LYP/6-311g++(3df,3dp) calculations. Integrated band strengths for each of the CH stretch bands are analyzed, with the relative intensities agreeing remarkably well with theoretical predictions. Frequency comparison with previous low resolution Ar-matrix spectroscopy [A. V. Friderichsen et al., J. Am. Chem. Soc. 123, 1977 (2001)] reveals a nearly uniform Δν ≈ + 10-12 cm−1 blue shift between gas phase and Ar matrix values for ν1 and ν2. This differs substantially from the much smaller red shift (Δν ≈ − 1 cm−1) reported for the ν19 mode, and suggests a simple physical model in terms of vibrational mode symmetry and crowding due to the matrix environment. Finally, the infrared phenyl spectra are well described by a simple asymmetric rigid rotor Hamiltonian and show no evidence for spectral congestion due to intramolecular vibrational coupling, which bodes well for high resolution studies of other ring radicals and polycyclic aromatic hydrocarbons. In summary, the combination of slit jet discharge methods with high resolution infrared lasers enables spectroscopic investigation of even highly reactive combustion and interstellar radical intermediates under gas phase, jet-cooled (Trot ≈ 11 K) conditions.
Ultrafast photodynamics of pyrazine in the vacuum ultraviolet region studied by time-resolved photoelectron imaging using 7.8-eV pulses
Authors: Horio Takuya , Suzuki Yoshi-ichi , Suzuki Toshinori
Published: July 2016

The ultrafast electronic dynamics of pyrazine (C4N2H4) were studied by time-resolved photoelectron imaging (TRPEI) using the third (3ω, 4.7 eV) and fifth harmonics (5ω, 7.8 eV) of a femtosecond Ti:sapphire laser (ω). Although the photoionization signals due to the 5ω − 3ω and 3ω − 5ω pulse sequences overlapped near the time origin, we have successfully extracted their individual TRPEI signals using least squares fitting of the observed electron kinetic energy distributions. When the 5ω pulses preceded the 3ω pulses, the 5ω pulses predominantly excited the S4 (ππ*, 1B1u+1B2u) state. The photoionization signal from the S4 state generated by the time-delayed 3ω pulses was dominated by the D3(2B2g)←S4 photoionization process and exhibited a broad electron kinetic energy distribution, which rapidly downshifted in energy within 100 fs. Also observed were the photoionization signals for the 3s, 3pz, and 3py members of the Rydberg series converging to D0(2Ag). The Rydberg signals appeared immediately within our instrumental time resolution of 27 fs, indicating that these states are directly photoexcited from the ground state or populated from S4 within 27 fs. The 3s, 3pz, and 3py states exhibited single exponential decay with lifetimes of 94 ± 2, 89 ± 2, and 58 ± 1 fs, respectively. With the reverse pulse sequence of 3ω − 5ω, the ultrafast internal conversion (IC) from S2(ππ*) to S1(nπ*) was observed. The decay associated spectrum of S2 exhibited multiple bands ascribed to D0, D1, and D3, in agreement with the 3ω-pump and 6ω-probe experiment described in our preceding paper [T. Horio et al., J. Chem. Phys. 145, 044306 (2016)]. The electron kinetic energy and angular distributions from S1 populated by IC from S2 are also discussed.
Studies of spuriously shifting resonances in time-dependent density functional theory
Authors: Luo Kai , Fuks Johanna I. , Maitra Neepa T.
Published: July 2016

Adiabatic approximations in time-dependent density functional theory (TDDFT) will in general yield unphysical time-dependent shifts in the resonance positions of a system driven far from its ground-state. This spurious time-dependence is explained in Fuks et al. [Phys. Rev. Lett. 114, 183002 (2015)] in terms of the violation of an exact condition by the non-equilibrium exchange-correlation kernel of TDDFT. Here we give details on the derivation and discuss reformulations of the exact condition that apply in special cases. In its most general form, the condition states that when a system is left in an arbitrary state, the TDDFT resonance position for a given transition in the absence of time-dependent external fields and ionic motion is independent of the state. Special cases include the invariance of TDDFT resonances computed with respect to any reference interacting stationary state of a fixed potential, and with respect to any choice of appropriate stationary Kohn-Sham reference state. We then present several case studies, including one that utilizes the adiabatically exact approximation, that illustrate the conditions and the impact of their violation on the accuracy of the ensuing dynamics. In particular, charge-transfer across a long-range molecule is hampered, and we show how adjusting the frequency of a driving field to match the time-dependent shift in the charge-transfer resonance frequency results in a larger charge transfer over time.
Nonlocal Newtonian cosmology
Authors: Chicone C. , Mashhoon B.
Published: July 2016

We explore some of the cosmological implications of the recent classical nonlocal generalization of Einstein’s theory of gravitation in which nonlocality is due to the gravitational memory of past events. In the Newtonian regime of this theory, the nonlocal character of gravity simulates dark matter in spiral galaxies and clusters of galaxies. However, dark matter is considered indispensable as well for structure formation in standard models of cosmology. Can nonlocal gravity solve the problem of structure formation without recourse to dark matter? Here we make a beginning in this direction by extending nonlocal gravity in the Newtonian regime to the cosmological domain. The nonlocal analog of the Zel’dovich solution is formulated and the consequences of the resulting nonlocal Zel’dovich model are investigated in detail.
Polycapillary lenses for soft x-ray transmission in ITER: Model, comparison with experiments, and potential application
Authors: Mazon D. , Liegeard C. , Jardin A. , Barnsley R. , Walsh M. , O’Mullane M. , Sirinelli A. , Dorchies F.
Published: July 2016

Measuring Soft X-Ray (SXR) radiation [0.1 keV; 15 keV] in tokamaks is a standard way of extracting valuable information on the particle transport and magnetohydrodynamic activity. Generally, the analysis is performed with detectors positioned close to the plasma for a direct line of sight. A burning plasma, like the ITER deuterium-tritium phase, is too harsh an environment to permit the use of such detectors in close vicinity of the machine. We have thus investigated in this article the possibility of using polycapillary lenses in ITER to transport the SXR information several meters away from the plasma in the complex port-plug geometry.
Multicomponent density functional theory embedding formulation
Authors: Culpitt Tanner , Brorsen Kurt R. , Pak Michael V. , Hammes-Schiffer Sharon
Published: July 2016

Multicomponent density functional theory (DFT) methods have been developed to treat two types of particles, such as electrons and nuclei, quantum mechanically at the same level. In the nuclear-electronic orbital (NEO) approach, all electrons and select nuclei, typically key protons, are treated quantum mechanically. For multicomponent DFT methods developed within the NEO framework, electron-proton correlation functionals based on explicitly correlated wavefunctions have been designed and used in conjunction with well-established electronic exchange-correlation functionals. Herein a general theory for multicomponent embedded DFT is developed to enable the accurate treatment of larger systems. In the general theory, the total electronic density is separated into two subsystem densities, denoted as regular and special, and different electron-proton correlation functionals are used for these two electronic densities. In the specific implementation, the special electron density is defined in terms of spatially localized Kohn-Sham electronic orbitals, and electron-proton correlation is included only for the special electron density. The electron-proton correlation functional depends on only the special electron density and the proton density, whereas the electronic exchange-correlation functional depends on the total electronic density. This scheme includes the essential electron-proton correlation, which is a relatively local effect, as well as the electronic exchange-correlation for the entire system. This multicomponent DFT-in-DFT embedding theory is applied to the HCN and FHF− molecules in conjunction with two different electron-proton correlation functionals and three different electronic exchange-correlation functionals. The results illustrate that this approach provides qualitatively accurate nuclear densities in a computationally tractable manner. The general theory is also easily extended to other types of partitioning schemes for multicomponent systems.
A comparative study of coarse-graining methods for polymeric fluids: Mori-Zwanzig vs. iterative Boltzmann inversion vs. stochastic parametric optimization
Authors: Li Zhen , Bian Xin , Yang Xiu , Karniadakis George Em
Published: July 2016

We construct effective coarse-grained (CG) models for polymeric fluids by employing two coarse-graining strategies. The first one is a forward-coarse-graining procedure by the Mori-Zwanzig (MZ) projection while the other one applies a reverse-coarse-graining procedure, such as the iterative Boltzmann inversion (IBI) and the stochastic parametric optimization (SPO). More specifically, we perform molecular dynamics (MD) simulations of star polymer melts to provide the atomistic fields to be coarse-grained. Each molecule of a star polymer with internal degrees of freedom is coarsened into a single CG particle and the effective interactions between CG particles can be either evaluated directly from microscopic dynamics based on the MZ formalism, or obtained by the reverse methods, i.e., IBI and SPO. The forward procedure has no free parameters to tune and recovers the MD system faithfully. For the reverse procedure, we find that the parameters in CG models cannot be selected arbitrarily. If the free parameters are properly defined, the reverse CG procedure also yields an accurate effective potential. Moreover, we explain how an aggressive coarse-graining procedure introduces the many-body effect, which makes the pairwise potential invalid for the same system at densities away from the training point. From this work, general guidelines for coarse-graining of polymeric fluids can be drawn.
The relative entropy is fundamental to adaptive resolution simulations
Authors: Kreis Karsten , Potestio Raffaello
Published: July 2016

Adaptive resolution techniques are powerful methods for the efficient simulation of soft matter systems in which they simultaneously employ atomistic and coarse-grained (CG) force fields. In such simulations, two regions with different resolutions are coupled with each other via a hybrid transition region, and particles change their description on the fly when crossing this boundary. Here we show that the relative entropy, which provides a fundamental basis for many approaches in systematic coarse-graining, is also an effective instrument for the understanding of adaptive resolution simulation methodologies. We demonstrate that the use of coarse-grained potentials which minimize the relative entropy with respect to the atomistic system can help achieve a smoother transition between the different regions within the adaptive setup. Furthermore, we derive a quantitative relation between the width of the hybrid region and the seamlessness of the coupling. Our results do not only shed light on the what and how of adaptive resolution techniques but will also help setting up such simulations in an optimal manner.
A high-stability non-contact dilatometer for low-amplitude temperature-modulated measurements
Authors: Luckabauer Martin , Sprengel Wolfgang , Würschum Roland
Published: July 2016

Temperature modulated thermophysical measurements can deliver valuable insights into the phase transformation behavior of many different materials. While especially for non-metallic systems at low temperatures numerous powerful methods exist, no high-temperature device suitable for modulated measurements of bulk metallic alloy samples is available for routine use. In this work a dilatometer for temperature modulated isothermal and non-isothermal measurements in the temperature range from room temperature to 1300 K is presented. The length measuring system is based on a two-beam Michelson laser interferometer with an incremental resolution of 20 pm. The non-contact measurement principle allows for resolving sinusoidal length change signals with amplitudes in the sub-500 nm range and physically decouples the length measuring system from the temperature modulation and heating control. To demonstrate the low-amplitude capabilities, results for the thermal expansion of nickel for two different modulation frequencies are presented. These results prove that the novel method can be used to routinely resolve length-change signals of metallic samples with temperature amplitudes well below 1 K. This high resolution in combination with the non-contact measurement principle significantly extends the application range of modulated dilatometry towards high-stability phase transformation measurements on complex alloys.
Insulation-resistance degradation kinetics of bulk BaTi1−ξAξO3−Δ and defect-chemical origin of acceptor-type(A) and doping-level(ξ) effect
Authors: Kwon Hyung-Soon , Yoon Seok-Hyun , Yoo Han-Ill
Published: July 2016

Dearth of the reproducible, consistent observations on insulation-resistance (IR) degradation kinetics of bulk dielectric BaTiO3 may be attributed to their conventional measurement method, two-probe potentiostatic, which would be by no means free from the electrode effect for a finite- dimension specimen in particular. We hereby measured the IR-degradation kinetics galvanostatically by using a series of inner probes on bulk BaTi1−ξAξO3−Δ (A = Al, Mn; ξ = 0.001, 0.003, 0.010) with their high-temperature (1000 °C) equilibrium ionic-defect-structure in air being frozen-in at 250 °C and compared with the kinetics as calculated on the basis of the electromigration of frozen-in oxygen vacancies (cVo) in association with the A-ionization or hole-trapping equilibria. It has turned out that the calculated depict sufficiently precisely all the as-observed kinetics as well as the effects of acceptor type(A) and doping level(ξ), thus, quantitatively establishing the correlation between the frozen-in ionic-defect-structure and IR-degradation kinetics with new insights into the degradation inner-workings: IR-degradation is triggered as soon as the oxygen vacancy concentration at the cathode reaches that corresponding to the insulator-to-semiconductor transition (cVS/I) and proceeds with the front of just-turned, n-type semiconducting region (cV=cVS/I) moving towards the anode at a fixed velocity. The healthy lifetime of the dielectric is, thus, essentially the time duration for the cathode to achieve cVS/I from cVo, and the final stage of degradation is approximated to be the length fraction χs of the semiconductor such that χs = cVo/cVS/I. A new suggestion is finally made to further suppress the IR degradation kinetics of the bulk dielectric BaTiO3.
A multi-scale study of the adsorption of lanthanum on the (110) surface of tungsten
Authors: Samin Adib J. , Zhang Jinsuo
Published: July 2016

In this study, we utilize a multi-scale approach to studying lanthanum adsorption on the (110) plane of tungsten. The energy of the system is described from density functional theory calculations within the framework of the cluster expansion method. It is found that including two-body figures up to the sixth nearest neighbor yielded a reasonable agreement with density functional theory calculations as evidenced by the reported cross validation score. The results indicate that the interaction between the adsorbate atoms in the adlayer is important and cannot be ignored. The parameterized cluster expansion expression is used in a lattice gas Monte Carlo simulation in the grand canonical ensemble at 773 K and the adsorption isotherm is recorded. Implications of the obtained results for the pyroprocessing application are discussed.
Effect of low temperature anneals and nonthermal treatments on the properties of gap fill oxides used in SiGe and III-V devices
Authors: Ryan E. Todd , Morin Pierre , Madan Anita , Mehta Sanjay
Published: July 2016

Silicon dioxide is used to electrically isolate CMOS devices such as fin field effect transistors by filling gaps between the devices (also known as shallow trench isolation). The gap fill oxide typically requires a high temperature anneal in excess of 1000 °C to achieve adequate electrical properties and oxide densification to make the oxide compatible with subsequent fabrication steps such as fin reveal etch. However, the transition from Si-based devices to high mobility channel materials such as SiGe and III-V semiconductors imposes more severe thermal limitations on the processes used for device fabrication, including gap fill oxide annealing. This study provides a framework to quantify and model the effect of anneal temperature and time on the densification of a flowable silicon dioxide as measured by wet etch rate. The experimental wet etch rates allowed the determination of the activation energy and anneal time dependence for oxide densification. Dopant and self-diffusion can degrade the channel material above a critical temperature. We present a model of self-diffusion of Ge and Si in SiGe materials. Together these data allowed us to map the thermal process space for acceptable oxide wet etch rate and self-diffusion. The methodology is also applicable to III-V devices, which require even lower thermal budget. The results highlight the need for nonthermal oxide densification methods such as ultraviolet (UV) and plasma treatments. We demonstrate that several plasma treatments, in place of high temperature annealing, improved the properties of flowable oxide. In addition, UV curing prior to thermal annealing enables acceptable densification with dramatically reduced anneal temperature.
A multiscale asymptotic analysis of time evolution equations on the complex plane
Authors: Braga Gastão A. , Conti William R. P.
Published: July 2016

Using an appropriate norm on the space of entire functions, we extend to the complex plane the renormalization group method as developed by Bricmont et al. The method is based upon a multiscale approach that allows for a detailed description of the long time asymptotics of solutions to initial value problems. The time evolution equation considered here arises in the study of iterations of the block spin renormalization group transformation for the hierarchical N-vector model. We show that, for initial conditions belonging to a certain Fréchet space of entire functions of exponential type, the asymptotics is universal in the sense that it is dictated by the fixed point of a certain operator acting on the space of initial conditions.
An architecture for integrating planar and 3D cQED devices
Authors: Axline C. , Reagor M. , Heeres R. , Reinhold P. , Wang C. , Shain K. , Pfaff W. , Chu Y. , Frunzio L. , Schoelkopf R. J.
Published: July 2016

Numerous loss mechanisms can limit coherence and scalability of planar and 3D-based circuit quantum electrodynamics (cQED) devices, particularly due to their packaging. The low loss and natural isolation of 3D enclosures make them good candidates for coherent scaling. We introduce a coaxial transmission line device architecture with coherence similar to traditional 3D cQED systems. Measurements demonstrate well-controlled external and on-chip couplings, a spectrum absent of cross-talk or spurious modes, and excellent resonator and qubit lifetimes. We integrate a resonator-qubit system in this architecture with a seamless 3D cavity, and separately pattern a qubit, readout resonator, Purcell filter, and high-Q stripline resonator on a single chip. Device coherence and its ease of integration make this a promising tool for complex experiments.
Transient enhancement of magnetization damping in CoFeB film via pulsed laser excitation
Authors: Liu Bo , Ruan Xuezhong , Wu Zhenyao , Tu Hongqing , Du Jun , Wu Jing , Lu Xianyang , He Liang , Zhang Rong , Xu Yongbing
Published: July 2016

Laser-induced spin dynamics of in-plane magnetized CoFeB films has been studied by using time-resolved magneto-optical Kerr effect measurements. While the effective demagnetization field shows little dependence on the pump laser fluence, the intrinsic damping constant has been found to be increased from 0.008 to 0.076 with the increase in the pump fluence from 2 mJ/cm2 to 20 mJ/cm2. This sharp enhancement has been shown to be transient and ascribed to the heating effect induced by the pump laser excitation, as the damping constant is almost unchanged when the pump-probe measurements are performed at a fixed pump fluence of 5 mJ/cm2 after irradiation by high power pump pulses.
A simple multipurpose double-beam optical image analyzer
Authors: Popowicz A. , Blachowicz T.
Published: July 2016

In the paper we present a low cost optical device which splits the light in the focal plane into two separate optical paths and collimates it back into a single image plane, and where a selective information processing can be carried out. The optical system is straightforward and easily implementable as it consists of only three lenses and two mirrors. The system is dedicated for imaging in low-light-level conditions in which widely used optical devices, based on beam splitters or dichroic mirrors, suffer from light loss. We expose examples of applications of our device, using a prototype model. The proposed optical system may be employed for: monitoring the objects located at different distances from observer (1), creating regions of different magnification within a single image plane (2), high dynamic range photometry (3), or imaging in two wavelength bands simultaneously (4).
On spinors transformations
Authors: Budinich Marco
Published: July 2016

We begin showing that for even dimensional vector spaces V all automorphisms of their Clifford algebras are inner. So all orthogonal transformations of V are restrictions to V of inner automorphisms of the algebra. Thus under orthogonal transformations P and T—space and time reversal—all algebra elements, including vectors v and spinors φ, transform as v → xvx−1 and φ → xφx−1 for some algebra element x. We show that while under combined PT spinor φ → xφx−1 remains in its spinor space, under P or T separately φ goes to a different spinor space and may have opposite chirality. We conclude with a preliminary characterization of inner automorphisms with respect to their property to change, or not, spinor spaces.
A simple laser locking system based on a field-programmable gate array
Authors: Jørgensen N. B. , Birkmose D. , Trelborg K. , Wacker L. , Winter N. , Hilliard A. J. , Bason M. G. , Arlt J. J.
Published: July 2016

Frequency stabilization of laser light is crucial in both scientific and industrial applications. Technological developments now allow analog laser stabilization systems to be replaced with digital electronics such as field-programmable gate arrays, which have recently been utilized to develop such locking systems. We have developed a frequency stabilization system based on a field-programmable gate array, with emphasis on hardware simplicity, which offers a user-friendly alternative to commercial and previous home-built solutions. Frequency modulation, lock-in detection, and a proportional-integral-derivative controller are programmed on the field-programmable gate array and only minimal additional components are required to frequency stabilize a laser. The locking system is administered from a host-computer which provides comprehensive, long-distance control through a versatile interface. Various measurements were performed to characterize the system. The linewidth of the locked laser was measured to be 0.7 ± 0.1 MHz with a settling time of 10 ms. The system can thus fully match laser systems currently in use for atom trapping and cooling applications.
High-throughput exploration of thermoelectric and mechanical properties of amorphous NbO2 with transition metal additions
Authors: Music Denis , Geyer Richard W. , Hans Marcus
Published: July 2016

To increase the thermoelectric efficiency and reduce the thermal fatigue upon cyclic heat loading, alloying of amorphous NbO2 with all 3d and 5d transition metals has systematically been investigated using density functional theory. It was found that Ta fulfills the key design criteria, namely, enhancement of the Seebeck coefficient and positive Cauchy pressure (ductility gauge). These quantum mechanical predictions were validated by assessing the thermoelectric and elastic properties on combinatorial thin films, which is a high-throughput approach. The maximum power factor is 2813 μW m−1 K−2 for the Ta/Nb ratio of 0.25, which is a hundredfold increment compared to pure NbO2 and exceeds many oxide thermoelectrics. Based on the elasticity measurements, the consistency between theory and experiment for the Cauchy pressure was attained within 2%. On the basis of the electronic structure analysis, these configurations can be perceived as metallic, which is consistent with low electrical resistivity and ductile behavior. Furthermore, a pronounced quantum confinement effect occurs, which is identified as the physical origin for the Seebeck coefficient enhancement.
Electrical four-point probing of spherical metallic thin films coated onto micron sized polymer particles
Authors: Pettersen Sigurd R. , Stokkeland August Emil , Kristiansen Helge , Njagi John , Redford Keith , Goia Dan V. , Zhang Zhiliang , He Jianying
Published: July 2016

Micron-sized metal-coated polymer spheres are frequently used as filler particles in conductive composites for electronic interconnects. However, the intrinsic electrical resistivity of the spherical thin films has not been attainable due to deficiency in methods that eliminate the effect of contact resistance. In this work, a four-point probing method using vacuum compatible piezo-actuated micro robots was developed to directly investigate the electric properties of individual silver-coated spheres under real-time observation in a scanning electron microscope. Poly(methyl methacrylate) spheres with a diameter of 30 μm and four different film thicknesses (270 nm, 150 nm, 100 nm, and 60 nm) were investigated. By multiplying the experimental results with geometrical correction factors obtained using finite element models, the resistivities of the thin films were estimated for the four thicknesses. These were higher than the resistivity of bulk silver.
Insight into magnetic, ferroelectric and elastic properties of strained BiFeO3 thin films through Mössbauer spectroscopy
Authors: Agbelele A. , Sando D. , Infante I. C. , Carrétéro C. , Jouen S. , Le Breton J.-M. , Barthélémy A. , Dkhil B. , Bibes M. , Juraszek J.
Published: July 2016

We have studied the magnetic order of highly strained (001)-oriented BiFeO3 (BFO) thin films using 57Fe Conversion Electron Mössbauer Spectrometry. From 90 K to 620 K the films exhibit a collinear antiferromagnetic structure, in contrast with the cycloidal structure observed in bulk BFO. Moreover, we find that both the planar magnetic anisotropy for compressive strain and out-of-plane anisotropy for tensile strain persist from 90 K up to the Néel temperature (TN), which itself shows only a weak strain dependence. An analysis of the line asymmetry of the paramagnetic doublet for temperatures above TN is used to reveal the strain-dependent rotation of the polarization direction, consistent with previous observations. Our results show that the lattice dynamics in BFO films are strongly strain-dependent, offering avenues toward acoustic phonon devices. Finally, we use the versatility of Mössbauer spectroscopy technique to reveal various multi-property features including magnetic states, polarization direction and elastic strain.
Laser-initiated explosive electron emission from flat germanium crystals
Authors: Porshyn V. , Mingels S. , Lützenkirchen-Hecht D. , Müller G.
Published: July 2016

Flat Sb-doped germanium (100) crystals were investigated in the triode configuration under pulsed tunable laser illumination (pulse duration tlaser = 3.5 ns and photon energy hν = 0.54–5.90 eV) and under DC voltages <104 V. Large bunch charges up to ∼1 μC were extracted from the cathodes for laser pulses >1 MW/cm2 corresponding to a high quantum efficiency up to 3.3% and cathode currents up to 417 A. This laser-induced explosive electron emission (EEE) from Ge was characterized by its voltage-, laser power- and hν-sensitivity. The analysis of the macroscopic surface damage caused by the EEE is included as well. Moreover, we have carried out first direct measurements of electron energy distributions produced during the EEE from the Ge samples. The measured electron spectra hint for electron excitations to the vacuum level of the bulk and emission from the plasma plume with an average kinetic energy of ∼0.8 eV.
Nano-eutectic structure formation and soft magnetic properties of bulk ternary Fe-B-M (M = Si, Cu) alloys
Authors: Huang Huili , Yang Changlin , Song Qijiao , Ye Ke , Liu Feng
Published: July 2016

The bulk Fe-B-M (M = Si, Cu) ternary eutectic alloys with nano-lamellar structure and excellent soft magnetic properties were successfully prepared by undercooling combined with Cu-mold casting. Different effects of Si and Cu elements on the structural refinement and soft magnetic properties were studied. The results show that the lamellar spacing can be decreased to less than 50 nm with addition of Si or Cu of 1 at. % into the Fe-B eutectic alloy. Based on the classical random anisotropy model, a quantitative correlation between the intrinsic coercivity (HC) and the lamellar spacing (λ) was also obtained.
Thermoacoustic and thermoreflectance imaging of biased integrated circuits: Voltage and temperature maps
Authors: Hernández-Rosales E. , Cedeño E. , Hernandez-Wong J. , Rojas-Trigos J. B. , Marin E. , Gandra F. C. G. , Mansanares A. M.
Published: July 2016

In this work a combined thermoacoustic and thermoreflectance set-up was designed for imaging biased microelectronic circuits. In particular, it was used with polycrystalline silicon resistive tracks grown on a monocrystalline Si substrate mounted on a test chip. Thermoreflectance images, obtained by scanning a probe laser beam on the sample surface, clearly show the regions periodically heated by Joule effect, which are associated to the electric current distribution in the circuit. The thermoacoustic signal, detected by a pyroelectric/piezoelectric sensor beneath the chip, also discloses the Joule contribution of the whole sample. However, additional information emerges when a non-modulated laser beam is focused on the sample surface in a raster scan mode allowing imaging of the sample. The distribution of this supplementary signal is related to the voltage distribution along the circuit.
Impact of recess etching and surface treatments on ohmic contacts regrown by molecular-beam epitaxy for AlGaN/GaN high electron mobility transistors
Authors: Joglekar S. , Azize M. , Beeler M. , Monroy E. , Palacios T.
Published: July 2016

Ohmic contacts fabricated by regrowth of n+ GaN are favorable alternatives to metal-stack-based alloyed contacts in GaN-based high electron mobility transistors. In this paper, the influence of reactive ion dry etching prior to regrowth on the contact resistance in AlGaN/GaN devices is discussed. We demonstrate that the dry etch conditions modify the surface band bending, dangling bond density, and the sidewall depletion width, which influences the contact resistance of regrown contacts. The impact of chemical surface treatments performed prior to regrowth is also investigated. The sensitivity of the contact resistance to the surface treatments is found to depend upon the dangling bond density of the sidewall facets exposed after dry etching. A theoretical model has been developed in order to explain the observed trends.
Conclusive evidence of abrupt coagulation inside the void during cyclic nanoparticle formation in reactive plasma
Authors: van de Wetering F. M. J. H. , Nijdam S. , Beckers J.
Published: July 2016

In this letter, we present scanning electron microscopy (SEM) results that confirm in a direct way our earlier explanation of an abrupt coagulation event as the cause for the void hiccup. In a recent paper, we reported on the fast and interrupted expansion of voids in a reactive dusty argon–acetylene plasma. The voids appeared one after the other, each showing a peculiar, though reproducible, behavior of successive periods of fast expansion, abrupt contraction, and continued expansion. The abrupt contraction was termed “hiccup” and was related to collective coagulation of a new generation of nanoparticles growing in the void using relatively indirect methods: electron density measurements and optical emission spectroscopy. In this letter, we present conclusive evidence using SEM of particles collected at different moments in time spanning several growth cycles, which enables us to follow the nanoparticle formation process in great detail.
Non-Maxwellian to Maxwellian transitions of atmospheric microplasmas at microwave frequencies
Authors: Lee M. U. , Jeong S. Y. , Won I. H. , Sung S. K. , Yun G. S. , Lee J. K.
Published: July 2016

Particle-in-cell/Monte Carlo simulations and numerical analysis of a single particle motion are performed for atmospheric He microplasmas at microwave frequencies to determine the characteristics of non-Maxwellian to Maxwellian transition. The left and the right regimes of Paschen curve, divided by this transition, reveal that the transition frequencies depend on the gap of electrodes and the neutral gas pressure to follow scaling laws for a new extended Paschen law. The fluid models are reasonable at the right-side regime of Paschen breakdown areas, but not on the left side, which is highly kinetic for electrons. The plasmas driven by weaker electric fields of high enough frequencies at the right-side Paschen regime breed more energetic electrons.
Acoustic levitation of a large solid sphere
Authors: Andrade Marco A. B. , Bernassau Anne L. , Adamowski Julio C.
Published: July 2016

We demonstrate that acoustic levitation can levitate spherical objects much larger than the acoustic wavelength in air. The acoustic levitation of an expanded polystyrene sphere of 50 mm in diameter, corresponding to 3.6 times the wavelength, is achieved by using three 25 kHz ultrasonic transducers arranged in a tripod fashion. In this configuration, a standing wave is created between the transducers and the sphere. The axial acoustic radiation force generated by each transducer on the sphere was modeled numerically as a function of the distance between the sphere and the transducer. The theoretical acoustic radiation force was verified experimentally in a setup consisting of an electronic scale and an ultrasonic transducer mounted on a motorized linear stage. The comparison between the numerical and experimental acoustic radiation forces presents a good agreement.
Random numbers from vacuum fluctuations
Authors: Shi Yicheng , Chng Brenda , Kurtsiefer Christian
Published: July 2016

We implement a quantum random number generator based on a balanced homodyne measurement of vacuum fluctuations of the electromagnetic field. The digitized signal is directly processed with a fast randomness extraction scheme based on a linear feedback shift register. The random bit stream is continuously read in a computer at a rate of about 480 Mbit/s and passes an extended test suite for random numbers.
Large spin-orbit torques in Pt/Co-Ni/W heterostructures
Authors: Yu Jiawei , Qiu Xuepeng , Legrand William , Yang Hyunsoo
Published: July 2016

The spin orbit torques (SOTs) in perpendicularly magnetized Co-Ni multilayers sandwiched between two heavy metals (HM) have been studied. By exploring various HM materials, we show an efficient enhancement or cancellation of the total SOT, depending on the combination of the two HM materials. The maximum SOT effective field is obtained in Pt/Co-Ni/W heterostructures. We also model our double HM system and show that the effective spin Hall angle has a peak value at certain HM thicknesses. Measuring the SOT in Pt/Co-Ni/W for various W thicknesses confirms an effective spin Hall angle up to 0.45 in our double HM system.
Preparation of ZnO/ZnSe heterostructure parallel arrays for photodetector application
Authors: Xiao Chuanhai , Wang Yuda , Yang Tianye , Luo Yang , Zhang Mingzhe
Published: July 2016

ZnO/ZnSe heterostructure parallel arrays on glass substrate were prepared through ultrathin layers electrodeposition method combining with annealing treatment. There are two essential factors for the formation of such kind of parallel arrays: the periodical change of charges and ions concentration, and the mutual equilibrium of electric repulsion at the growth front. The research for photoresponse characteristics of the heterostructure arrays demonstrates a UV/visible broad spectral response.
Nano-light-emitting-diodes based on InGaN mesoscopic structures for energy saving optoelectronics
Authors: Mikulics M. , Winden A. , Marso M. , Moonshiram A. , Lüth H. , Grützmacher D. , Hardtdegen H.
Published: July 2016

Vertically integrated III-nitride based nano-LEDs (light emitting diodes) were designed and fabricated for operation in the telecommunication wavelength range in the (p-GaN/InGaN/n-GaN/sapphire) material system. The band edge luminescence energy of the nano-LEDs could be engineered by tuning the composition and size of the InGaN mesoscopic structures. Narrow band edge photoluminescence and electroluminescence were observed. Our mesoscopic InGaN structures (depending on diameter) feature a very low power consumption in the range between 2 nW and 30 nW. The suitability of the technological process for the long-term operation of LEDs is demonstrated by reliability measurements. The optical and electrical characterization presented show strong potential for future low energy consumption optoelectronics.
Early-life disease exposure and associations with adult survival, cause of death, and reproductive success in preindustrial humans
Authors: Hayward Adam D. , Rigby Francesca L. , Lummaa Virpi
Published: July 2016

Significance

Why has human life expectancy increased since 1850? A leading hypothesis proposes that limited exposure to childhood infections has reduced lifelong inflammation and enhanced survival, but tests of this hypothesis typically use all-cause mortality rates to estimate disease exposure. Meanwhile, links between early-life disease and reproduction have been neglected. We used data from preindustrial Finnish populations to show that early-life disease exposure was not associated with all-cause mortality, mortality from cardiovascular disease, stroke, and cancer, or reproductive success. Our study therefore does not support the prevailing contention that reduced exposure to early-life infections has increased life expectancy in modern populations.
Earth’s oxygen cycle and the evolution of animal life
Authors: Reinhard Christopher T. , Planavsky Noah J. , Olson Stephanie L. , Lyons Timothy W. , Erwin Douglas H.
Published: July 2016

Significance

Earth is currently the only planet known to harbor complex life. Understanding whether terrestrial biotic complexity is a unique phenomenon or can be expected to be widespread in the universe depends on a mechanistic understanding of the factors that led to the emergence of complex life on Earth. Here, we use geochemical constraints and quantitative models to suggest that marine environments may have been unfavorable for the emergence and large-scale proliferation of motile multicellular life for most of Earth’s history. Further, we argue that a holistic evaluation of environmental variability, organismal life history, and spatial ecological dynamics is essential for a full accounting of the factors that have allowed for the emergence of biological complexity on Earth.
Flight paths of seabirds soaring over the ocean surface enable measurement of fine-scale wind speed and direction
Authors: Yonehara Yoshinari , Goto Yusuke , Yoda Ken , Watanuki Yutaka , Young Lindsay C. , Weimerskirch Henri , Bost Charles-André , Sato Katsufumi
Published: July 2016

Significance

Monitoring ocean surface winds is essential for understanding ocean and atmosphere interactions and weather forecasts. However, wind measured by satellite scatterometers and buoys are spatially and temporally coarse, particularly in coastal areas. We deployed small global positioning system units on soaring seabirds to record their tracks. Seabirds were accelerated by tail winds or slowed down by head winds during flight, so their flight speed changed in relation to wind speed and direction. Taking advantage of these changes in flight speed, we reliably estimated wind speed and direction experienced by the seabirds. The wind observed by soaring seabird’s tracks complemented the conventional observation gaps in terms of both time and space, suggesting the possibility of using soaring seabirds as a living anemometer.
The neural chaperone proSAAS blocks α-synuclein fibrillation and neurotoxicity
Authors: Jarvela Timothy S. , Lam Hoa A. , Helwig Michael , Lorenzen Nikolai , Otzen Daniel E. , McLean Pamela J. , Maidment Nigel T. , Lindberg Iris
Published: July 2016

Significance

Aberrant protein homeostasis (proteostasis) is increasingly recognized as a major causal factor in the development of protein aggregates, including aggregation of α-synuclein in Parkinson’s disease. Cellular proteins known as chaperones control proteostatic processes and are strongly associated with many different neurodegenerative diseases. We show here that an abundant brain- and endocrine-specific secretory chaperone known as proSAAS (named after four residues in the amino terminal region) exhibits potent antiaggregant effects on α-synuclein aggregation, and we identify a region of the protein that is necessary for this antiaggregant effect. We further show that proSAAS expression is able to stop α-synuclein from killing dopaminergic cells in a nigral cell model of Parkinson’s disease. This work demonstrates an important role for the proSAAS protein in blocking aggregation in neurodegeneration.
Stress and corticosteroids regulate rat hippocampal mitochondrial DNA gene expression via the glucocorticoid receptor
Authors: Hunter Richard G. , Seligsohn Ma’ayan , Rubin Todd G. , Griffiths Brian B. , Ozdemir Yildirim , Pfaff Donald W. , Datson Nicole A. , McEwen Bruce S.
Published: July 2016

Significance

Successful response to stress requires that an organism rapidly direct its energy toward an appropriate survival response. The brain is central to successful survival decisions, and therefore its ability to allocate energetic resources precisely in response to stress is paramount. Glucocorticoid stress hormones have long been known to assist in the liberation of energy during stress via their ability to regulate the activity of the nuclear genome. The cellular powerhouse, the mitochondria, also contains a genome; herein we show that glucocorticoids, acting through their receptors, regulate the expression of mitochondrial genes in the brain. These findings demonstrate a direct molecular linkage between stress and mitochondrial function.
Highly sensitive detection of influenza virus by boron-doped diamond electrode terminated with sialic acid-mimic peptide
Authors: Matsubara Teruhiko , Ujie Michiko , Yamamoto Takashi , Akahori Miku , Einaga Yasuaki , Sato Toshinori
Published: July 2016

Significance

A large number of people suffer from influenza every year. Early detection is critical for preventing severe influenza in high-risk groups. There is usually not enough time to produce vaccines against pandemic viruses before they spread to other countries. Anti-influenza therapy using neuraminidase inhibitors is effective within 30 h of the onset of symptoms. Here we show that several dozen plaque-forming units of influenza virus (IFV) are detectable by a boron-doped diamond electrode terminated with a sialic acid-mimic peptide with the ability to capture IFV. The electrode was sufficiently sensitive to detect IFV in specimens obtained in the early phase of infection. The device developed in the present work has potential applications in the highly sensitive detection of IFV to fight against influenza.
Complete in vitro generation of fertile oocytes from mouse primordial germ cells
Authors: Morohaku Kanako , Tanimoto Ren , Sasaki Keisuke , Kawahara-Miki Ryouka , Kono Tomohiro , Hayashi Katsuhiko , Hirao Yuji , Obata Yayoi
Published: July 2016

Significance

Throughout the life of female mammals, only a small number of viable oocytes are produced. The mechanisms underlying the creation and selection of competent oocytes remain unclear. Here, we propose a novel approach for elucidating these unsolved questions, involving the use of an in vitro system established in the present study, which can fully reproduce mammalian oogenesis from mouse fetal primordial germ cells. Reconstitution of the entire oogenesis process has not been previously accomplished. Our system will assist in understanding the mechanisms of oogenesis and also create a new gamete resource in mammals.