bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical investigation of flow-induced rotary oscillation of circular cylinder with rigid splitter plate
Authors: Lu Lin , Guo Xiao-ling , Tang Guo-qiang , Liu Ming-ming , Chen Chuan-qi , Xie Zhi-hua
Published: September 2016

Numerical results of fluid flow over a rotationally oscillating circular cylinder with splitter plate are presented here. Different from the previous examinations with freely rotatable assembly, the fluid and structure interactions are treated as a coupled dynamic system by fully considering the structural inertia, stiffness, and damping. The hydrodynamic characteristics are examined in terms of reduced velocity Ur at a relatively low Reynolds number Re = 100 for different plate lengths of L/D = 0.5, 1.0, and 1.5, where Ur = U/(Dfn), Re = UD/υ and fn = (κ/J)0.5/2π with U the free stream velocity, D the diameter of the circular cylinder, υ the fluid kinematic viscosity, fn the natural frequency, J the inertial moment, κ the torsional stiffness, and L the plate length. Contrast to the freely rotating cylinder/plate body, that is, in the limit of κ → 0 or Ur →∞, remarkable rotary oscillation is observed at relatively low reduced velocities. For the typical case with L/D = 1.0, the maximum amplitude may reach five times that at the highest reduced velocity of Ur = 15.0 considered in this work. At the critical reduced velocity Ur = 4.2, notable hydrodynamic jumps are identified for the rotation amplitude, response frequency, mean drag coefficient, lift amplitude, and vortex shedding frequency. Moreover, the phase angle between the fluid moment and rotary oscillation abruptly changes from 0 to π at Ur = 6.5. Due to the combined effect of fluid moment, rotation response, and phase difference, the natural frequency of the rotating body varies in flow, leading to a wide regime of lock-in/synchronization (Ur ≥4.2, for L/D = 1.0). The phenomenon of rotation bifurcation, i.e., the equilibrium position of the rotary oscillation deflects to a position which is not parallel to the free stream, is found to only occur at higher reduced velocities. The longer splitter plate has the lower critical reduced velocity. The occurrence of bifurcation is attributed to the anti-symmetry breaking of the wake flow evolution. The resultant asymmetric mean pressure distribution on the splitter plate gives rise to the net lift force and the deviated moment on the assembly, leading to the offset mean position of splitter plate. The global vortex shedding is identified to be the classic 2S mode for both cases with and without the bifurcation, although the second vortex formation and the shedding pattern in the near wake for the bifurcate case are different from the non-bifurcate case with lower reduced velocities.
High-power ultrafast Yb:fiber laser frequency combs using commercially available components and basic fiber tools
Authors: Li Xinlong , Reber Melanie A. R. , Corder Christopher , Chen Yuning , Zhao Peng , Allison Thomas K.
Published: September 2016

We present a detailed description of the design, construction, and performance of high-power ultrafast Yb:fiber laser frequency combs in operation in our laboratory. We discuss two such laser systems: an 87 MHz, 9 W, 85 fs laser operating at 1060 nm and an 87 MHz, 80 W, 155 fs laser operating at 1035 nm. Both are constructed using low-cost, commercially available components, and can be assembled using only basic tools for cleaving and splicing single-mode fibers. We describe practical methods for achieving and characterizing low-noise single-pulse operation and long-term stability from Yb:fiber oscillators based on nonlinear polarization evolution. Stabilization of the combs using a variety of transducers, including a new method for tuning the carrier-envelope offset frequency, is discussed. High average power is achieved through chirped-pulse amplification in simple fiber amplifiers based on double-clad photonic crystal fibers. We describe the use of these combs in several applications, including ultrasensitive femtosecond time-resolved spectroscopy and cavity-enhanced high-order harmonic generation.
Simulations of sawtoothing in a current carrying stellarator
Authors: Roberds N. A. , Guazzotto L. , Hanson J. D. , Herfindal J. L. , Howell E. C. , Maurer D. A. , Sovinec C. R.
Published: September 2016

Numerical MHD simulations are used to gain insight into how sawteeth are affected by three-dimensional shaping from the Compact Toroidal Hybrid (CTH) stellarator field. CTH is a small stellarator-tokamak hybrid and sawteeth are sometimes seen on soft x-ray signals when operating with tokamak like profiles. We use NIMROD to compute numerical solutions having repeated sawtooth relaxations for a sequence of configurations with increasing helical stellarator field strength. The experimentally observed trend of the sawtooth period decreasing as the helical field strength is increased is recovered in the simulations. Careful attention to numerical convergence was required to obtain the results, and these considerations may be relevant to simulations of other phenomena in devices with non-axisymmetric plasmas such as perturbed tokamaks, RFPs, and stellarators.
Using binary optical elements (BOEs) to generate rectangular spots for illumination in micro flow cytometer
Authors: Zhao Jingjing , You Zheng
Published: September 2016

This work introduces three rectangular quasi-flat-top spots, which are provided by binary optical elements (BOEs) and utilized for the illumination in a microflow cytometer. The three spots contain, respectively, one, two, and three rectangles (R1, R2, and R3). To test the performance of this mechanism, a microflow cytometer is established by integrating the BOEs and a three-dimensional hydrodynamic focusing chip. Through the experiments of detecting fluorescence microbeads, the three spots present good fluorescence coefficients of variation in comparison with those derived from commercial instruments. Benefiting from a high spatial resolution, when using R1 spot, the micro flow cytometer can perform a throughput as high as 20 000 events per second (eps). Illuminated by R2 or R3 spot, one bead emits fluorescence twice or thrice, thus the velocity can be measured in real time. Besides, the R3 spot provides a long-time exposure, which is conducive to improving fluorescence intensity and the measurement stability. In brief, using the spots shaped and homogenized by BOEs for illumination can increase the performance and the functionality of a micro flow cytometer.
Single-cell bacterium identification with a SOI optical microcavity
Authors: Tardif M. , Jager J.-B. , Marcoux P. R. , Uchiyamada K. , Picard E. , Hadji E. , Peyrade D.
Published: September 2016

Photonic crystals and microcavities act as on-chip nano-optical tweezers for identification and manipulation of biological objects. Until now, optical trapping of virus and bacteria has been achieved and their presence in the vicinity of the optical resonator is deduced by the shift in the resonant wavelength. Here, we show trapping and identification of bacteria through a properly tuned silicon on insulator microcavity. Through the spatial and temporal observations of bacteria–cavity interaction, the optical identification of three different kinds of bacteria is demonstrated.
Photoinduced intermolecular dynamics and subsequent fragmentation in VUV-ionized acetamide clusters
Authors: Tarkanovskaja Marta , Kooser Kuno , Levola Helena , Nõmmiste Ergo , Kukk Edwin
Published: September 2016

Photofragmentation of small gas-phase acetamide clusters (CH3CONH2)n (n ≤ 10) produced by a supersonic expansion source has been studied using time-of-flight ion mass spectroscopy combined with tunable vacuum-ultraviolet (VUV) synchrotron radiation. Fragmentation channels of acetamide clusters under VUV photoionization resulting in protonated and ammoniated clusters formation were identified with the discussion about the preceding intramolecular rearrangements. Acetamide-2,2,2-d3 clusters were also studied in an experiment with a gas discharge lamp as a VUV light source; comparison with the main experiment gave insights into the mechanism of formation of protonated acetamide clusters, indicating that proton transfer from amino group plays a dominant role in that process. Geometry of the acetamide dimer was discussed and the most stable arrangement was concluded to be achieved when subunits of the dimer are connected via two N—H⋯O —C hydrogen bonds. Also, the influence of the photon energy on the stability of the clusters and their fragmentation channels has been examined.
Characteristic study of head-on collision of dust-ion acoustic solitons of opposite polarity with kappa distributed electrons
Authors: Parveen Shahida , Mahmood Shahzad , Adnan Muhammad , Qamar Anisa
Published: September 2016

The head on collision between two dust ion acoustic (DIA) solitary waves, propagating in opposite directions, is studied in an unmagnetized plasma constituting adiabatic ions, static dust charged (positively/negatively) grains, and non-inertial kappa distributed electrons. In the linear limit, the dispersion relation of the dust ion acoustic (DIA) solitary wave is obtained using the Fourier analysis. For studying characteristic head-on collision of DIA solitons, the extended Poincaré-Lighthill-Kuo method is employed to obtain Korteweg–de Vries (KdV) equations with quadratic nonlinearities and investigated the phase shifts in their trajectories after the interaction. It is revealed that only compressive solitary waves can exist for the positive dust charged concentrations while for negative dust charge concentrations both the compressive and rarefactive solitons can propagate in such dusty plasma. It is found that for specific sets of plasma parameters, the coefficient of nonlinearity disappears in the KdV equation for the negative dust charged grains. Therefore, the modified Korteweg–de Vries (mKdV) equations with cubic nonlinearity coefficient, and their corresponding phase shift and trajectories, are also derived for negative dust charged grains plasma at critical composition. The effects of different plasma parameters such as superthermality, concentration of positively/negatively static dust charged grains, and ion to electron temperature ratio on the colliding soliton profiles and their corresponding phase shifts are parametrically examined.
Laser pulse compression and intensity enhancement in plasma
Authors: Gupta Pradeep Kumar , Sharma Swati , Gaur Nidhi , Singh Ram Kishor , Sharma R. P. , Uma R.
Published: September 2016

We present modeling of laser pulse compression and intensity enhancement during propagation in underdense plasma having relativistic intensity. Pulse duration shortens to less than 5 fs and 11 times intensity enhancement has been reported. Nonlinearity of plasma generates new frequency by self phase modulation which broadens the frequency spectrum of the pulse that in turn shortens the pulse duration. High intensity pulse pushes the velocity of electrons up to relativistic limit which in turn modifies the dielectric constant of plasma. Modification of the refractive index profile causes the self focusing of laser pulse. Pulse duration shortening and intensity enhancement happen in accordance with length of the plasma medium and density of the plasma.
Front surface field formation for majority carriers by functional p-NiO layer employed Si solar cell
Authors: Patel Dipal B. , Kim Hong-Sik , Patel Malkeshkumar , Chauhan Khushbu R. , Park Jeong Eun , Lim Donggun , Kim Joondong
Published: September 2016

An optically transparent and electrically conductive p-NiO layer was deposited on a conventional n-Si/p-Si solar cell, which improved the device performance. The transmittance and reflectance properties of the p-NiO layer were found to be much better than the SiNx layer in the visible light region. Impedance spectroscopic study under varying bias and illumination conditions was carried out to understand the underlying mechanisms governing the device performance. An AC signal analysis revealed that the p-NiO layer acted as a front surface field region for majority charge carriers. In addition, the p-NiO layer significantly improved Si solar cell performances due to the improved properties of parasitic resistances. The optically transparent NiO layered Si device (p-NiO/n-Si/p-Si) spontaneously enhanced the electrical properties, resulting in the substantially improved fill factor value of 74% from 34.3% of the bare n-Si/p-Si device. The existence of a front surface field increased the lifetime of carriers to 92 μs for the p-NiO/n-Si/p-Si solar cell compared to only 43 μs for an n-Si/p-Si cell. We may suggest a functional NiO layer to the efficient designs for Si solar cells.
Raman spectroscopy based measurements of carrier concentration in n-type GaN nanowires grown by plasma-assisted molecular beam epitaxy
Authors: Robins L. H. , Horneber E. , Sanford N. A. , Bertness K. A. , Brubaker M. D. , Schlager J. B.
Published: September 2016

The carrier concentration in as-grown ensembles of n-type GaN nanowires was determined by Raman spectroscopy of the coupled longitudinal phonon–plasmon (LPP+) mode and modeling of the carrier concentration dependence of the LPP+ frequency. The Raman measurements and analyses enabled estimation of the carrier concentration in single-nanowire devices fabricated from the as-grown ensembles. The nanowires were grown by plasma-assisted molecular beam epitaxy in either of the two growth systems. Twelve samples were examined, of which 11 samples were Si-doped and one was undoped. The Raman-measured carrier concentrations in the Si-doped samples ranged from (5.28 ± 1.19) × 1016 cm−3 to (6.16 ± 0.35) × 1017 cm−3. For a subset of samples grown with varying Si cell temperature, from 1125 °C to 1175 °C, the carrier concentration was found to be an Arrhenius function of Si cell temperature, with activation energy of 6.281±0.011 eV. Co-illumination by an above band gap UV laser (325 nm, excitation intensity = 0.7 W/cm2 or 4.5 W/cm2) induced small increases in carrier concentration, relative to illumination by the Raman excitation laser alone (633 nm, excitation intensity ≈100 kW/cm2). The lowest Si-doped sample showed the largest increase in carrier concentration, (6.3 ± 4.8) × 1015 cm−3 with UV excitation intensity of 0.7 W/cm2. These results imply that, even in the absence of UV illumination, surface depletion does not have a significant effect on the Raman carrier concentration measurements. Immersion in a high-dielectric-constant oil (ε = 2.24) caused downshifts of similar magnitude in the LPP+ frequencies of undoped and doped nanowires. This result implies that the LPP+ mode has bulk plasmon rather than surface plasmon character, because immersion in a high-dielectric-constant medium is predicted to cause a large decrease in the surface plasmon frequency, which would induce a larger LPP+ downshift in doped than undoped nanowires. A surface optical (SO) phonon peak was observed in each sample in air at ≈96.4% of the LPP+ frequency. The SO frequency decreased to ≈93.1% of the LPP+ frequency upon oil immersion, as predicted by a simple dielectric model.
Dynamics of multiphase turbulent plumes with hybrid buoyancy sources in stratified environments
Authors: Fabregat Tomàs Alexandre , Poje Andrew C. , Özgökmen Tamay M. , Dewar William K.
Published: September 2016

Deepwater oil blowouts typically generate multiphase hybrid plumes where the total inlet buoyancy flux is set by the combined presence of gas, oil, and heat. We numerically investigate the effects of combined sources of inlet buoyancy on turbulent plume dynamics by varying the inputs of a dispersed, slipping gas phase and a non-slipping buoyant liquid phase in thermally stratified environments. The ability of a single momentum equation, multiphase model to correctly reproduce characteristic plume heights is validated for both dispersed liquid phase and pure gas bubble plumes. A hybrid case, containing buoyancy contributions from both gas and liquid phases, is also investigated. As expected, on the plume centerline, the presence of a slipping gas phase increases both the vertical location of the neutrally buoyant equilibrium height and the maximum vertical extent of the liquid effluent relative to non-bubble plumes. While producing an overall increase in the plume height, the presence of a slipping gas phase also significantly enhances both the extent and magnitude of negatively buoyant downdrafts in the outer plume region. As a result, the intrusion or trapping height, the vertical distance where liquid phase plume effluent accumulates, is found to be significantly lower in both bubble and hybrid plumes. Below the intrusion level, the simulations are compared to an integral model formulation that explicitly accounts for the effects of the gas slip velocity in the evolution of the buoyancy flux. Discrepancies in the integral model and full solutions are largest in the source vicinity region where vertical turbulent volume fluxes, necessarily neglected in the integral formulation, are significant.
Control of mechanical response of freestanding PbZr0.52Ti0.48O3 films through texture
Authors: Das Debashish , Sanchez Luz , Martin Joel , Power Brian , Isaacson Steven , Polcawich Ronald G. , Chasiotis Ioannis
Published: September 2016

The texture of piezoelectric lead zirconate titanate (PZT) thin films plays a key role in their mechanical response and linearity in the stress vs. strain behavior. The open circuit mechanical properties of PZT films with controlled texture varying from 100% (001) to 100% (111) were quantified with the aid of direct strain measurements from freestanding thin film specimens. The texture was tuned using a highly {111}-textured Pt substrate and excess-Pb in the PbTiO3 seed layer. The mechanical and ferroelastic properties of 500 nm thick PZT (52/48) films were found to be strongly dependent on grain orientation: the lowest elastic modulus of 90 ± 2 GPa corresponded to pure (001) texture, and its value increased linearly with the percentage of (111) texture reaching 122 ± 3 GPa for pure (111) texture. These elastic modulus values were between those computed for transversely isotropic textured PZT films by using the soft and hard bulk PZT compliance coefficients. Pure (001) texture exhibited maximum non-linearity and ferroelastic domain switching, contrary to pure (111) texture that exhibited more linearity and the least amount of switching. A micromechanics model was employed to calculate the strain due to domain switching. The model fitted well the non-linearities in the experimental stress–strain curves of (001) and (111) textured PZT films, predicting 17% and 10% of switched 90° domains that initially were favorably aligned with the applied stress in (001) and (111) textured PZT films, respectively.
Measurement of contact angles in a simulated microgravity environment generated by a large gradient magnetic field
Authors: Liu Yong-Ming , Chen Rui-Qing , Wu Zi-Qing , Zhu Jing , Shi Jian-Yu , Lu Hui-Meng , Shang Peng , Yin Da-Chuan
Published: September 2016

The contact angle is an important parameter that is essential for studying interfacial phenomena. The contact angle can be measured using commercially available instruments. However, these well-developed instruments may not function or may be unsuitable for use in some special environments. A simulated microgravity generated by a large gradient magnetic field is such an environment in which the current measurement instruments cannot be installed. To measure the contact angle in this environment, new tools must be designed and manufactured to be compatible with the size and physical environment. In this study, we report the development and construction of a new setup that was specifically designed for use in a strong magnetic field to measure the contact angle between a levitated droplet and a solid surface. The application of the setup in a large gradient magnetic field was tested, and the contact angles were readily measured.
Ion temperature anisotropy due to perpendicular heating by Alfvén wave propagating along magnetic field lines
Authors: Choi C.-R. , Woo M.-H. , Dokgo K. , Min K.-W. , Lee D.-Y. , Yoon Peter H. , Hwang J. , Lee J.-J. , Park Y.-D.
Published: September 2016

The perpendicular heating and acceleration of ions by linearly polarized Alfvén wave, which is propagating along constant background magnetic field, is studied. The perpendicular diffusion coefficient of ions is calculated through the autocorrelation function based on linear perturbation theory, which unambiguously demonstrates that ion heating is attained by non-resonant wave-particle interaction. It is found that the perpendicular heating and acceleration of ions occur by the Alfvén wave during a relatively short time interval, i.e., approximately 20 ion gyro period (Ωi0t) even though the perturbation amplitude is quite low. Also, it is shown that the temperature anisotropy of ions A, where A=T⊥/T∥−1, increases with the increasing perturbation amplitude while the parallel ion heating does not occur. Test particle simulation is also carried out in order to investigate the non-resonant perpendicular heating process.
A many-body GW + BSE investigation of electronic and optical properties of C2N
Authors: Sun Jiuyu , Zhang Ruiqi , Li Xingxing , Yang Jinlong
Published: September 2016

A recently synthesized layered material C2N was investigated based on many-body perturbation theory using the GW plus Bethe-Salpeter equation approach. The electronic band gap was determined to be ranging from 3.75 to 1.89 eV from the monolayer to the bulk. Significant GW quasiparticle corrections, of more than 0.9 eV, to the Kohn-Sham band gaps from the local density approximation calculations are found. Strong excitonic effects play a crucial role in optical properties. We found large binding energies of greater than 0.6 eV for bound excitons in few-layer C2N, while it is only 0.04 eV in bulk C2N. All the structures exhibit strong and broad optical absorption in the visible light region, which makes C2N a promising candidate for solar energy conversion, such as photocatalytic water splitting.
Nonequilibrium interpretation of DC properties of NbN superconducting hot electron bolometers
Authors: Shcherbatenko M. , Tretyakov I. , Lobanov Yu. , Maslennikov S. N. , Kaurova N. , Finkel M. , Voronov B. , Goltsman G. , Klapwijk T. M.
Published: September 2016

We present a physically consistent interpretation of the dc electrical properties of niobiumnitride (NbN)-based superconducting hot-electron bolometer mixers, using concepts of nonequilibrium superconductivity. Through this, we clarify what physical information can be extracted from the resistive transition and the dc current-voltage characteristics, measured at suitably chosen temperatures, and relevant for device characterization and optimization. We point out that the intrinsic spatial variation of the electronic properties of disordered superconductors, such as NbN, leads to a variation from device to device.
Band gap narrowing in ferroelectric KNbO3-Bi(Yb,Me)O3 (Me=Fe or Mn) ceramics
Authors: Pascual-Gonzalez Cristina , Schileo Giorgio , Feteira Antonio
Published: September 2016

The direct optical bandgap in ferroelectric KNbO3-Bi(Yb,Me)O3 (Me = Fe or Mn) ceramics fabricated by the solid state reaction method varies from 3.2 eV for KNbO3 down to 2.2 eV for 0.95KNbO3-0.05BiYbO3, as revealed by optical spectroscopic ellipsometry. This narrowing of bandgap is accompanied by an apparent increase of the room-temperature relative permittivity from 320 for KNbO3 to 900 for 0.95KNbO3-0.05BiYbO3. All compositions studied exhibit dielectric anomalies associated with structural phase transitions, and their ferroelectric nature is corroborated by the presence of a sharp mixed mode (at ∼190 cm−1) and by a Fano-type resonant dip in their Raman spectra.
A new flexible titanium foil cell for hydrothermal experiments and fluid sampling
Authors: Wu Shi-Jun , Cai Min-Jian , Yang Can-Jun , Li Ke-Wei
Published: September 2016

This paper describes the design of a flexible titanium foil cell, as well as its applications in hydrothermal experiments and in non-contaminating storage of seafloor hydrothermal fluids. A flexible cell constructed totally from pure titanium (Grade 1) can be used in corrosive environment because of the excellent chemical stability and temperature tolerance of the material. Theoretical calculation and finite element analysis of the titanium foil cell have been conducted to identify its flexibility and deformation mode. Two applications, i.e., hydrothermal reaction and non-contaminating fluid sampling, were introduced subsequently. The flexible titanium foil cell was successfully tested at elevated temperature and pressure of up to 400 °C and 40 MPa, respectively, demonstrating that it could be widely used under supercritical water conditions.
Note: Electro-optic coefficients of Li-deficient MgO-doped LiNbO3 crystal
Authors: Du Wan-Ying , Zhang Zi-Bo , Ren Shuai , Wong Wing-Han , Yu Dao-Yin , Pun Edwin Yue-Bun , Zhang De-Long
Published: September 2016

A number of Li-deficient MgO-doped LiNbO3 (LN) crystals with different Li2O contents ranging from 43.4 mol. % to 44.5 mol. % were prepared by carrying out the Li-poor vapor transport equilibration treatment on 5 mol. % (in growth melt) MgO-doped LN crystals. Unclamped electro-optic (EO) coefficients γ13 and γ33 of these crystals were measured by Mach-Zehnder interferometry. The results show that γ13 (γ33) increases linearly by ∼14% (11%) as the Li2O content decreases from 44.5 mol. % of the as-grown state to 43.4 mol. % of the Li-deficient state. This feature is desired for the EO application of the Li-deficient MgO:LN crystal.
Basal-plane thermal conductivity of nanocrystalline and amorphized thin germanane
Authors: Coloyan Gabriella , Cultrara Nicholas D. , Katre Ankita , Carrete Jesús , Heine Matt , Ou Eric , Kim Jaehyun , Jiang Shishi , Lindsay Lucas , Mingo Natalio , Broido David , Heremans Joseph P. , Goldberger Joshua , Shi Li
Published: September 2016

Germanane (GeH), a hydrogen-terminated layered germanium structure, has recently been synthesized. Here, we employed a four-probe thermal transport measurement method to obtain the basal-plane thermal conductivity of thin exfoliated GeH flakes and correlated the measurement results with the crystal structure. The obtained thermal conductivity increases with increasing temperature, suggesting that extrinsic grain boundary and defect scattering dominate over intrinsic phonon-phonon scattering. Annealing a polycrystalline GeH sample at 195 °C caused it to become amorphous, reducing the room-temperature thermal conductivity from 0.53 ± 0.09 W m−1 K−1, which is close to the value calculated for 16 nm grain size, to 0.29 ± 0.05 W m−1 K−1, which approaches the calculated amorphous limit in the basal plane thermal conductivity.
The effect of seed electrons on the repeatability of atmospheric pressure plasma plume propagation: I. Experiment
Authors: Nie L. , Chang L. , Xian Y. , Lu X.
Published: September 2016

One of the significant differences between the traditional streamers and the plasma jets is the repeatability of their propagation. In this paper, the effect of the seed electron density on the repeatability of the plasma jets is investigated. The seed electron density plays an essential role in the propagation of plasma plume which is in either repeatable mode or random mode depending on the frequency of the applied voltage and the mixture percentage of the working gas. By measuring the propagation velocities and the ignition delay time, it is found that the propagation velocities of the plasma plume are independent of the seed electron density. However, the jitter of the ignition delay time strongly depends on the frequency of the applied voltage and the mixture percentage of the working gas. After detailed analyzing of the experiment results, it is concluded that the minimum seed electron density required for the plasma bullet to propagate in repeatable mode is on the order of 108 cm−3 for gas pressure of 2 × 104 Pa. The minimum required seed electron density for the gas pressure of 4 × 103 Pa is on the order of 107 cm−3. Further analysis shows that, at one atmospheric pressure, the required minimum seed electron density for repeatable mode is on the order of 109 cm−3.
Hysteresis loops revisited: An efficient method to analyze ferroic materials
Authors: Corbellini Luca , Plathier Julien , Lacroix Christian , Harnagea Catalin , Ménard David , Pignolet Alain
Published: September 2016

Hysteresis loops characterize a wide variety of behaviors in fields ranging from physics and chemistry to economics and sociology. In particular, they represent the main characteristic of ferroic materials such as ferromagnetic and ferroelectric, which, in recent years, have attracted much interest due to their multifunctional properties. Although measuring such loops may not be experimentally complicated, extracting the intrinsic values of the characteristic parameters of the loop may prove difficult due to the different contributions to the measured hysteresis. In this paper, a simple technique is proposed to analyze hysteresis loops and to extract solely the contribution of the ferromagnetic or ferroelectric material. Such method consists in differentiating the measured loop, deconvoluting the different contributions and selectively integrating only the signals belonging to the ferroic response. A discussion of the limitations of the method is presented. Different measured ferromagnetic and ferroelectric hysteresis loops were also used to validate the technique. Comparison between experimental and reconstructed data demonstrated the precision and reliability of the technique. Moreover, application of such method allowed us to highlight properties of a Bi2FeCrO6 room temperature multiferroic thin film that were not previously observed.
Control and prediction for blackouts caused by frequency collapse in smart grids
Authors: Wang Chengwei , Grebogi Celso , Baptista Murilo S.
Published: September 2016

The electric power system is one of the cornerstones of modern society. One of its most serious malfunctions is the blackout, a catastrophic event that may disrupt a substantial portion of the system, playing havoc to human life and causing great economic losses. Thus, understanding the mechanisms leading to blackouts and creating a reliable and resilient power grid has been a major issue, attracting the attention of scientists, engineers, and stakeholders. In this paper, we study the blackout problem in power grids by considering a practical phase-oscillator model. This model allows one to simultaneously consider different types of power sources (e.g., traditional AC power plants and renewable power sources connected by DC/AC inverters) and different types of loads (e.g., consumers connected to distribution networks and consumers directly connected to power plants). We propose two new control strategies based on our model, one for traditional power grids and another one for smart grids. The control strategies show the efficient function of the fast-response energy storage systems in preventing and predicting blackouts in smart grids. This work provides innovative ideas which help us to build up a robuster and more economic smart power system.
Non-contact magnetically coupled rectilinear-rotary oscillations to exploit low-frequency broadband energy harvesting with frequency up-conversion
Authors: Deng Wei , Wang Ya
Published: September 2016

Ambient vibrations have a rectilinear and broadband nature and are particularly rich in the low-frequency regions. This letter reports an electromagnetic energy harvester to transform low-frequency broadband rectilinear vibrations into electricity with frequency up-conversion. The harvester consists of a rectilinear oscillator and a rotary oscillator coupled through magnetic force induced by four arc permanent magnets centrosymmetrically distributed on each oscillator. The rotary oscillator also includes two repulsive magnets and six stationary coils with steel screws inside to obtain and maintain four equilibrium positions with shallowed potential wells. The magnetic interaction between the rectilinear oscillator and the rotary oscillator is formulated using a magnetic dipole model. The restoring torque induced by the steel screws on the rotor is experimentally measured. Magnetically coupled governing equations are derived and their numerical solutions are used to characterize the dynamic response of the harvester under chirp excitations. Experimental results demonstrate its excellent harvesting capability of scavenging low-frequency wideband vibrational energy under slow-frequency-drifted excitations, simple harmonic excitations, and mixed-frequency excitations. Under harmonic excitations, the rectilinear oscillator vibrates non-harmonically but approximately periodically, while the rotary counterpart oscillates in a more complex pattern varying with the excitation frequency, which leads to the frequency up-conversion (up to 10 times increase) and broadened bandwidth (25% increase from its resonant frequency). Experiments show an output voltage of 5 V (RMS)/40 V (Peak to Peak) and an output power of 55 mW (RMS)/950 mW (Peak) at an optimal load of 465 Ω under harmonic excitation of 4 Hz at 0.7 g.
Tailoring thermal conductivity of AlN films by periodically aligned surface nano-grooves
Authors: Zhang Xiaoliang , Gong Xiaojing , Zhou Yanguang , Hu Ming
Published: September 2016

Low thermal conductivity in condensed matter is critical to a diverse range of technologies, such as high efficient thermoelectrics and thermal insulation. It is thus important to fabricate, grow, or assemble structures that can reach a low limit. For III-nitride with high intrinsic thermal conductivity, how to utilize periodic nanostructures to manipulate phonons and achieve controllable low thermal conductivity is rarely studied. Recently, periodically self-organized arrays of nano-grooves on AlN (0001) surface have been observed experimentally. Inspired by this, we perform non-equilibrium molecular dynamics simulations to explore the thermal transport in such structures. The dependence of thermal conductivity on the periodic length of the nano-grooves and the angle of the side wall is systematically studied. Remarkably, results show that the thermal conductivity has a minimum value for a critical periodic length, which is one order of magnitude lower than the counterpart bulk value. The intrinsic high thermal conductivity of AlN can be robustly manipulated to the desired value by rationally designing the periodic nano-groove structure on the surface of the film. The detailed mechanism is provided by the frequency dependent heat current spectrum and phonon polarization analysis, along with the semi-empirical theoretical model. The understanding gained from this study offers an alternative route for tailoring the thermal conductivity of nanofilms by periodically patterned nano-grooves, which has large impact in relevant applications involving thermal transport.
Methodology to set up nozzle-to-substrate gap for high resolution electrohydrodynamic jet printing
Authors: Park Jaehong , Park Ji-Woon , Nasrabadi Ali Mohamadi , Hwang Jungho
Published: September 2016

Several efforts have been made for the prediction of jet diameter in electrohydrodynamic jet printing; however, not much attention has been paid to the jet length, which is the distance from the cone apex to the location where the jet is unstable and is broken into atomized droplets. In this study, we measured both the cone length and the jet length using a high-speed camera, and measured the line pattern width with an optical microscope to investigate the effects of cone length and jet length on the pattern quality. Measurements were carried out with variations in nozzle diameter, flow rate, and applied voltage. The pattern width was theoretically predicted for the case when the nozzle-to-substrate distance was more than the cone length, and smaller than the summation of the cone and jet lengths (which is the case when there is no jet breakup).
Experimental and first-principles study of the electronic transport properties of strained Bi2Te3 thin films on a flexible substrate
Authors: Inamoto Takuya , Takashiri Masayuki
Published: September 2016

On the basis of an experimental and first-principles study, strain effects on the thermoelectric properties of bismuth telluride (Bi2Te3) thin films were investigated. Bi2Te3 thin films were deposited on flexible polyimide substrates using a radio frequency magnetron sputtering method at a substrate temperature of 200 °C. Prior to deposition, various compressive and tensile bending strains were applied to the films by changing the bending radii of the flexible substrates. The structural and thermoelectric properties of the completed samples were analyzed. It was found that the lattice parameters of all samples exhibited smaller values compared to that of standard data for Bi2Te3 (JCPDS 15-0863) because the substrates might have shrunk during the film deposition, indicated by the fact that all the samples presented various compressive lattice strains. A theoretical analysis was performed using the first-principles study based on density functional theory. We calculated the electronic band structures for Bi2Te3 with the different lattice strains and predicted the thermoelectric properties based on the semi-classical Boltzmann transport equation in the rigid band approximation. The lowest conduction band edge in the Bi2Te3 band structure narrowed as the compressive lattice strain increased, indicating that the effective mass became smaller. Finally, the experimentally measured thermoelectric properties were compared with those obtained by the calculation. It was found that the calculated results were in good agreement with the experimental results.
Dramatically enhanced electrical breakdown strength in cellulose nanopaper
Authors: Huang Jianwen , Zhou Yuanxiang , Zhou Zhongliu , Liu Rui
Published: September 2016

Electrical breakdown behaviors of nanopaper prepared from nanofibrillated cellulose (NFC) were investigated. Compared to conventional insulating paper made from micro softwood fibers, nanopaper has a dramatically enhanced breakdown strength. Breakdown field of nanopaper is 67.7 kV/mm, whereas that of conventional paper is only 20 kV/mm. Air voids in the surface of conventional paper are observed by scanning electron microscope (SEM). Further analyses using mercury intrusion show that pore diameter of conventional paper is around 1.7 μm, while that of nanopaper is below 3 nm. Specific pore size of nanopaper is determined to be approximately 2.8 nm by the gas adsorption technique. In addition, theoretical breakdown strengths of nanopaper and conventional paper are also calculated to evaluate the effect of pore size. It turns out that theoretical values agree well with experimental data, indicating that the improved strength in nanopaper is mainly attributed to the decreased pore size. Due to its outstanding breakdown strength, this study indicates the suitability of nanopaper for electrical insulation in ultra-high voltage convert transformers and other electrical devices.
The Influence of Water Activity on the Growth of Rhizoctonia Solani
Authors: Dubé RL Dodman AJ , Flentje NT
Published: September 2016

The growth of R. solani on agar decreased from 7�5 to 0 mm/day with reduction in water activity from 0�995 to 0�960. Growth differed slightly when sucrose was used as a solute, as compared with a salt mixture, to produce a number of water activities. The effects of decreasing water activity were similar with a number of isolates of R. solani.
Symptoms of Scald Disease Induced by Toxic Metabolites of Rhynchosporium Secalis
Authors: Ayesu-Offei EN , Clare BG
Published: September 2016

Scald is a disease of barley and some grasses caused by the fungus Rhynchos-porium secalis (Oud.) Davis. Lesions on naturally or artificially infected leaves begin as grey, water-soaked areas 8-12 days after inoculation. Frequently, lesions at this stage become dry but retain a grey-green colour which persists even when the un-infected parts of a leaf have become senescent and straw-coloured. More usually the lesions become oval-shaped with dry, pale-brown or white centres surrounded by dark-brown margins. We have also observed signs of hypersensitive reactions in artificially and naturally infected barley leaves. The hypersensitive reactions result in the formation of small dark-brown patches on the leaves where infection has been unsuccessful.
Proliferation and apoptosis processes in the seasonal testicular development of the wild Daurian ground squirrel (Citellus dauricus Brandt, 1844)
Authors: Han Yingying , Zhan Jinqi , Xu Ying , Zhang Fengwei , Yuan Zhengrong , Weng Qiang
Published: September 2016

The aim of the present study was to elucidate the regulatory role of cell proliferation and apoptosis in testicular development of wild Daurian ground squirrels during the breeding season (April), the non-breeding season (June) and before hibernation (September). Gross mass and hormonal analysis showed that the testis : body mass ratio and plasma testosterone concentration fluctuated seasonally, with a peak in April and lowest values in June. Similarly, spermatogenesis was fully developed in April but suppressed in June and September. Testicular decellularisation and vacuolisation was seen during the transition from the breeding to the non-breeding season. Furthermore, testicular levels of proliferating cell nuclear antigen, cyclin D2 and caspase-3 protein were significantly increased in June and September. Intriguingly, positive terminal deoxyribonucleotidyl transferase-mediated dUTP–digoxigenin nick end-labelling staining and nuclear translocation of caspase-3 in testicular germ cells appeared only during the prehibernation period, whereas accumulation of cyclin D2 in spermatocyte nuclei occurred in September. These findings demonstrate, for the first time, that both cell proliferation and apoptosis are stimulated during the prehibernation period, indicating that a hormonal-regulated balance of testicular germ cell proliferation and apoptosis may play a pivotal role in preparing for testicular recrudescence of wild Daurian ground squirrels.
Sperm antioxidant defences decrease during epididymal transit from caput to cauda in parallel with increases in epididymal fluid in the goat (Capra hircus)
Authors: Rana Mashidur , Roy Sudhir C. , Divyashree Bannur C.
Published: September 2016

The status of antioxidant defences of both spermatozoa and their associated fluids during epididymal transit from the caput to cauda have not been studied so far in any species. Herein we report for the first time that sperm antioxidant defences, namely Cu,Zn-superoxide dismutase (Cu,Zn-SOD) and catalase activity, decrease significantly (P < 0.05) from the caput to cauda during epididymal transit in parallel with increases in Cu,Zn-SOD, total SOD and total glutathione peroxidase (GPx) activity in the luminal fluid of the respective segments. However, levels of GPX1 and GPX3 in epididymal fluid did not change significantly from the caput to cauda. Catalase was detected for the first time in goat spermatozoa. A significantly higher total antioxidant capacity of caudal fluid than of the caput suggests a requirement for a rich antioxidant environment for the storage of spermatozoa. The retention of cytoplasmic droplets in most of the caudal spermatozoa confirmed that these droplets do not contribute to the increased antioxidant defences of cauda epididymidal fluid. Thus, the antioxidant defences of the spermatozoa and their associated epididymal fluid are modulated from the caput to cauda in a region-specific manner. This may be one of the compensatory mechanisms of epididymal fluid to scavenge any excess reactive oxygen species produced in the microenvironment of spermatozoa.
Blue protein with red fluorescence
Authors: Ghosh Swagatha , Yu Chi-Li , Ferraro Daniel J. , Sudha Sai , Pal Samir Kumar , Schaefer Wayne F. , Gibson David T. , Ramaswamy S.
Published: September 2016

Significance

Recently it has been observed that the North American walleye is turning blue. The increased blue color is an adaptation to increased exposure to UV radiation. We identified that the blue pigment (Sandercyanin) is a complex of a protein and biliverdin—a breakdown product of heme. We report here that the blue pigment shows bright red fluorescence when excited with UV light. Elucidation of crystal structures and spectral properties of Sandercyanin lead us to hypothesize that the protection to damaging UV radiation happens by absorption of the UV light and its emission in the lower energy red wavelength. Interestingly, one can think of a number of applications where ligand-induced red fluorescent proteins can be useful.
Transparent antifouling material for improved operative field visibility in endoscopy
Authors: Sunny Steffi , Cheng George , Daniel Daniel , Lo Peter , Ochoa Sebastian , Howell Caitlin , Vogel Nicolas , Majid Adnan , Aizenberg Joanna
Published: September 2016

Significance

Inspection devices are frequently occluded by highly contaminating fluids that disrupt the visual field and their effective operation. These issues are particularly striking in endoscopes, where the diagnosis and treatment of diseases are compromised by the obscuring of the operative field by body fluids. Here we demonstrate that the application of a liquid-infused surface coating strongly repels sticky biological secretions and enables an uninterrupted field of view. Extensive bronchoscopy procedures performed in vivo on a porcine model shows significantly reduced fouling, resulting in either unnecessary or ∼10–15 times shorter and less intensive lens clearing procedures compared with an untreated endoscope.
Dissection of molecular assembly dynamics by tracking orientation and position of single molecules in live cells
Authors: Mehta Shalin B. , McQuilken Molly , La Riviere Patrick J. , Occhipinti Patricia , Verma Amitabh , Oldenbourg Rudolf , Gladfelter Amy S. , Tani Tomomi
Published: September 2016

Significance

In living cells, the 3D architecture of molecular assemblies, such as chromosomes, lipid bilayers, and the cytoskeleton, is regulated through the interaction among their component molecules. Monitoring the position and orientation of constituent molecules is important for understanding the mechanisms that govern the structure and function of these assemblies. We have developed an instantaneous fluorescence polarization microscope to track the position and orientation of fluorescently labeled particles, including single molecules, which form micrometer-scale macromolecular assemblies in living cells. Our imaging approach is broadly applicable to the study of dynamic molecular interactions that underpin the function of micrometer-scale assemblies in living cells.
Miro phosphorylation sites regulate Parkin recruitment and mitochondrial motility
Authors: Shlevkov Evgeny , Kramer Tal , Schapansky Jason , LaVoie Matthew J. , Schwarz Thomas L.
Published: September 2016

Significance

In mitophagy, damaged mitochondria stabilize PTEN-induced putative kinase 1 (PINK1) and recruit Parkin, an E3-ligase that ubiquitinates proteins on the outer membrane and targets mitochondria for degradation. The crucial roles of PINK1 phosphorylation of Parkin and ubiquitin in mitophagy are well-established. Other substrates of PINK1, however, have also been reported but the significance of those phosphorylations is less clear. We now show that Miro phosphorylations can regulate Parkin recruitment to Miro and trigger Miro degradation. The consequence of this branch of the PINK1/Parkin pathway is the disruption of mitochondrial motility, an event that may spatially restrict the deleterious effects of mitochondrial damage prior to the mitophagic removal of the organelle.