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We introduce and study the spatial replicator equation with higher order interactions and both infinite (spatially homogeneous) populations and finite (spatially inhomogeneous) populations. We show that in the special case of three strategies (rock–paper–scissors) higher order interaction terms allow travelling waves to emerge in non-declining finite populations. We show that these travelling waves arise from diffusion stabilisation of an unstable interior equilibrium point that is present in the aspatial dynamics. Based on these observations and prior results, we offer two conjectures whose proofs would fully generalise our results to all odd cyclic games, both with and without higher order interactions, assuming a spatial replicator dynamic. Intriguingly, these generalisations for N ⩾ 5 strategies seem to require declining populations, as we show in our discussion. [ABSTRACT FROM AUTHOR]

Stealthy coronal mass ejections (CMEs), lacking low coronal signatures, may result in significant geomagnetic storms. However, the mechanism of stealthy CMEs is still highly debated. In this work, we investigate whether there are differences between stealthy and standard CMEs in terms of their dynamic behaviors. Seven stealthy and eight standard CMEs with low speeds are selected. We calculate two-dimensional speed distributions of CMEs based on the cross-correlation method, rather than the unidimensional speed, and further obtain more accurate distributions and evolution of CME mechanical energies. Then we derive the CME driving powers and correlate them with CME parameters (total mass, average speed, and acceleration) for standard and stealthy CMEs. Besides, we study the forces that drive CMEs, namely, the Lorentz force, gravitational force, and drag force due to the ambient solar wind near the Sun. The results reveal that both standard and stealthy CMEs are propelled by the combined action of those forces in the inner corona. The drag force and gravitational force are comparable with the Lorentz force. However, the impact of the drag and Lorentz forces on the global evolution of stealthy CMEs is significantly weaker than that on standard CMEs. [ABSTRACT FROM AUTHOR]

The self-assembled growth of InAs/GaAs quantum dots by molecular beam epitaxy is conducted by optimizing several growth parameters, using a one-step interruption method after island formation. The dependence of photoluminescence on areal quantum-dot density is systematically investigated as a function of InAs deposition, growth temperature and arsenic pressure. The results of this investigation along with time-resolved photoluminescence measurements show that the combination of a growth temperature of 490 °C, with a deposition rate of 0.02 ML/s, under an arsenic pressure of 1 × 10−6 Torr (1 Torr = 1.33322 × 102 Pa), provides the best compromise between high density and the photoluminescence of quantum dot structure, with a radiative lifetime of 780 ps. The applicability of this 5-layer quantum dot structure to high-repetition-rate pulsed lasers is demonstrated with the fabrication and characterization of a monolithic InAs/GaAs quantum-dot passively mode-locked laser operating at nearly 1300 nm. Picosecond pulse generation is achieved from a two-section laser, with a ∼ 19.7-GHz repetition rate. [ABSTRACT FROM AUTHOR]

Compression of unmagnetized Nd2Fe14B permanent magnets is executed by using shock waves with different pressures in a one-stage light gas gun system. The microstructure, crystal structure, and magnetic properties of the magnets are examined with scanning electronic microscopy, x-ray diffraction, hysteresis loop instruments, and a vibrating sample magnetometer, respectively. The NdFeB magnets display a demagnetization phenomenon after shock wave compression. The coercivity dropped from about 21.4 kOe to 3.2 kOe. The critical pressure of irreversible demagnetization of NdFeB magnets should be less than 4.92 GPa. The coercivity of the NdFeB magnets compressed by shock waves could be recovered after annealing at 900°C and 520°C for 2 h, sequentially. The chaotic orientation of Nd2Fe14B grains in the compressed magnets is the source of demagnetization. [ABSTRACT FROM AUTHOR]

We investigate the transmission and backscattering of solitary waves in granular crystals to assess their initial strains under various levels of compression. We assemble a one-dimensional granular chain that includes a pair of heavy impurities to scatter incident solitary waves. Using a scanning laser Doppler vibrometer and an instrumented sensor particle, we experimentally show that the speed of solitary waves backscattered in the region of impurities is highly sensitive to the applied strains. Based on this pulse-echo mechanism of solitary waves, we briefly demonstrate the feasibility of localized strain sensing via multiple scatterers distributed in a granular chain. We find that numerical results obtained from a discrete element model are in excellent agreement with experimental results. This study forms a foundation for constructing a solitary wave-based sensor system to measure distributed strains in ordered granular systems. [ABSTRACT FROM AUTHOR]

The operational parameters including the polarization controlling and the pump power in a nonlinear polarization rotation-based passively mode-locked fiber laser are studied in this paper. The carrier rate equations of the activated erbium-doped fiber are first employed together with the nonlinear Shröodinger equations to reveal the relation between the operational parameters and the output state of the passively mode-locked fiber laser. The numerical and experimental results demonstrate that the output state of the mode-locked laser varies with the polarization controlling and the pump power. The periodicity of the polarization controlling is observed. With given pump power, there exists a set of polarization controlling under which the ultra-short pulse can be generated. With given polarization controlling, the mode-locked state can be maintained generally except for some particular values of pump power. Three shapes of the output optical spectra from the fiber cavity can be identified when the pump power changes. The results in this paper provide a comprehensive insight into the operation of the nonlinear polarization rotation-based passively mode-locked fiber laser. [ABSTRACT FROM AUTHOR]

The above-threshold ionization of argon in an intense 70-fs, 400-nm linearly polarized laser pulse has been investigated by the velocity map imaging techniques, combined with an attosecond-resolution quantum wave packet dynamics method. There is a quantitative agreement in all dominant features between the experiment and the theory. Moreover, a peak-splitting phenomenon in the first energy peak has been observed at high pulse intensity. Further, through the theoretical analysis, an ac Stark splitting with evident resonant and nonresonant ionization pathways has been found to be the physical reason for the experimental observations. [ABSTRACT FROM AUTHOR]

In the recent work of Kiss et al. [Phys. Rev. Lett. 107 (2011) 100501], the evolvement of two-qubit quantum states in a measurement-based purification process is studied. As they pointed out, the purification results manifest sensitivity to the applied initial states. The convergence regions to different stable circles are depicted on a complex plane. Because of the result patterns' likeness to typical fractals, we make further study on the interesting patterns' connection to fractals. Finally, through a numerical method we conclude that the boundaries of different islands of the patterns are fractals, which possess a non-integral fractal dimension. Also, we show that the fractal dimension would vary with the change of the portion of the noise added to the initial states. [ABSTRACT FROM AUTHOR]

In this paper, we theoretically investigate the effect of noise on the photoionization, the generation of the high-order harmonic and the attosecond pulse irradiated from a model He+ ion. It shows that by properly adding noise fields, such as Gaussian white noise, random light or colored noise, both the ionization probabilities (IPs) and the harmonic yields can be enhanced by several orders of magnitude. Further, by tuning the noise intensity, a stochastic resonance-like curve is observed, showing the existence of an optimal noise in the ionization enhancement process. Finally, by superposing a properly selected harmonic, an intense attosecond pulse with a duration of 67 as is directly generated. [ABSTRACT FROM AUTHOR]

In order to investigate the carrier redistribution mechanisms in InAs/GaAs self-assembled quantum dots, the photoluminescent energy peak shift is studied with increasing excitation power. Unusually for samples of relatively low density, it is shown that the energy peak position could recover slowly after a fast redshift, associated with the increasing excitation power. A theoretical model is presented, which involves the Auger effect assisting carrier recapture as important mechanisms during the relaxation process. [ABSTRACT FROM AUTHOR]

Theoretical studies on mode propagation and second harmonic generation in periodically poled MgO-doped LiNbO3 on an insulator (PPLNOI) rib waveguide are presented. With a special design, the waveguide can simultaneously support the single-mode propagation of both a pump wave (1550 nm) and a second harmonic wave (775 nm). As a result of the strong confinement and intensive nonlinear effect in the PPLNOI rib waveguide, the calculated results indicate that a second-harmonic generation conversion efficiency of 400%W-1·cm-1 can be achieved at a wavelength of 1550 nm, almost 2.6 times higher than the widely applied reverse proton-exchanged waveguide (150%W-1·cm-2). [ABSTRACT FROM AUTHOR]

Idea spreading is an important process in science and society. In this work, we study this spreading process in a population consisting of two groups based on a recent model proposed by Bornholdt et al. We consider two types of division in the population: regular and random division. We find some interesting phenomena, for example, the exchange of dominant ideas between the two groups in the cases of regular and the random division, and the appearance of a novel stage in which a few ideas interact strongly to seek a balance. [ABSTRACT FROM AUTHOR]

We report a systematic optical spectroscopy study of low density InAs quantum clusters (QCs) grown by molecular beam epitaxy. The photoluminescence (PL) spectra show emission features of a wetting layer (WL) which contains hybridized quantum well states. The low-energy tail of the QCs' PL profile is actually an ensemble of some sharp lines, originating from the emission of different exciton states (e.g. X, X*, XX*) in a single quasi-three-dimensional (Q3D) cluster as detailed in the micro-PL spectra. The temperature dependence of PL spectra indicates photocarrier distribution and transport in the QC-WL system. Furthermore, this small InAs Q3D cluster is integrated with a distributed Bragg reflector structure, and using optical excitation creates a single photon source with the second-order correlation function of g(2)(0) = 0:31 at 16 K. [ABSTRACT FROM AUTHOR]

Hierarchical structural symmetry of periodic islands embedded in the chaotic region of modified optical injection semiconductor lasers (MOISLs) is expounded upon in phase diagrams. The onset of the bifurcation cascade shows remarkable accumulation horizons. Each cascade follows a specific period-adding route. Self-similarities and infinite spiral nestings shrinking beyond a certain point of the periodic hub are revealed to affirm the existence of self-organized distribution of periodicity and chaos in phase diagrams. [ABSTRACT FROM AUTHOR]

In this paper, we investigate perfect quantum teleportation and dense coding by using an 2N-qubit W state channel. In the quantum teleportation scheme, an unknown N-qubit entangled state can be perfectly teleported. One ebit of entanglement and two bits of classical communication are consumed in the teleportation process, just like when using the Bell state channel. While N + 1 bits of classical information can be transmitted by only sending N particles in the dense coding protocol. [ABSTRACT FROM AUTHOR]

This paper reports that Cr2O3 hollow nanospheres (HNs) were synthesized via a hydrothermal approach and characterized by scanning electron microscopy, x-ray powder diffraction, transmission electron microscopy (TEM), selective area electron diffraction and high resolution TEM, respectively. In addition, the room-temperature (RT) gas sensing properties of Cr2O3 HNs and conventional powders (CPs) were investigated by means of the surface photovoltage technique. The experimental data demonstrate that the RT gas sensor of the as-fabricated HNs reaches below 5 ppm whereas that of the CPs is about 40 ppm, which results from there being much more adsorbed and desorbed oxygen in HNs than in CPs at RT. The as-prepared Cr2O3 HNs could have potential applications as RT nanosensors. [ABSTRACT FROM AUTHOR]

This paper develops a new phase-field model for equiaxed dendrite growth of multiple grains in multicomponent alloys based on the Ginzberg-Landau theory and phase-field model of a single grain. Taking Al-Cu and Al-Cu-Mg alloys for example, it couples the concentration field and simulates the dendrite growth process of multiple grains during isothermal solidification. The result of the simulation shows dendrite competitive growth of multiple grains, and is reapplied to the process of dendrite growth in practical solidification. [ABSTRACT FROM AUTHOR]

Pb1.17Te thermoelectric polycrystalline materials were fabricated by mechanical alloying (MA) and spark plasma sintering (SPS). The property measurement and microstructural characterization showed that the present material has special features different from traditional Pb1+xTe ingots with secondary Pb phase. An attractive enhancement of the thermoelectric figure of merit ZT = 0.64 was obtained at 450 K, with a low thermal conductivity of 1.11 W m[?]1 K[?]1 at this temperature. Transmission electron microscopy observation showed the existence of randomly dispersed nano features that are responsible for such enhancement, some of which are similar to the nanostructures reported in the AgPbmSbTem+2 system. The origin of these regions is discussed and their influence on thermal conductivity is revealed. The results confirm the effectiveness of such a kind of nano feature in improving thermoelectric properties, especially in reducing thermal conductivity. They also indicate a new way of obtaining thermoelectric materials with such a kind of nano feature via MA and SPS. [ABSTRACT FROM AUTHOR]

High contrast ratio and high power efficiency organic light-emitting diodes (OLEDs) using a dual electron transporting layer of copper phthalocyanine (CuPc)/ titanium oxide phthalocyanine (TiOPc) as an anti-reflection layer have been investigated. The OLED configuration comprises indium tin oxide (ITO)/4,4',4?-tris{N,-(3-methylphenyl)-N-phenylamino}- triphenylamine) (m-MTDATA)/N, N'-diphenyl-N,N'-bis(l-naphthyl-phenyl)-(l,l'-biphenyl)-4, 4'-diamine (NPB)/tris(8-hydroxyquinolino)-aluminium (Alq3)/CuPc/TiOPc/LiF/Al. The contrast ratio of the device with a CuPc/TiOPc anti-reflection layer is about double and the power efficiency higher than that of a conventional device without the anti-reflection layer. The improvement in the power efficiency and the contrast ratio of the device that is obtained using a CuPc/TiOPc anti-reflection layer is attributable to the stepwise electron transporting barrier and the reduced optical reflection from the cathode. The contrast ratio suffices for outdoor display applications. [ABSTRACT FROM AUTHOR]

We propose a nonlinear ultrasonic technique by using the mixed-frequency signals excited Lamb waves to conduct micro-crack detection in thin plate structures. Simulation models of three-dimensional (3D) aluminum plates and composite laminates are established by ABAQUS software, where the aluminum plate contains buried crack and composite laminates comprises cohesive element whose thickness is zero to simulate delamination damage. The interactions between the S0 mode Lamb wave and the buried micro-cracks of various dimensions are simulated by using the finite element method. Fourier frequency spectrum analysis is applied to the received time domain signal and fundamental frequency amplitudes, and sum and difference frequencies are extracted and simulated. Simulation results indicate that nonlinear Lamb waves have different sensitivities to various crack sizes. There is a positive correlation among crack length, height, and sum and difference frequency amplitudes for an aluminum plate, with both amplitudes decreasing as crack thickness increased, i.e., nonlinear effect weakens as the micro-crack becomes thicker. The amplitudes of sum and difference frequency are positively correlated with the length and width of the zero-thickness cohesive element in the composite laminates. Furthermore, amplitude ratio change is investigated and it can be used as an effective tool to detect inner defects in thin 3D plates. [ABSTRACT FROM AUTHOR]

We report the generation of heralded single photons with Gaussian-shape temporal waveforms through the spatial light modulation technique in an atomic ensemble. Both the full width at half maximum and the peak position of the Gaussian waveform can be controlled while the single photon nature holds well. We also analyze the bandwidth of the generated single photons in frequency domain and show how the sidebands of the frequency spectrum are modified by the shape of the temporal waveform. The generated single photons are especially suited for the realization of high efficiency quantum storage based on electromagnetically induced transparency. [ABSTRACT FROM AUTHOR]

A higher-order parametric down-conversion (PDC) photon state is amazingly different from the states involving independent photon pairs. We focus on the third-order PDC photons. Firstly, we present a symmetry detector which is capable of analyzing twin-beam six-photon symmetric states in the regime of weak nonlinearities. By cascading symmetry detectors, then, it is shown that one can generate third-order PDC photons from a class of twin-beam six-photon symmetric states. Finally, as an example, we describe an application of third-order PDC photons for exploring six-mode-photon entangled states with linear optics. [ABSTRACT FROM AUTHOR]

We fabricate high quality superconductor/ferromagnet/superconductor (SFS) Josephson junctions using epitaxial NbN/Ni60Cu40/NbN trilayer heterostructures. Both experimental measurements and theoretical calculations of the ferromagnet layer thickness dependence of the Josephson critical current are performed. We observe the damped oscillation behavior of the critical current as a function of the ferromagnetic layer thickness at 4.2 K, which shows a 0–π phase transition in this type of magnetic Josephson junction. Clear 0–π and reverse π–0 phase transitions occur around the Ni60Cu40 thicknesses of 3.2 and 6.7 nm. Numerical calculations based on the quasi-classical Usadel equation and the Green function fit well with the experimental results. Compared with the dirty limit, the intermediate regime without the dead layer gives better fit for our SFS Josephson junctions because of the epitaxial structure. Both of the 0- and π-phase junctions show the ideal magnetic field dependence with a Fraunhofer-like pattern at 4.2 K. [ABSTRACT FROM AUTHOR]

Considering the non-locality of interactions in a Bose–Einstein condensate, the existence and stability of solitons subject to a -symmetric potential are discussed. In the framework of the variational approach, we investigate how the non-locality of interactions affects the self-localization and stability of a condensate with attractive two-body interactions. The results reveal that the non-locality of interactions dramatically influences the shape, width, and chemical potential of the condensate. Analytically variational computation also predicts that there exists a critical negative non-local interaction strength (pc < 0) with each fixed two-body interaction (g0 < 0), and there exists no bright soliton solution for p0 < pc. Furthermore, we study the effect of the non-locality interactions on the stability of the solitons using the Vakhitov–Kolokolov stability criterion. It is shown that for a positive non-local interaction (p0 > 0), there always exist stable bright solitons in some appropriate parameter regimes. [ABSTRACT FROM AUTHOR]

An underwater acoustic metasurface with sub-wavelength thickness is designed for acoustic wavefront manipulation. In this paper, a pentamode lattice and a frequency-independent generalized acoustic Snellʼs law are introduced to overcome the limitations of narrow bandwidth and low transmittance. The bulk modulus and effective density of each unit cell can be tuned simultaneously, which are modulated to guarantee the achievement of refractive index profile and high transmission. Here, we actualize anomalous refraction, generation of non-diffracting Bessel beam, sub-wavelength flat focusing, and surface wave conversion by constructing inhomogeneous acoustic metasurface. This design approach has potential applications in medical ultrasound imaging and underwater acoustic communications. [ABSTRACT FROM AUTHOR]

Coronal mass ejections (CMEs) often show different features in different bandpasses. By combining data in white-light (WL) and ultraviolet (UV) bands, we have applied different techniques to derive plasma temperatures, electron density, internal radial speed, and so on, within a fast CME. They serve as extensive tests of the diagnostic capabilities developed for the observations provided by future multichannel coronagraphs (such as Solar Orbiter/Metis, Chinese Advanced Space-based Solar Observatory/Lyα Solar Telescope (LST), and PROBA-3/ASPIICS). The data involved include WL images acquired by Solar and Heliospheric Observatory (SOHO)/Large Angle Spectroscopic Coronagraph (LASCO) coronagraphs, and intensities measured by the SOHO/UV Coronagraph Spectrometer (UVCS) at 2.45 R⊙ in the UV (H i Lyα and O vi 1032 Å lines) and WL channels. Data from the UVCS WL channel have been employed for the first time to measure the CME position angle with the polarization-ratio technique. Plasma electron and effective temperatures of the CME core and void are estimated by combining UV and WL data. Due to the CME expansion and the possible existence of prominence segments, the transit of the CME core results in decreases in the electron temperature down to 105 K. The front is observed as a significant dimming in the Lyα intensity, associated with a line broadening due to plasma heating and flows along the line of sight. The 2D distribution of plasma speeds within the CME body is reconstructed from LASCO images and employed to constrain the Doppler dimming of the Lyα line and simulate future CME observations by Metis and LST. [ABSTRACT FROM AUTHOR]

We investigate optimization of dichotomic local phase measurement settings for multipartite quantum systems. We first describe a method of constructing a single multipartite Bell inequality by treating the correlation function as an n-index tensor. Under a set of local phase measurement settings, we calculate the quantum prediction of the generalized Greenberger–Horne–Zeilinger state and show the exact relationship between quantum prediction and the phase factors. We show that there exists a set of optimal measurement settings relevant to maximal quantum prediction, which can contribute to testing multipartite Bell inequality in a straightforward manner. Also, we provide quantum simulation and numerical analysis with these optimal measurement settings. [ABSTRACT FROM AUTHOR]

In this work, the vertical electrical transport behavior of bilayer MoS2 under the coupling of force and light was explored by the use of conductive atomic force microscopy. We found that the current–voltage behavior across the tip–MoS2–Pt junction is a tunneling current that can be well fitted by a Simmons approximation. The transport behavior is direct tunneling at low bias and Fowler–Nordheim tunneling at high bias, and the transition voltage and tunnel barrier height are extracted. The effect of force and light on the effective band gap of the junction is investigated. Furthermore, the source–drain current drops surprisingly when we continually increase the force, and the dropping point is altered by the provided light. This mechanism is responsible for the tuning of tunneling barrier height and width by force and light. These results provide a new way to design devices that take advantage of ultrathin two-dimensional materials. Ultrashort channel length electronic components that possess tunneling current are important for establishing high-efficiency electronic and optoelectronic systems. [ABSTRACT FROM AUTHOR]

White light emitting diodes (WLEDs) based on quantum dots (QDs) are emerging as robust candidates for white light sources, however they are suffering from the problem of energy loss resulting from the re-absorption and self-absorption among the employed QDs of different peak wavelengths. It still remains a challenging task to construct WLEDs based on single-phase QD emitters. Here, CdS QDs with short synthesis times are introduced to the fabrication of WLEDs. With a short synthesis time, on one hand, CdS QDs with a small diameter with blue emission can be obtained. On the other hand, surface reconstruction barely has time to occur, and the surface is likely defect-ridden, which enables the existence of a broad emission covering the range of green, yellow and red regions. This is essential for the white light emission of CdS QDs, and is very important for WLED applications. The temporal evolution of the PL spectra for CdS QDs was obtained to investigate the influence of growth time on the luminescent properties. The CdS QDs with a growth time of 0.5 min exhibited a colour rendering index (CRI) of 79.5 and a correlated colour temperature (CCT) of 6238 K. With increasing reaction time, the colour coordinates of the CdS QDs will move away from the white light region in the CIE 1931 chromaticity diagram. By integrating the as prepared white light emission CdS QDs with a violet GaN chip, WLEDs were fabricated. The fabricated WLEDs exhibited a CRI of 87.9 and a CCT of 4619 K, which satisfy the demand of general illumination. The luminous flux and the luminous efficiency of the fabricated WLEDs, being less advanced than current commercial white light sources, can be further improved, meaning there is a need for much more in-depth studies on white light emission CdS QDs. [ABSTRACT FROM AUTHOR]

Kesterite Cu2ZnSn(SxSe1−x)4 (CZTSSe) thin films and related solar cells were successfully fabricated by a facile sol-gel method and selenization process. The influence of Polyvinylpyrrolidone (PVP) additive on the properties of the CZTSSe films and the power conversion efficiency (PCE) of the solar cells were investigated. The results reveal that the qualities of CZTSSe films can be manipulated by incorporating a small amount of PVP. With addition of 1 wt% of PVP, the smoothness and grain size of the CZTSSe films were greatly improved. The contact at the CZTSSe/Mo interface was also improved. As a result, the optimized PCE of solar cells improved from 2.24% to 4.34% after the addition of 1 wt% PVP due to the decrease of recombination at the interfaces. These results suggest that polymer addition in the precursor solution is a promising method for obtaining high quality of CZTSSe films and high-performance solar cells. [ABSTRACT FROM AUTHOR]

Melt electrospinning is a complex process, and many of the processing parameters can impact the result of fiber formation. In this paper, we conducted a systematic investigation on the impacts of the melt electrospinning parameters (including temperature, needle gauge, flow rate and collector speed) on the fiber diameter via an orthogonal design experiment. The straight single fibers were fabricated using melt electrospinning in a direct-writing way with a diameter varied from 9.68  ±  0.93 µm to 48.55  ±  3.72 µm. The results showed that the fiber diameter changed differently against different parameters: when the temperature or needle gauge increased, the fiber diameter increased first and then decreased; when the flow rate increased, the fiber diameter decreased first and then increased; when the collector speed increased, the fiber diameter decreased monotonously. We also found that the collector speed was the most influential factor while the needle gauge was least important in determining the diameter of the fiber. Moreover, the feasibility of melt electrospinning in a direct-writing way as a novel 3D printing technology had been demonstrated by fabricating both uniform and controllable structures with high accuracy, based on the optimal parameters from the orthogonal experiments. The promising results indicated that melt electrospinning can be developed as a powerful technique for fabricating miniatured parts with high resolution and controllable structures for versatile potential applications. [ABSTRACT FROM AUTHOR]

Terahertz (THz) direct detectors based on superconducting niobium nitride (NbN) hot electron bolometers (HEBs) with microwave (MW) biasing are studied. The MW is used to bias the HEB to the optimum point and to readout the impedance changes caused by the incident THz signals. Compared with the thermal biasing method, this method would be more promising in large scale array with simple readout. The used NbN HEB has an excellent performance as heterodyne detector with the double sideband noise temperature (TN) of 403 K working at 4.2 K and 0.65 THz. As a result, the noise equivalent power of 1.5 pW/Hz1/2 and the response time of 64 ps are obtained for the direct detectors based on the NbN HEBs and working at 4.2 K and 0.65 THz. [ABSTRACT FROM AUTHOR]

We investigate a one-dimensional acoustic metamaterial with a refractive index of near zero (RINZ) using an array of very thin elastic membranes located along a narrow waveguide pipe. The characteristics of the effective density, refractive index, and phase velocity of the metamaterial indicate that, at the resonant frequency , the metamaterial has zero mass density and a phase transmission that is nearly uniform. We present a mechanism for dramatic acoustic energy squeezing and anomalous acoustic transmission by connecting the metamaterial to a normal waveguide with a larger cross-section. It is shown that at a specific frequency f1, transmission enhancement and energy squeezing are achieved despite the strong geometrical mismatch between the metamaterial and the normal waveguide. Moreover, to confirm the energy transfer properties, the acoustic pressure distribution, acoustic wave reflection coefficient, and energy transmission coefficient are also calculated. These results prove that the RINZ metamaterial provides a new design method for acoustic energy squeezing, super coupling, wave front transformation, and acoustic wave filtering. [ABSTRACT FROM AUTHOR]

The searches for large-gap quantum spin Hall insulators are important for both practical and fundamental interests. In this work, we present a theoretical observation of the two-dimensional fully fluorinated stanene (SnF) by means of density functional theory. Remarkably, a significant spin-orbit coupling is observed for the SnF monolayer in the valence band at the Γ point, with a considerable indirect band gap of 278 meV. The direct gap of the SnF monolayer is at the Γ point, which is slightly larger by as much as 381 meV. In addition, the elastic modulus of the SnF monolayer is about 20 J/m2, which is comparable with the in-plane stiffness of black phosphorus monolayer along the x-direction (∼28.94 J/m2). Finally, the optical properties of stanene, SnF monolayer and stanene/SnF bilayer are calculated, in which the stanene/SnF bilayer is supposed to be an attractive sunlight absorber. [ABSTRACT FROM AUTHOR]

In this paper, a subwavelength metal-grating assisted sensor of Kretschmann style that is capable of detecting the sample with a refractive index higher than that of the substrate is proposed. The sensor configuration is similar to the traditional Kretschmann structure, but the metal film is pattered into a grating. As a TM-polarized laser beam impinges from the substrate, a resonant dip point in reflectance curve is produced at a certain incident angle. Our studies indicate that the sensing sensitivity and resolution are affected by the grating’s gap and period, and after these parameters have been optimized, a sensing sensitivity of 51.484°/RIU is obtained with a slightly changing resolution. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the effects of glycerol doping on transmittance, conductivity and surface morphology of poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate)) (PEDOT:PSS) and its influence on the performance of perovskite solar cells. . The conductivity of PEDOT:PSS is improved obviously by doping glycerol. The maximum of the conductivity is 0.89 S/cm when the doping concentration reaches 6 wt%, which increases about 127 times compared with undoped. The perovskite solar cells are fabricated with a configuration of indium tin oxide (ITO)/PEDOT:PSS/CH3NH3PbI3/PC61BM/Al, where PEDOT:PSS and PC61BM are used as hole and electron transport layers, respectively. The results show an improvement of hole charge transport as well as an increase of short-circuit current density and a reduction of series resistance, owing to the higher conductivity of the doped PEDOT:PSS. Consequently, it improves the whole performance of perovskite solar cell. The power conversion efficiency (PCE) of the device is improved from 8.57% to 11.03% under AM 1.5 G (100 mW/cm2 illumination) after the buffer layer has been modified. [ABSTRACT FROM AUTHOR]

Phononic crystal cavities with high quality (Q) factors are attractive in both signal processing and sensing applications. In this paper, 2D phononic crystal point defect cavities are fabricated on silicon slabs by micro electromechanical system (MEMS) technologies. An electrode design method is proposed to enhance displacements of the point defect modes. Then the method is applied to design MEMS resonators with different port numbers, among which Q factor as high as 21 300 is obtained in air. Multiport resonators with transmission measurements are proved to be advantageous over one-port resonators with impedance measurements in frequency resolution. A temperature insensitive resonant mass sensor is designed based on a two-port resonator. Two defect modes with strong responses in the two-port resonator are combined to compensate environmental temperature interference. The temperature compensation experiment reveals that temperature interference is effectively compensated from mass measurement and the mass sensitivity of the sensor is 5.4 Hz ng−1. The conclusion of mode selection or sensing mechanism will help to design resonators or sensors with high performances. [ABSTRACT FROM AUTHOR]

In this paper, we theoretically investigate the high-order harmonic generation and attosecond pulse generation when a two-electron He atom is exposed to the intense laser pulse. It shows that due to the two-electron double recombination mechanism, an extended plateau beyond the classical single-electron harmonic has been obtained on the two-electron harmonic spectrum. Further by using this two-electron harmonic extension scheme combined with the two-color field, two supercontinuum bandwidths with 200 eV have been obtained. As a result, a series of sub-60 as extreme ultraviolet (XUV) pulses have been directly generated. [ABSTRACT FROM AUTHOR]

The magnetic properties of two-dimensional antiferromagnet NiGa2S4 have attracted much attention and yet some problems are far from being solved. We investigate the magnetic properties of NiGa2S4 by Monte Carlo simulations. A new spin-interacting model is proposed to describe the system, and the specific heat together with the doping effect of nonmagnetic impurity is studied by simulations. The double peaks of the specific heat as well as other behaviors are well reproduced. We also compare our results with those of other models, and the underlying physics is discussed. [ABSTRACT FROM AUTHOR]

A correction to the article "Solitary wave-based strain measurements in one-dimensional granular crystals" that was published in the 2013 issue is presented.e

A correction to the article "Solitary wave-based strain measurements in one-dimensional granular crystals" that was published in July 12, 2013 issue is presented.

We have performed a detailed investigation of the molecular beam epitaxial growth and characterization of InN nanowires spontaneously formed on Si(111) substrates under nitrogen rich conditions. By employing an in situ deposited thin ([?]0.5 nm) In seeding layer prior to growth initiation, we have achieved, for the first time, non-tapered epitaxial InN nanowires, which exhibit record narrow spectral linewidths of 14 and 40 meV at 5 K and 300 K, respectively. Detailed studies confirm that the wires are nearly free of dislocations and stacking faults. The achievement of non-tapered, nearly homogeneous InN nanowires also enables, for the first time, the derivation of the band gap of InN directly from PL spectroscopy in the temperature range of 5-300 K. [ABSTRACT FROM AUTHOR]

Titania nanotube arrays (TNTA) were synthesized on a titanium substrate using anodic oxidation in an electrolyte containing ammonium fluoride and evaluated for low-temperature oxygen sensing. Their sensing properties were tested at different temperatures (50, 100, 150, 200, 250 and 300 °C) when exposed to various oxygen concentrations. The as-prepared TNTA are amorphous and exhibit much higher carrier concentration than that of annealed TNTA. Such amorphous TNTA show much higher sensitivity than that of annealed TNTA, SrTiO3 and Ga2O3 sensors. This sample demonstrates the lowest detectable oxygen concentration of 200 ppm, excellent recovery and good linear correlation at 100 °C. These results indicate that TNTA are indeed very attractive oxygen-sensing materials. [ABSTRACT FROM AUTHOR]

A nitrogen-doped titania nanotube array vertically aligned on a titanium substrate exhibits efficient electron field emission. Such a titania nanotube array shows very good stability at high field emission current (fluctuation <3% at field emission current of 160 µA within 4 h) and low turn-on and threshold fields (11.2 and 24.4 V µm[?]1, respectively) because of the coexistence of doped nitrogen and concomitant oxygen vacancies in titania nanotubes. This work demonstrates the possibility of converting pure titania nanotubes without field emission into a favorable and efficient one through the introduction of acceptor states and donor states both above the valence band maximum and below the conduction band minimum in the band gap of titania by the doped nitrogen and concomitant oxygen vacancies, respectively. Application of this doping concept to other transition metal oxides can be expected to broaden the scope of field emission materials. [ABSTRACT FROM AUTHOR]

On the basis of the complex variable moving least-square (CVMLS) approximation, a complex variable meshless local Petrov—Galerkin (CVMLPG) method is presented for transient heat conduction problems. The method is developed based on the CVMLS approximation for constructing shape functions at scattered points, and the Heaviside step function is used as a test function in each sub-domain to avoid the need for a domain integral in symmetric weak form. In the construction of the well-performed shape function, the trial function of a two-dimensional (2D) problem is formed with a one-dimensional (1D) basis function, thus improving computational efficiency. The numerical results are compared with the exact solutions of the problems and the finite element method (FEM). This comparison illustrates the accuracy as well as the capability of the CVMLPG method. [ABSTRACT FROM AUTHOR]

Pterostilbene (PTE) is known as resveratrol of the next generation and it has attracted extensive attention in recent years. PTE can inhibit the growth of a variety of tumor cells. To overcome the problem of insolubility, PTE was loaded into nanoparticles (NPs) by anti-solvent precipitation technique using soybean lecithin (SPC) and D-α-tocopheryl polyethylene glycol succinate (TPGS) as stabilizers. The obtained PTE-NPs had an average particle size of 71.0 nm, a polydispersity index （PDI） value of 0.258, and a high zeta potential of −40.8 mV. PTE-NPs can maintain particle size stability in various physiological media. The entrapment efficiency of PTE-NPs was 98.24%. And the apparently water solubility of PTE-NPs was about 53 times higher than the solubility of PTE (54.41 μg ml−1 v−1 s−1. 2.89 mg ml−1). M−1T−1T−1 assay showed that the antitumor activity of PTE-NPs on 4T1 breast cancer cells, MCF-7 breast cancer cells and Hela cervical cancer cells was significantly increased by 4, 6 and 8 times than that of free PTE, respectively. In vivo studies have shown that PTE-NPs has a certain dose dependence. When injected intraperitoneally, PTE-NPs showed a similar therapeutic effect as paclitaxel injection (TIR was 57.53% versus 57.23%) against 4T1 tumor-bearing mice. This should be due to the improved bioavailability of the drug caused by nano-drug delivery system (nano-DDS). These results indicate that PTE-NPs may be a clinically promising anti-tumor drug for breast cancer treatment. [ABSTRACT FROM AUTHOR]

A combination of large mass, weak spring and nano-grating is the key for a nano-grating accelerometer to measure nano-G acceleration. A novel compact nano-grating accelerometer integrating a large mass with nano-grating is proposed. First, the numbers of diffraction orders are calculated. Then, structure parameters are optimized by finite element analysis to achieve a high sensitivity in an ideal vibration mode. Finally, we design the fabrication method to form such a compact nano-grating accelerometer and successfully fabricate the uniform and welldesigned nano-gratings with a period of 847 nm, crater of 451nm by an FIB/SEM dual beam system. Based on the ANSYS simulation, a nano-grating accelerometer is predicted to work in the first modal and enables the accelerometer to have displacement sensitivity at 197 nm/G with a measurement range of ±1 G, corresponding to zeroth diffraction beam optical sensitivity 1%/mG. The nano-gratings fabricated are very close to those designed ones within experimental error to lay the foundation for the sequent fabrication. These results provide a theoretical basis for the design and fabrication of nano-grating accelerometers. [ABSTRACT FROM AUTHOR]

Excited states of the odd-odd nucleus 122I are investigated via the fusion-evaporation reaction 116Cd(11B,5n) at a beam energy of 68 MeV. The two most strongly populated bands in 122I are observed up to excitation energies around 10.5 MeV. Their possible configurations at lower spins are assigned to πh11/2 ... vh11/2 and πh11/2 ... vd5/2 based on the observed population, B(M1)/B(E2) values, alignments and signature splitting. E1 transitions are observed connecting the πh11/2 ... vd5/2 band to the πh11/2 ... vh11/2 band, which may be evidence of octupole collectivity. Band terminations caused by the full alignment of the valence nucleons outside the 114Sn core are observed in both bands. [ABSTRACT FROM AUTHOR]

Volatilization of Sb during the fabrication of CoSb3 by mechanical alloying and then spark plasma sintering has been successfully compensated by adding excess Sb. The average grain size increases apparently with excess Sb content, abnormally grown by about 100 times as the excess Sb is up to 4 at.%. A liquid-phase-related mechanism is used to explain the abnormal growth. The uncompensated sample shows a negative Seebeck coefficient near room temperature, while the sample compensated with 6 at.% excess Sb shows an intrinsic positive Seebeck coefficient and an enhanced ZT value, which has a maximum of about 0.1 at 350 °C, which is two times higher than the uncompensated one. The transition of electrical conductivity from n- to p-type relative to the Sb compensation is discussed in relation to the point defect. A defect equation is given to show the nature of electron generation due to Sb deficiency. The Sb-vacancy not only provides extrinsic carrier but also generates a significant impact on the band gap and hence on the Seebeck coefficient. [ABSTRACT FROM AUTHOR]

Skutterudite CoSb3polycrystalline materials were prepared using a combined process of mechanical alloying (MA) and spark plasma sintering (SPS). The influence of SPS temperature on the thermoelectric properties was focused in this work with a special emphasis on the analysis of the size effects of grains. The average grain sizes decreased from 300 to 50?nm with decreasing SPS temperatures from 600 to 300?°C. The electrical resistivities of samples spark plasma sintered at 300-600?°C all decreased with increasing temperature, indicating a classic intrinsic conduction behaviour of semiconductors. The samples spark plasma sintered at 300-500?°C showed a positive Seebeck coefficient while the sample spark plasma sintered at 600?°C showed a negative Seebeck coefficient. The room-temperature thermal conductivities were reduced from 4.30 to 2.92?W?m?1?K?1as the grain sizes were decreased from 300 to 100?nm corresponding to SPS at 600 and 400?°C, respectively. The present work indicates that MA and SPS is a good combination for fabricating fine-grained CoSb3thermoelectric materials. [ABSTRACT FROM AUTHOR]