Noise Characteristics of Optocouplers on Neutron Radiation

Neutron dose radiation experiment is designed to study the optocoupler's displacement effects and the noise characteristics. The burst noise is introduced in optocouplers on neutron radiation, which is indicated from experiments. With the increasing neutron radiation the displacement defects in space-charge region increase, the scattering enhances and the noise signal mutations increase. All these represent the noise time series mutations, the random pulses and the increasing noise complexity. The burst noise becomes evident, and the power spectrum density, the characteristic frequency and the fractal dimension of time series of noise greatly increase.     

Coverage dependence of field emission flicker noise due to lithium adsorbed on the W(112) surface

Spectral density functions of field emission current fluctuations were investigated by a probe hole technique for lithium adsorbates on the tungsten (112) surface plane in the sub- to double monolayer range. The dependence of the spectral density on the lithium surface concentration obtained slightly above room temperature, shows maxima and minima. A correspondence is found between the extrema of the coverage dependent spectral density, features of the work function, and the film structures occurring with different adparticle densities. Commensurate lithium structures are clearly manifest in the noise power.     

Properties of Josephson junctions in the inhomogeneous magnetic field of a system of ferromagnetic particles

The effect of an array of ferromagnetic nanoparticles on the field-dependent critical current of the short overlap Josephson junction is experimentally studied. Large reversible variations of the maximum critical current are observed depending on the magnetic state of the particles. The pronounced commensurability effects are detected which are proved by the additional peaks of magnetic field induced diffraction pattern.     

Measurement of noise associated with model transformer cores

The performance of a transformer core may be considered in terms of power loss and by the noise generated by the core, both of which should be minimised. This paper discusses the setting up of a suitable system for evaluation of noise in a large model transformer core (500 kV A) and issues associated with noise measurement. The equivalent continuous sound pressure level (LAeq) was used as a measure of the A-weighted sound level and measurements were made in the range 16 Hz–25 kHz for various step lap core configurations. The selection of optimum sound insulation materials between core and ground support and for enclosing the transformer is essential for minimisation of background noise. Core clamping pressure must be optimised in order to minimise noise. The use of two laminations per layer instead of one leads to an increase in noise arising from the core. Provided care is taken in building the core, good reproducibility of results can be obtained for analysis.     

Tuning of electron transport through a moebius strip: Shot noise

We study electron transport through a moebius strip attached to two metallic electrodes by the use of a Green’s function technique. A parametric approach is used based on the tight-binding model to characterize the electron transport through such a bridge system and it is observed that the transport properties are significantly affected by (a) the transverse hopping strength between the two channels and (b) the strip-to-electrodes coupling strength. In this context we also describe the noise power of the current fluctuations, which provide key information about the electron correlation which is obtained by calculating the Fano factor (F). The knowledge of these current fluctuations gives important ideas for the fabrication of efficient molecular devices.     

A semi-analytic method for computing the long-time order parameter dynamics in mean-field coupled overdamped oscillators with colored noises

The order parameter dynamics of a mean-field model is frequently investigated in macroscopic cumulant dynamics, from which a bifurcation can be predicted qualitatively. In this Letter, for quantitatively investigating the long-time order parameter dynamics, a semi-analytic method is proposed based on approximate nonlinear Fokker-Planck equations. Applying the new method to the mean-field model of periodically driven overdamped bistable oscillators with colored noise, we exhibit the bifurcation behavior and the nonlinear stochastic resonance of the order parameter by tuning noise intensity or coupling coefficient, and the accuracy of the new method are verified by direct simulation. Our observations disclose some new properties about the order parameter dynamics of the mean-field model. For example, the periodic signal shifts the critical coupling coefficient to a larger value, while the nonzero correlation time of the colored noise shifts it to a lower value. Our observation also discloses that there is no quantitatively corresponding relation between the resonant peak and the critical bifurcation parameter of the Gaussian moment system.     

Anatomy of field effects on magnetization dynamics and spin transfer noise

Spin transfer-related phenomena in nanomagnets have attracted extensive studies. In this paper we shall focus on analysis of individual and combined effects of the external, anisotropy, and demagnetization fields on magnetization dynamics and spin transfer noise. It is found that individual roles of the external, anisotropy, and demagnetization fields, as well as the combined roles of external plus anisotropy fields and anisotropy plus demagnetization fields, do not change the behavior of current induced magnetization switching. Such magnetization reversal procedures are of low noise. Our dynamics and power spectral density calculations show that it is the demagnetization field that plays a major role in inducing spin transfer noise: the demagnetization field itself or in combination with the anisotropy field will result in wave-like switching; moreover, the demagnetization field, together with the external field (not too small), will lead to precession and hence the system would be in noisy states. Our modeling work for an elliptical Py alloy is qualitatively consistent with Cornell's experiment and simulation [Science 307 (2005) 228].     

Influence of the Nonlinearity of Loudspeakers on the Performance of Thermoacoustic Refrigerators Driven by Current and Voltage

The influence of the nonlinearity of electrodynamic loudspeakers on the performance of thermoacoustic refrigerators with the loudspeakers as acoustic sources is studied by nonlinear equivalent circuit models of electrodynamic loudspeakers driven by current and voltage. The simulated results demonstrate that there are different nonlinear effects between current-drive and voltage-drive refrigerators, and the differences are mainly induced by the motional electromotive force caused by the coil moving in the magnetic field. With voltage driving, the influence of the nonlinearity of the loudspeaker on the diaphragm displacement and acoustic output power is much smaller than that with current driving. Therefore, considering the nonlinearity of the loudspeakers, a proper driving method must be chosen according to the practical applications although little difference is found with the linear models.     

Current-influenced voltage noise in bulk polycrystalline high-Tc superconductors

The 1/f voltage noise in bulk polycrystalline high-temperature superconductors (HTSC) under bias current and magnetic field has its origin in the noise current-dependence of the grain boundary junctions (GBJs), due in turn to the correlated effects of junction critical current and normal resistance fluctuations. The analogy between the results obtained by varying the bias current through the specimen and those performed with temperature as variable is evidenced. The noise maxima obtained in both sets of measurements turn out to be caused by the junction critical current fluctuations, which dominate when the currents flowing through the GBJs are close to the Josephson critical current. The anti-phase correlation between the normal resistance and the critical current fluctuations is responsible for the monotonical decrease of the noise at constant bias current, with the temperature exceeding the value corresponding to the noise maximum. In contrast, varying the bias current at fixed temperature, the voltage noise exhibits a local minimum followed by an increasing tendency after passing through the maximum.     

Correlation between changes in pinning strength and flux flow noise due to annealing in a type II superconductor

Correlations are observed between reductions in the critical current and the superconducting flux flow noise power as a deformed Pb₈₀In₂₀ foil undergoes room temperature annealing, thus providing evidence that the noise originates from local interactions between moving fluxoids and pinning centers.     

Effect of cobalt-60 gamma irradiation on graphene: Raman and field emission investigations

Electrophoretically deposited graphene (HG) on silicon is irradiated using a cobalt-60 gamma radiation source with the radiation dose up to 22.7 kGy. The effect of gamma irradiation on the field emission current noise behavior of HG is investigated. The power spectra of pristine and irradiated HG exhibit 1/f^α type of noise, with α ～ 0.8. The magnitude of noise power is observed to increase with the radiation dose. The variations in the turn on field and noise power in the emission current are attributed to the structural modifications of HG, as revealed from the field emission scanning electron microscopic and Raman spectroscopic studies.     

A New Discharge Scheme of a Prepulse Plus Two Main Pulses for Capillary-Discharge Soft-X-Ray Laser

Reducing the capillary-discharge current is one way of possibly decreasing the pumping power requirement. We examine the influence of various discharge currents on laser intensity and determine the suitable pre-discharge condition for a 46.9-nm discharge-pumped Ne-like Ar soft-x-ray amplifier. The experimental results show that a high additional pre-pulse current at amplitude of several kA and with a very short duration of several tens of nanosecond can effectively decrease the amplitude of the main discharge current at the lasing time. We propose a new discharge scheme of a pre~pulse plus two main pulses which appears to significantly decrease the requirement for discharge current. This in turn may decrease the pumping power requirement for the capillary discharge laser and can greatly increase laser efficiency.     

f-γ current fluctuations in organic semiconductors: evidence for percolation

The f^-γ sloped current noise power spectra, observed in organic semiconductors, have been interpreted within a variable range hopping mechanism of the fluctuations. The relative current noise power spectral density exhibits a maximum at the trap-filling transition between the ohmic and the space-charge-limited-current regime [Phys. Rev. Lett. 95, 236601 (2005)]. Here, we discuss the electronic conditions determining the crossover from ohmic to space-charge-limited transport. These arguments shed light on the need to adopt a percolative fluctuation picture to account for the competition between insulating and conductive phases coexisting at the transition, where small changes in the external bias lead to dramatic effects in the fluctuations.     

Applications of impact-ionization metal–oxide-semiconductor (I-MOS) devices to circuit design

In this paper, the applicability of impact-ionization metal–oxide-semiconductor (I-MOS) devices has been discussed to some circuits such as static inverters, static NAND gates, static NOR gates, and 6T-SRAM cells. Based on detailed circuit analysis, some critical issues are overcome: cascadability, power consumption, series connection, and unidirectional output current. Complementary I-MOS (CI-MOS) inverters show higher noise margin and lower crowbar current than CMOS ones, which leads to the reduction of supply voltage and short-circuit power dissipation, respectively. In the case of static NAND and NOR gates, the CI-MOS also shows improved noise margin. Finally, CI-MOS 6T-SRAM cells show 22.6% improvement in SNM without much penalty in cell area compared with CMOS ones.     

Freezing transition in the mean-field approximation model of pedestrian counter flow

We study the freezing transition in the counter flow of pedestrians within the channel numerically and analytically. We present the mean-field approximation (MFA) model for the pedestrian counter flow. The model is described in terms of a couple of nonlinear difference equations. The excluded-volume effect and bi-directionality are taken into account. The fundamental diagrams (current-density diagrams) are derived. When pedestrian density is higher than a critical value, the dynamical phase transition occurs from the free flow to the freezing (stopping) state. The critical density is derived by using the linear stability analysis. Also, the velocity and current (flow) at the steady state are derived analytically. The analytical result is consistent with that obtained by the numerical simulation.     

Berry phase and shot noise for spin-polarized and entangled electrons

Shot noise for entangled and spin-polarized states in a four-probe geometric setup has been studied by adding two rotating magnetic fields in an incoming channel. Our results show that the noise power oscillates as the magnetic fields vary. The singlet, entangled triplet and polarized states can be distinguished by adjusting the magnetic fields. The Berry phase can be derived by measuring the shot noise power.     

Stochastic Resonance in Neural Systems with Small-World Connections

We study the stochastic resonance （SR） in Hodgkin-Huxley （HH） neural systems with small-world （SW） connections under the noise synaptic current and periodic stimulus, focusing on the dependence of properties of SR on coupling strength c. It is found that there exists a critical coupling strength c^＊ such that if c 〈 c^＊, then the SR can appear on the SW neural network. Especially, dependence of the critical coupling strength c^＊ on the number of neurons N shows the monotonic even almost linear increase of c^＊ as N increases and c^＊ on the SW network is smaller than that on the random network. For the effect of the SW network on the phenomenon of SR, we show that decreasing the connection-rewiring probability p of the network topology leads to an enhancement of SR. This indicates that the SR on the SW network is more prominent than that on the random network （p = 1.0）. In addition, it is noted that the effect becomes remarkable as coupling strength increases. Moreover, it is found that the SR weakens but resonance range becomes wider with the increase of c on the SW neural network.     

Wide bandwidth phase-locked diode laser with an intra-cavity electro-optic modulator

Two extended cavity laser diodes are phase-locked, thanks to an intra-cavity electro-optical modulator. The phase-locked loop bandwidth is on the order of 10 MHz, which is about twice larger than when the feedback correction is applied on the laser current. The phase noise reaches −120 dBrad²/Hz at 10 kHz. This new scheme reduces the residual laser phase noise, which constitutes one of the dominant contributions in the sensitivity limit of atom interferometers using two-photon transitions.     

Metastable state of sliding CDW in K0.3MoO3

The narrow band noise and the transient voltage oscillation were investigated in a k_0.3MoO₃ sample, which showed different I–V characteristics in the non-linear conductivity region for dc and pulse methods. For repeated current pulses, after a sufficiently long duration of dc current, the voltage response showed relaxation behavior with a relaxation time of about 30 min at 77 K. Similar relaxation was also observed for the opposite case of a dc current applied after repeated pulses. The slope of frequency of voltage oscillation against CDW current was constant through these relaxation process in both dc and pulse cases. But the peak of narrow band noise is larger and sharper after repeated pulses than in the dc stationary state. This result was understood as an enhancement of the coherent-phase region for voltage oscillation in the case of repeated pulses.     

Electronic properties of Z-shaped graphene nanoribbon under uniaxial strain

Based on tight-binding approximation and a generalized Green's function method, the effect of uniaxial strain on the electron transport properties of Z-shaped graphene nanoribbon (GNR) composed of an armchair GNR sandwiched between two semi-infinite metallic armchair GNR electrodes is numerically investigated. Our results show that the increase of uniaxial strain enhances the band gap and leads to a metal-to-semiconductor transition for Z-shaped GNR. Furthermore, in the Landauer–Büttiker formalism, the current–voltage characteristics, the noise power resulting from the current fluctuations and Fano factor of strained Z-shaped GNR are explored. It is found the threshold voltage for the current and the noise power increased so that with reinforcement of the uniaxial strain parameter strength, the noise power goes from the Poisson limit to sub-Poisson region at higher bias voltages.