Excitation Flux Research Articles

Sex- and age-dependent effects of androgens on glutamate-induced cell death and intracellular calcium regulation in the developing hippocampus

Hippocampal neurons must maintain control over cytosolic calcium levels, especially during development, as excitation and calcium flux are necessary for proper growth and function. But excessive calcium can lead to excitotoxic cell death. Previous work suggests that neonatal male and female hippocampal neurons regulate cytosolic calcium differently, thereby leading to differential susceptibility to excitotoxic damage. Hippocampal neurons are also exposed to gonadal hormones during development and express high levels of androgen receptors. Androgens have both neuroprotective and neurotoxic effects in adults and developing animals. The present study sought to examine the effect of androgen on cell survival after an excitatory stimulus in the developing hippocampus, and whether androgen-mediated calcium regulation was the governing mechanism. We observed that glutamate did not induce robust or sexually dimorphic apoptosis in cultured hippocampal neurons at an early neonatal time point, but did 5days later – only in males. Further, pretreatment with the androgen dihydrotestosterone (DHT) protected males from apoptosis during this time, but had no effect on females. Calcium imaging of sex-specific cultures revealed that DHT decreased the peak of intracellular calcium induced by glutamate, but only in males. To determine a possible mechanism for this androgen neuroprotection and calcium regulation, we quantified three calcium regulatory proteins, plasma membrane calcium ATPase1 (PMCA1), sodium/calcium exchanger1 (NCX1), and the sarco/endoplasmic reticulum calcium ATPase 2 (SERCA2). Surprisingly, there was no sex difference in the level of any of the three proteins. Treatment with DHT significantly decreased PMCA1 and NCX1, but increased SERCA2 protein levels in very young animals but not at a later timepoint. Taken together, these data suggest a complex interaction of sex, hormones, calcium regulation and developmental age; however androgens acting during the first week of life are implicated in regulation of hippocampal cell death and may be an underlying mechanism for sexually dimorphic apoptosis.

Modulated photocurrent experiments-comparison of different data treatments

Modulated Photocurrent experiments provide a powerful tool to characterize localized defect states within the band gap of semiconductors. However, in recent years, different data analysis methods have been established. The method proposed by Herberholz et al. identify defect positions and attempt-to-escape frequencies considering the phase shift between excitation flux and measured photo current only. In contrast, Brüggemann et al. propose to use phase shift and amplitude of the modulated photo current to resolve an energy dependent density of trap states. This work compares both analysing procedures. We demonstrate that for simple and dominant defects, such as acceptor or donor like monovalent traps, both methods give equivalent results. However, the Herberholz method fails for more complex defect arrangements as exemplified on hydrogenated amorphous silicon or polycrystalline CuInSe2.

Excitation Winding Short-Circuits in Hybrid Excitation Permanent Magnet Motor

This paper presents two short-circuit fault models of a hybrid excitation flux switching permanent magnet machine, i.e., excitation phase short-circuit and interturn short-circuit in excitation windings. Two-dimensional finite element (FE) method is used to calculate the major parameters, such as armature and excitation inductances, which are not only functions of rotor position, but also of armature and excitation currents. Moreover, in case of short-circuits, the variations of armature and excitation currents are often significant. This in turn leads to an important change in winding inductances. Therefore, in order to precisely predict machine performance under short-circuit conditions, the use of inductances versus rotor position and RMS currents is essential. With the obtained FE results, two MATLAB/Simulink-based models are established. Then, the previously mentioned short-circuits have been studied and their influences on electromagnetic performances, such as armature and excitation currents, speed and torque, armature and excitation copper losses, stator and rotor core iron losses, as well as permanent magnet (PM) eddy current losses are analyzed. Experiments have been carried out to validate the simulations.

Two-photon antenna-core oxygen probe with enhanced performance.

Recent development of two-photon phosphorescence lifetime microscopy (2PLM) of oxygen enabled first noninvasive high-resolution measurements of tissue oxygenation in vivo in 3D, providing valuable physiological information. The so far developed two-photon-enhanced phosphorescent probes comprise antenna-core constructs, in which two-photon absorbing chromophores (antenna) capture and channel excitation energy to a phosphorescent core (metalloporphyrin) via intramolecular excitation energy transfer (EET). These probes allowed demonstration of the methods’ potential; however, they suffer from a number of limitations, such as partial loss of emissivity to competing triplet state deactivation pathways (e.g., electron transfer) and suboptimal sensitivity to oxygen, thereby limiting spatial and temporal resolution of the method. Here we present a new probe, PtTCHP-C307, designed to overcome these limitations. The key improvements include significant increase in the phosphorescence quantum yield, higher efficiency of the antenna-core energy transfer, minimized quenching of the phosphorescence by electron transfer and increased signal dynamic range. For the same excitation flux, the new probe is able to produce up to 6-fold higher signal output than previously reported molecules. Performance of PtTCHP-C307 was demonstrated in vivo in pO2 measurements through the intact mouse skull into the bone marrow, where all blood cells are made from hematopoietic stem cells.

Next generation of HTS magnetic application: HTS bulk and coil interaction

The next generation of HTS magnetic bearings (SMB) will operate at magnetic field excitation higher than permanent magnets (> 1.0 T). The new bearing type is capable to support heavy -load rotors of more than one ton mass. Using FEM we calculate the interaction of HTS bulk and 2G coil to achieve higher magnetic flux excitation and flux gradients of HTS bearings at temperatures of 50 – 60 K. The new total HTS bearing type multiplies the present 10 -15 N/cm2 force density obtained with PM's by a factor of 5 and passes the force properties of active magnetic bearings (AMB). HTS coil excitation is capable to increases the levitation forces to more than the present 10 kN level and reduces relative cooling and material effort per load. We design a magnetic bearing for HTS bulk -coil excitation.

An Analytical Approach of Magnetic Diffusion in a Plate Under Time-Varying Flux Excitation

A new analytical computation of magnetic flux distribution and eddy currents is proposed in this paper. Equations are set down for a plate subjected to a time-varying flux excitation. This method consists of using Neumann's boundary conditions in the flux-density diffusion equation to consider the instantaneous variations of the imposed flux waveform. The diffusion equation is solved by separation of variables and Duhamel's theorem. Different cases of imposed magnetic flux are studied: sinusoidal flux, flux ramp, and arbitrary time-varying flux. This new analytical method is a complement of the classical approach (with Dirichlet's boundary conditions) where induction at boundary needs to be corrected to fit the instantaneous total flux. In this paper, a distinctive method allows to compute the instantaneous distributions and corresponding losses directly from the experimental flux measurements on electromagnetic devices. The analytical expressions of magnetic flux density and eddy current distributions are explicitly given. The comparison between analytical and finite-element simulation results shows the validity of the new analytical method.

Detailed photoluminescence studies of thin film Cu2S for determination of quasi-Fermi level splitting and defect levels

We have studied chalcocite (Cu2S) layers prepared by physical vapor deposition with varying deposition parameters by calibrated spectral photoluminescence (PL) and by confocal PL with lateral resolution of Δ x≈0.9 μm. Calibrated PL experiments as a function of temperature T and excitation fluxes were performed to obtain the absolute PL-yield and to calculate the splitting of the quasi-Fermi levels (QFLs) μ=Ef,n−Ef,p at an excitation flux equivalent to the AM 1.5 spectrum and the absorption coefficient α(ℏω), both in the temperature range of 20 K≤T≤400 K. The PL-spectra reveal two peaks at E#1=1.17 eV and E#2=1.3 eV. The samples show a QFL-splitting of μ>700 meV associated with a pseudo band gap of Eg=1.25 eV. The high-energy peak shows an unexpected temperature behavior, namely, an increase of PL-yield with rising temperature at variance with the behavior of QFL-splitting that decreases with rising T. Our observations indicate that, contrary to common believe, it is not the PL-yield, but rather the QFL-splitting that is the comprehensive indicator of the quality of the excited state in an illuminated semiconductor. A further examination of the lateral variation of opto-electronic properties by confocal PL and the surface contour shows no detectable correlation between Cu2S grains/grain boundaries and the PL-yield or QFL-splitting.

Reducing Cogging Force of a Permanent Magnet Transverse Flux Linear Synchronous Motor

This paper presents means to minimize the cogging force of a new type of permanent magnet excited transverse flux linear synchronous motor (PMTFLSM). The translator of this linear motor consists of cross-shaped core sets. Varying the parameters of air gap length, magnet dimensions, pole pitch and tooth width of the translator, the cogging force of the PMTFLSM will be analyzed. Taguchi's parameter method including 2D finite element analysis (FEM) is employed to minimize the cogging force. Analytical and simulation results indicate the usefulness of our approach in practice

Numerical Analysis of Influencing Factors and Capability for Thermal Wave NDT in Liquid Propellant Tank Corrosion Damage Detection

Due to the disadvantages of traditional NDT methods for liquid propellant tank corrosion detection, Thermal Wave Nondestructive Testing (ITWNDT) technology was applied. The heat exchange process of thermal wave in corrosion tank was simulated by the numerical method. Parameters of TWNDT as the best detection time (tbest), the maximum surface temperature difference (ΔTmax), and the temperature difference holding time (τΔT>0.1) were discussed as the targets. Based on these parameters, factors influencing the detection results of tank materials, dressed liquid (also considered as the corrosion product), pit characters (depth and size), heat flux and thermal excitation time length (pulsed width), environmental conditions and other factors were analyzed. Simulation results show that ITWNDT can identify the defect depth, size and position rapidly and effectively. Material properties of the tank were influencing the tbest, ΔTmax and τΔT>0.1, while the dressed liquid, thermal excitation parameters and the conditions of environment do not influence the tbest. Pit characters of the depth and size have close relationship with tbest and ΔTmax, therefore, for a tank with certain material and certain liquid dressed in, the pit corrosion damage can be accurately evaluated.

Alleviation of heat damage to photosystem II by nitric oxide in tall fescue

Nitric oxide (NO) has been found to mediate plant responses to heat stress. The objective of this study was to investigate the protective role of NO in the recovery process of photosystem II (PSII) in tall fescue (Festuca arundinacea) against heat stress. Treatment of tall fescue leaves with NO donor sodium nitroprusside significantly improved the overall behavior of PSII probed by the chlorophyll a fluorescence transients, while the inhibition of NO accumulation by 2-phenyl-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide (PTIO, a NO scavenger) plus N (G)-nitro-L-arginine-methyl ester (L-NAME, NO synthase inhibitor) dramatically disrupted the operation of PSII. Specifically, under heat stress, the exogenous NO reduced the initial fluorescence (F 0), increased the maximal quantum yield (F V/F M), and disappeared the K-step of 0.3ms. By the analysis of the JIP-test, the exogenous NO improved the quantum yield of the electron transport flux from Q A to Q B (ET0/ABS), and decreased the trapped excitation flux per reaction center (RC) (TR0/RC), electron transport flux per RC (ET0/RC), and electron flux reducing end electron acceptors per RC (RE0/RC). In addition, the exogenous NO reduced the content of H2O2, O 2 (•-) , and malondialdehyde and electrolyte leakage of tall fescue leaves. These data suggest that exogenous NO could protect plants, increase the amount of activated RC and improve the electron transport from oxygen evolving complex to D1 protein. Moreover, quantitative RT-PCR revealed that, in the presence of hydrogen peroxide, NO induced the gene expression of psbA, psbB, and psbC, which encode proteins belonging to subunits of PSII core reaction center (Psb) complex. These findings indicate that, as an important strategy to protect plants against heat stress, NO could improve the recovery process of PSII by the up regulation of the transcriptions of genes encoding PSII core proteins.

Hysteresis curves of a resistance spot welding transformer

PurposeThe aim of the paper is to provide a simple and reliable hysteresis model for prediction of magnetization curves of a resistance spot welding transformer (RSWT) core, operating in a wide range of flux densities and excitation frequencies.Design/methodology/approachThe hysteresis model considered in the paper is the T(x) description advanced by J. Takács. Three options to extend the model to the dynamic magnetization conditions are considered. The excitation conditions differ from those prescribed by international standards.FindingsThe quasi‐static Takács model combined with a fractional viscosity equation similar to that proposed by S.E. Zirka outperforms other considered options. The effect of eddy currents may be considered as a disturbance factor to the frequency‐independent quasi‐static hysteresis loop.Research limitations/implicationsThe combined approach yields in most cases a satisfactory agreement between theory and experiment. For highest frequency considered in the paper (1 kHz) excessive “heels” were observed in the modelled loops. This artifact may be reduced by the introduction of a more complicated relationship for the viscous term. Future work shall be devoted to this issue.Practical implicationsThe combined Takács‐Zirka model is a useful tool for prediction of magnetization curves of a RSWT core in a wide range of flux densities and excitation frequencies.Originality/valueThe usefulness of the Takács description has been verified in a practical application. The model is able to predict magnetization curves under non‐standard excitation conditions.

Depth resolved studies of SrTiO3 defects using x-ray excited optical luminescence and cathodoluminescence

We have performed comparative depth-dependent x-ray excited optical luminescence (XEOL) and depth resolved cathodoluminescence spectroscopy measurements in order to understand the native point defect distribution in three SrTiO3 samples. Both techniques found surface segregation of Ti3+ defects, but apparent differences in the oxygen vacancy distribution. Due to the lower excitation flux densities employed in XEOL, there is a delayed onset (“dead layer”) revealed in the oxygen defect depth distribution, which results from band bending near the surface. By modeling the data, we are able to estimate the Ti3+ depth distribution and the depletion layer width.

Spectral Calibrated and Confocal Photoluminescence of Cu2S Thin-Film Absorber

ABSTRACTWe have studied Cu2S absorber layers prepared by physical vapor deposition (PVD) by calibrated spectral photoluminescence (PL) and by confocal PL as function of temperature T and excitation fluxes to obtain the absolute PL-yield at an excitation flux equivalent to the AM1.5 spectrum and to calculate the splitting of the quasi-Fermi levels (QFL) µ = Ef,n-Ef,p and the absorption coefficient α(E), both in the temperature range 20 K ≤ T ≤ 400 K. The PL-spectra reveal two peaks at E1 = 1.17 eV and E2 = 1.3 eV, of which the low energy peak is only detectable at temperatures T < 200 K. The samples show an impressive QFL-splitting of µ > 700 meV at 300 K associated with a pseudo band gap of Eg = 1.25 eV. The high energy peak shows an unexpected temperature behavior, namely an increase of the PL-yield with rising temperature at variance with the behavior of QFL-splitting that decreases with rising T from extrapolated T = 0K value of µ = 1.3 eV. The PL-yield versus temperature will be discussed in terms of different defect states in the band gap. Our observations indicate that, contrary to common believe, it is not the PL-yield, but rather the QFL-splitting that is the comprehensive indicator of the quality of the excited state in an illuminated semiconductor. A further examination of the lateral variation of the opto-electronic properties by confocal PL shows a strong correlation between the QFL-splitting, the Urbach energy EU and the optical band gap Eopt, respectively.

Design Optimization Studies on High Torque and High Power Density Hybrid Excitation Flux Switching Motor for HEV

Abstract This paper presents design optimization studies on high torque and high power density hybrid excitation flux switching motor (HEFSM) as a candidate for traction drives in hybrid electric vehicles (HEVs). Firstly, the construction and the basic working principle of the selected HEFSM are overviewed. Then, under some design restrictions and specifications for the target HEV drives, the initial performances of the selected HEFSM are evaluated based on 2D-FEA. As the initial motor fails to achieve the target performances, design parameters are set and treated by using deterministic optimization approach. After several cycles of iteration, the target torque and power of 333Nm and 123 kW respectively, are achieved with much higher power density when compared with existing interior permanent magnet synchronous motor (IPMSM) used in HEV.

Investigation on Flux Characteristics of Field Excitation Flux Switching Machine with Single FEC Polarity

Flux switching machines (FSMs) that consist of all flux sources in the stator have been developed in recent years due to their definite advantage of single piece robust rotor structure suitable for high speed applications. They can be categorized into three groups that are permanent magnet (PM) FSM, field excitation (FE) FSM, and hybrid excitation (HE) FSM. Both PMFSM and FEFSM has only PM and field excitation coil (FEC), respectively as their main flux sources, while HEFSM combines both PM and FECs. Among these FSMs, the FEFSM offers advantages of low cost, simple construction and variable flux control capabilities suitable for various performances. In this paper, design study and flux interaction analysis of 24S-10P FEFSM with single direction of FEC winding is presented. Initially, design procedures of the FEFSM including parts drawing, materials and conditions setting, and properties setting are explained. Then, coil arrangement tests are examined to confirm the machine operating principle and position of each armature coil phase. Finally, the flux interaction between DC FEC and armature coil, FEC flux capabilities at various current condition, and initial torque are also investigated.

Development of High Torque and High Power Density Hybrid Excitation Flux Switching Motor for Traction Drive in Hybrid Electric Vehicles

This paper presents design feasibility study and development of a new hybrid excitation flux switching motor (HEFSM) as a contender for traction drives in hybrid electric vehicles (HEVs). Initially, the motor general construction, the basic working principle and the design concept of the proposed HEFSM are outlined. Then, the initial drive performances of the proposed HEFSM are evaluated based on 2D-FEA, in which the design restrictions, specifications and target performances are similar with conventional interior permanent magnet synchronous motor (IPMSM) used in HEV. Since the initial results fail to achieve the target performances, deterministic design optimization approach is used to treat several design parameters. After several cycles of optimization, the proposed motor makes it possible to obtain the target torque and power of 333 Nm and 123 kW, respectively. In addition, due to definite advantage of robust rotor structure of HEFSM, rotor mechanical stress prediction at maximum speed of 12,400 r/min is much lower than the mechanical stress in conventional IPMSM. Finally, the maximum torque and power density of the final design HEFSM are approximately 11.41 Nm/kg and 5.55 kW/kg, respectively, which is 19.98% and 58.12% more than the torque and power density in existing IPMSM for Lexus RX400h.

Impact of Rotor Pole Number on the Characteristics of Outer-rotor Hybrid Excitation Flux Switching Motor for In-wheel Drive EV

This paper present the impact of rotor pole number on the characteristics of outer-rotor hybrid excitation flux switching motor (ORHEFSM) for in-wheel drive electric vehicle (EV) applications. In recent years, researches on in-wheel motor for EV drivetrain system become more popular due to their several advantages of independent wheel controllability and higher efficiency. In addition, it provides more cabin space caused by elimination of mechanical transmission gears as conventionally use in the most of existing EV with single motor propulsion system configuration. Moreover, the proposed motor has single piece of rotor making the motor more robust and suitable for high speed applications. Under some design restrictions and specifications, design principles and initial performances of the proposed motor at various rotor pole numbers with 12 stator slots are demonstrated. Initially, the coil arrangement tests are examined to confirm the operating principle and polarity of each armature coil phase of the proposed motor. Furthermore, the profile of flux linkage, induced voltage, cogging torque and torque characteristics at various field excitation current density conditions are analyzed based on 2D- finite element analysis (FEA). The results obtained show that the appropriate combination of stator slot-rotor pole configurations are 12S-10P which initially provide highest torque and power density. Thus, by further design refinement and optimization it is expected that the motor will successfully achieved the target performances.

Comparison of Hybrid Excitation Topologies for Flux-Switching Machines

The flux-switching permanent-magnet (FSPM) machine has robust rotor structure, high reliability, high efficiency, and high torque density. The hybrid excitation topology can realize flux adjustment and good constant power operating capability of the FSPM machines. According to different combination modes of PMs, excitation winding, and iron flux bridge, this paper compares and analyzes the electromagnetic performance of different hybrid excitation flux-switching machines with particular emphasis on coupling of PM flux and electrical excitation flux, utilization ratio of excitation current, flux adjustment capability, and torque capability. The analysis conclusions are verified by finite element method and experimental results based on an investigated parallel hybrid excitation flux-switching machine.

Z-scan measurement of the nonlinear refractive index of graphene

Under strong laser illumination, few-layer graphene exhibits both a transmittance increase due to saturable absorption and a nonlinear phase shift. Here, we unambiguously distinguish these two nonlinear optical effects and identify both real and imaginary parts of the complex nonlinear refractive index of graphene. We show that graphene possesses a giant nonlinear refractive index n(2)≃10(-7) cm(2) W(-1), almost 9 orders of magnitude larger than bulk dielectrics. We find that the nonlinear refractive index decreases with increasing excitation flux but slower than the absorption. This suggests that graphene may be a very promising nonlinear medium, paving the way for graphene-based nonlinear photonics.

Multi-photon-pumped stimulated emission from ZnO nanowires: A time-resolved study

In this work, we study temporal evolution of multi-photon-pumped stimulated emission from ZnO nanowires. In addition to second harmonic generation, ultraviolet stimulated emission is observed in ZnO nanowires under femtosecond pulse excitation at 800 nm. Sharp emission peaks appear when excitation flux reaches a threshold of 80 mJ/cm2, which can be interpreted as lasing action in self-formed nanowire microcavities. Temporal evolution of the emission captured by Kerr shutter technique shows strong excitation-power dependence. The dynamic trace of stimulated emission exhibits a fast decay with a lifetime about 4.5 ps at intermediate excitation (∼100 mJ/cm2) and a lifetime about 2 ps at high excitation (>160 mJ/cm2). The difference in the lifetime can be attributed to different gain mechanisms related to excitonic interaction and electron-hole plasma, respectively.