Enhancement factor K0, which characterizes NMR and EPR frequency shifts for Cs-129Xe, is measured for the first time. The enhancement factor r-o was measured to be (702±41) at 80 ℃ and (653±20) at 90 ℃, using the NMR frequency shift, detected by atomic magnetometer at a low magnetic field of 100 nT. This result is useful for predicting the EPR frequency shifts for Cs and the NMR frequency shifts for 129Xe in spin-exchange cells. 相似文献
Two different methods to model a point absorber wave energy converter(WEC)with direct drive linear power take-off(PTO)are proposed in the present study:the frequency domain(FD)method and the time domain(TD)method.In the FD analysis,the frequency response function(FRF)of the WEC device is obtained via the equation of motion,and the expressions of power capture width in regular and random waves are derived as well.In the TD modeling,based on a state space approximation of the convolution term in the motion equation,both regular wave and random wave simulations are carried out.The regular wave simulation results indicate that the state space approximation is sufficiently accurate and the capture width reaches the maximum in the vicinity of the natural frequency.In the random wave simulations,the effects of buoy size,the PTO damping and wave climate on the power capture width are discussed in detail,which leads to the conclusion that the capture widths are influenced by the natural frequency of the WEC device,peak frequency of the wave spectrum,the amplitude of FRF and PTO damping.Furthermore,the increase of the capture width is at the cost of a relatively large buoy size and PTO damping when control is not included. 相似文献
Pentacene thin‐film transistor with high‐κ TaLaO as gate dielectric has been fabricated and shows a carrier mobility of 0.73 cm2/V s, much higher than that based on pure La2O3 (0.43 cm2/V s) due to the smoother surface of the TaLaO film and thus larger pentacene islands grown on it in the initial stage. Moreover, among various times for fluorine‐plasma treatment on the TaLaO gate dielectric, 100 seconds result in the highest carrier mobility of 1.12 cm2/V s due to (1) smoothest oxide surface achieved by fluorine passivation of oxide traps, as measured by AFM and supported by smallest sub‐threshold swing and lowest low‐frequency noise; (2) the largest pentacene grains grown on the smoothest oxide surface, as demonstrated by AFM.
The discovery of a novel phase‐locked frequency comb generated from a monolithic laser with the concurrent processes of self‐mode locking (SML) and stimulated Raman scattering (SRS) is reported. It is experimentally shown that the width of the Raman gain can be exploited to considerably expand the frequency comb of a monolithic SML crystal laser via the SRS process. At a pump power of 6.5 W, an output power of 140 mW in the Stokes wave with a pulse width as narrow as 2.9 ps at a pulse repetition rate of 6.615 GHz is obtained. The present finding not only provides useful insights into the monolithic intracavity SRS process but also paves the way for generating mode‐locked pulses based on monolithic self‐Raman crystals. 相似文献
Conventional numerical techniques, used to study the acoustics of a car passenger cabin, treat the cabin as an isolated cavity excited by the cavity boundaries. Realistically, other cavity volumes such as the trunk communicate with the cabin through the holes in the parcel shelf of the car. An extended acoustic model of a car is formed by the cavity volumes of the passenger compartment and the trunk as well as air leakages through the holes provided for electrical devices and ventilation on the parcel shelf. In this study, the dynamic influence of air leakages between the passenger and trunk compartments on the first and second coupled system modes was investigated experimentally using acoustic frequency response function. The response to the acoustic excitation was measured for four different configurations of trim and holes of the parcel shelf. The natural frequencies of the first and second coupled system modes increased with increasing holes size with and without the trim of the parcel shelf. The experimental results were in good agreement with the reported results of coupling effects of double cavities connected by a neck. In the low frequency region since the wavelength is longer compared to the holes dimension, these holes act as point sources. 相似文献
Centrifugal pumps are a source of pressure and flow rate perturbations in hydraulic pumping systems. In particular, a significant excitation is usually induced at the blade-passing frequency and harmonics as a consequence of the fluid-dynamic interaction between the rotor and the stator. The magnitude of this excitation is very dependent on the internal geometry of the pump and on its point of operation, but it depends also on the acoustic response of the hydraulic network to the perturbations. The induced and transmitted perturbations can be either amplified or reduced depending on the pump-circuit acoustic coupling, and thus they can lead to excessive levels of noise and vibration under certain conditions. The purpose of the present investigation is the theoretical and experimental characterization of the perturbations induced in a laboratory pumping system, as a function of the acoustic impedance of the pipelines. For different points of operation, the blade-passing frequency impedance is changed by varying the speed of rotation and, additionally, by modifying a closed side branch of the hydraulic system (that is, in the absence of net flow through it). For the theoretical calculations an acoustic model, based on matrix formulation, is applied to obtain the influence of different acoustic impedances of the suction side on the pressure fluctuations at the pump. Test measurements with a fast-response piezoelectric pressure transducer situated at the tongue region of the pump under the same system configurations confirm the significant effect of the pump-circuit acoustic coupling on the pressure perturbations. 相似文献
Active cancellation stealth is a smart signal blanking method, that it has become an important developing direction on modern stealth technology. In order to further explore the active cancellation stealth technology, we are considering the detection and cancellation of receiving/transmitting antenna pattern is different. Put forward active cancellation system simulation structure diagram based on MATLAB/SIMULINK, where the phased array radar system as the modelling object, and established the active cancellation stealth system mathematical model based on digital radio frequency memory (DRFM) and the radar signal processing system of the coherent video simulation model, based on linear frequency modulation and radar coherent pulse signal simulation, verified the rationality and validity of the design, as the active cancellation stealth engineering technology laid the foundation. 相似文献
In this paper, we derive the time dependent solution of the effective master equation for the reduced density matrix operator of a two level atom driven by a coherent laser field and damped by a finite bandwidth squeezed vacuum. The results show that the initial state setting, detuning parameter and Rabi frequency play important roles in the evolution of the system dynamics and geometric phase. We present a useful way for controlling the geometric phase variation for the system under consideration. 相似文献
Two-level injection-locked opto-electronic oscillator is proposed for low phase noise. Dielectric resonator oscillator (DRO) is used as the first injection source, injection locking a long-fiber loop based opto-electronic oscillator, then its output is injection locking another long-fiber opto-electronic oscillator for getting a lower-phase noise output carrier. After the first injection, the single side band (SSB) phase noise at 10 kHz offset frequency decreases from −123 dBc/Hz to −135 dBc/Hz, then through the second injection the SSB phase noise drops down to −146 dBc/Hz. 相似文献