Structural control of magnetic nanoparticles for positive nuclear magnetic resonance imaging

In addition to the tens of millions of medical doses consumed annually around the world,a vast number of nuclear magnetic resonance imaging(MRI)contrast agents are being deployed in MRI research and development,offering precise diagnostic information,targeting capabilities,and analyte sensing.Superparamagnetic iron oxide nanoparticles(SPIONs)are notable among these agents,providing effective and versatile MRI applications while also being heavy-metal-free,bioconjugatable,and theranostic.We designed and implemented a novel two-pronged computational and experimental strategy to meet the demand for the efficient and rigorous development of SPION-based MRI agents.Our MATLAB-based modeling simulation and magnetic characterization revealed that extremely small maghemite SPIONs in the 1-3 nm range possess significantly reduced transversal relaxation rates(R_(2))and are therefore preferred for positive(T_(1)-weighted)MRI.Moreover,X-ray diffraction and X-ray absorption fine structure analyses demonstrated that the diffraction pattern and radial distribution function of our SPIONs matched those of the targeted maghemite crystals.In addition,simulations of the X-ray near-edge structure spectra indicated that our synthesized SPIONs,even at 1 nm,maintained a spherical structure.Furthermore,in vitro and in vivo MRI investigations showed that our 1-nm SPIONs effectively highlighted whole-body blood vessels and major organs in mice and could be cleared through the kidney route to minimize potential post-imaging side effects.Overall,our innovative approach enabled a swift discovery of the desired SPION structure,followed by targeted synthesis,synchrotron radiation spectroscopic studies,and MRI evaluations.The efficient and rigorous development of our high-performance SPIONs can set the stage for a computational and experimental platform for the development of future MRI agents.

A low-noise X-band microwave source with digital automatic frequency control for electron paramagnetic resonance spectroscopy

We report a new design of microwave source for X-band electron paramagnetic resonance spectrometer.The microwave source is equipped with a digital automatic frequency control circuit.The parameters of the digital automatic frequency control circuit can be flexibly configured for different experimental conditions,such as the input powers or the quality factors of the resonator.The configurability makes the microwave source universally compatible and greatly extends its application.To demonstrate the ability of adapting to various experimental conditions,the microwave source is tested by varying the input powers and the quality factors of the resonator.A satisfactory phase noise as low as-135 d Bc/Hz at 100-k Hz offset from the center frequency is achieved,due to the use of a phase-locked dielectric resonator oscillator and a direct digital synthesizer.Continuous-wave electron paramagnetic resonance experiments are conducted to examine the performance of the microwave source.The outstanding performance shows a prospect of wide applications of the microwave source in numerous fields of science.

Adaptive rotor current control for wind-turbine driven DFIG using resonant controllers in a rotor rotating reference frame

This paper proposes an adaptive rotor current controller for doubly-fed induction generator (DFIG), which consists of a proportional (P) controller and two harmonic resonant (R) controllers implemented in the rotor rotating reference frame. The two resonant controllers are tuned at slip frequencies ωslip+ and ωslip-, respectively. As a result, the positive- and negative-sequence components of the rotor current are fully regulated by the PR controller without involving the positive- and negative-sequence decomposition, which in effect improves the fault ride-through (FRT) capability of the DFIG-based wind power generation system during the period of large transient grid voltage unbalance. Correctness of the theoretical analysis and feasibility of the proposed unbalanced control scheme are validated by simulation on a 1.5-MW DFIG wind power generation system.

A Novel Resonant Frequency Tracking Control for Linear Compressor Based on MRAS Method

To optimize the efficiency of the linear compressor,its operating frequency must be controlled equal to the system resonant frequency.The traditional resonant frequency tracking control algorithm relies on the steady state characteristics of the system,which suffers from slow convergence speed,low accuracy and slow system response.In order to solve these problems,a novel resonant frequency tracking control for linear compressor based on model reference adaptive system(MRAS)is proposed in this paper,and the parameter adaptive rate is derived by the Popov's hyperstability theory,so that the system resonant frequency can be directly calculated through the parameter adaptive rate.Furthermore,the traditional algorithm needs to calculate the piston stroke signal by integrating the back-EMF,which has the problem of integral drift.The algorithm proposed in this paper only needs the velocity signal,and the accuracy of the velocity calculation can be ensured by utilizing the self-adaptive band-pass filter(SABPF),thereby greatly improving the accuracy of the resonance frequency calculation.Simulation results verify the effectiveness of the proposed algorithm.

Bandgap adjustment of a sandwich-like acoustic metamaterial plate with a frequency-displacement feedback control method

Several types of acoustic metamaterials composed of resonant units have been developed to achieve low-frequency bandgaps.In most of these structures,bandgaps are determined by their geometric configurations and material properties.This paper presents a frequency-displacement feedback control method for vibration suppression in a sandwich-like acoustic metamaterial plate.The band structure is theoretically derived using the Hamilton principle and validated by comparing the theoretical calculation results with the finite element simulation results.In this method,the feedback voltage is related to the displacement of a resonator and the excitation frequency.By applying a feedback voltage on the piezoelectric fiber-reinforced composite(PFRC)layers attached to a cantilever-mass resonator,the natural frequency of the resonator can be adjusted.It ensures that the bandgap moves in a frequency-dependent manner to keep the excitation frequency within the bandgap.Based on this frequency-displacement feedback control strategy,the bandgap of the metamaterial plate can be effectively adjusted,and the vibration of the metamaterial plate can be significantly suppressed.

Performance enhancement of a viscoelastic bistable energy harvester using time-delayed feedback control

This paper focuses on the stochastic analysis of a viscoelastic bistable energy harvesting system under colored noise and harmonic excitation, and adopts the time-delayed feedback control to improve its harvesting efficiency. Firstly, to obtain the dimensionless governing equation of the system, the original bistable system is approximated as a system without viscoelastic term by using the stochastic averaging method of energy envelope, and then is further decoupled to derive an equivalent system. The credibility of the proposed method is validated by contrasting the consistency between the numerical and the analytical results of the equivalent system under different noise conditions. The influence of system parameters on average output power is analyzed, and the control effect of the time-delayed feedback control on system performance is compared. The output performance of the system is improved with the occurrence of stochastic resonance(SR). Therefore, the signal-to-noise ratio expression for measuring SR is derived, and the dependence of its SR behavior on different parameters is explored.

Performance Analysis of PI and Fuzzy Control for Modified LCC Resonant Converter Incorporating Boost Converter

In this paper, the modified LCC type of series-parallel Resonant Converter (RC) was designed and state-space modeling analysis was implemented. In this proposed converter, one leg of full bridge diode rectifier is replaced with Synchronous Rectifier (SR) switches. The proposed LCC converter is controlled using frequency modulation in the nominal state. During hold-up time, the SRswitches control is changed from in-phase to phase-shifted gate signal to obtain high DC voltage conversion ratio. Furthermore, the closed loop PI and fuzzy provide control on the output side without decreasing the switching frequency. The parameter such as conduction loss on primary and secondary side, switching loss, core and copper also reduced. Simultaneously, the efficiency is increased about 94.79 is realized by this scheme. The proposed converter with an input of 40 V is built to produce an output of 235 V with the help of ZVS boost converter [1] even under line and load disturbances. As a comparison, the closed loop fuzzy controller performance is feasible and less sensitive than PI controller.

Active Current Sharing of LCLC Resonant Converter with Switch-Controlled-Capacitor Technology

In this paper,an interleaved LCLC converter with enhancement-mode(E-mode)GaN devices is introduced to achieve the accurate current sharing performance for data center applications. Any tolerance in the resonant tank elements can lead to large load imbalance between any two different phases. Due to the steep gain curves of LCLC converters,conventional current sharing methods are not effective. In the proposed converter,the impedances of the resonant networks are matched by switching a capacitor,i.e.,switch controlled capacitor(SCC),in series with the resonant capacitor in one or some of the phases,which results in accurate load current sharing among the phases with an accuracy around 0.025%. The load share of a phase is sensed through the resonant current on it,and the control logic applied to such current sharing can be achieved. By this method,accurate current sharing is achieved for a wide input voltage range required for the hold-up time in data center applications. Interleaving is applied in the proposed multiphase LCLC converter,resulting in low current stress on the output capacitor and allowing ceramic capacitor implementation. Moreover,phase shedding accomplishes high light load efficiency. The performance of the proposed interleaved LCLC converter is verified by a two-phase 1 k W prototype with an input voltage ranging from 250 V to 400 V and a fixed 12 V output voltage.

Fuzzy Logic Controlled Dual Active Bridge Series Resonant Converter for DC Smart Grid Application

Over the last few years, smart grids have become a topic of intensive research, development and deployment across the world. This is due to the fact that, through the smart grid, stable and reliable power systems can be achieved. This paper presents a fuzzy logic control for dual active bridge series resonant converters for DC smart grid application. The DC smart grid consists of wind turbine and photovoltaic generators, controllable and DC loads, and power converters. The proposed control method has been applied to the controllable load＇s and the grid side＇s dual active bridge series resonant converters for attaining control of the power system. It has been used for management of controllable load＇s state of charge, DC feeder＇s voltage stability during the loads and power variations from wind energy and photovoltaic generation and power flow management between the grid side and the DC smart grid. The effectiveness of the proposed DC smart grid operation has been verified by simulation results obtained by using MATLAB and PLECS cards.

The Mechanism of Eliminating Harmonic Resonance with Controllers and Application to the Power Systems

The phenomenon of anti-symmetrical bifurcation of periodic solutionsoccurring near an integral manifold is the intrinsic cause resulting in harmonic resonanceover-voltage in power systems. Due to this discovery, the principle of eliminating resonance byusing anti-bifurcation technique is presented, which makes that the theoretical bases of verymeasure to eliminate resonance are unified firstly from a point of view of basic theory. Ourdiscussion models depend on a class of nonlinear control model. Using the direct Lyapunov method, acomplete theoretical proof is given in accordance with the measure of eliminating resonance byconnecting nonlinear resistor in series to the neutral point of P. T., and the feedback control lawbeing applied. It comprises the action of parameters of resistor to eliminate resonance and theactual process of eliminating resonance, i.e., to go against bifurcation process which forces thebig harmonic solutions to retreat to the integral manifold gradually and disappear eventually, whichby using the nonlinear controllers. This makes it sure that the intrinsic cause of resonance iseliminated thoroughly. The obtained theory results and computing results are better than thepresented results.

Research on Rugged Resonant DC Link Soft-Switching Static Inverter

A novel resonant dc link soft switching static inverter topology is presented. The soft switching operation principle and pulse width modulation control feature of dc link is analyzed in detail. The discrete pulse control strategy of inverter bridge is discussed. The operation characteristics of inverter are analyzed and verified by experiment.

Adaptive Control of Helicopter Ground Resonance with Magnetorheological Damper

The methodology for adaptive control of helicopter ground resonance with magnetorheological （MR） damper is presented. The adaptive inverse control method is used to control the output damping force of MR damper and the range of the damping force is given. Through the adaptive inverse control, the damping force of MR damper is fit to a desired damping force. With the background of applying MR damper to control of helicopter ground resonance, a model of loss force and an adaptive arithmetic for stabilization of the coupled rotor/fuselage system are presented. The simulation shows that the controller presented in this paper can stabilize the rotor/fuselage coupling system quickly and control the helicopter ground resonance effectively.

Optimal Delayed Control of Nonlinear Vibration Resonances of Single Degree of Freedom System

The primary resonance of a single-degree-of-freedom(SDOF)system subjected to a harmonic excitation is mitigated by the method of optimal time-delay feedback control.The stable regions of the time delays and feedback gains are obtained from the stable conditions of eigenvalue equation.Attenuation ratio is applied for evaluating the performance of the vibration control by taking aproportion of peak amplitude of primary resonance for the suspension system with or without controllers.Taking the attenuation ratio as the objective function and the stable regions of the time delays and feedback gains as constrains,the optimal feedback gains are determined by using minimum optimal method.Finally,simulation examples are also presented.

Bifurcation control of nonlinear oscillator in primary and secondary resonance

A weakly nonlinear oscillator was modeled by a sort of differential equation, a saddle-node bifurcation was found in case of primary and secondary resonance. To control the jumping phenomena and the unstable region of the nonlinear oscillator, feedback controllers were designed. Bifurcation control equations were obtained by using the multiple scales method. And through the numerical analysis, good controller could be obtained by changing the feedback control gain. Then a feasible way of further research of saddle-node bifurcation was provided. Finally, an example shows that the feedback control method applied to the hanging bridge system of gas turbine is doable.

Wave propagation control in periodic track structure through local resonance mechanism

Excessive vibration and noise radiation of the track structure can be caused by the operation of high speed trains.Though the track structure is characterized by obvious periodic properties and band gaps,the bandwidth is narrow and the elastic wave attenuation capability within the band gap is weak.In order to effectively control the vibration and noise of track structure,the local resonance mechanism is introduced to broaden the band gap and realize wave propagation control.The locally resonant units are attached periodically on the rail,forming a new locally resonant phononic crystal structure.Then the tuning of the elastic wave band gaps of track structure is discussed,and the formation mechanism of the band gap is explicated.The research results show that a new wide and adjustable locally resonant band gap is formed after the resonant units are introduced.The phenomenon of coupling and transition can be observed between the new locally resonant band gap and the original band gap of the periodic track structure with the band gap width reaching the maximum at the coupling position.The broader band gap can be applied for vibration and noise reduction in high speed railway track structure.

New botanical drug, HL tablet, reduces hepatic fat as measured by magnetic resonance spectroscopy in patients with nonalcoholic fatty liver disease: A placebo-controlled, randomized, phase Ⅱ trial

AIM To evaluate the efficacy and safety of HL tablet extracted from magnolia officinalis for treating patients with nonalcoholic fatty liver disease(NAFLD).METHODS Seventy-four patients with NAFLD diagnosed by ultrasonography were randomly assigned to 3 groups given high dose(400 mg) HL tablet, low dose(133.4 mg) HL tablet and placebo, respectively, daily for 12 wk. The primary endpoint was post-treatment change of hepatic fat content(HFC) measured by magnetic resonance spectroscopy. Secondary endpoints included changes of serum aspartate aminotransferase, alanine aminotransferase(ALT), cholesterol, triglyceride, free fatty acid, homeostasis model assessment-estimated insulin resistance, and body mass index(BMI).RESULTS The mean HFC of the high dose HL group, but not of the low dose group, declined significantly after 12 wk of treatment(high dose vs placebo, P = 0.033; low dose vs placebo, P = 0.386). The mean changes of HFC from baseline at week 12 were-1.7% ± 3.1% in the high dose group(P = 0.018),-1.21% ± 4.97% in the low dose group(P = 0.254) and 0.61% ± 3.87% in the placebo group(relative changes compared to baseline, high dose were:-12.1% ± 23.5%, low dose:-3.2% ± 32.0%, and placebo: 7.6% ± 44.0%). Serum ALT levels also tended to decrease in the groups receiving HL tablet while other factors were unaffected. There were no moderate or severe treatment-related safety issues during the study.CONCLUSION HL tablet is effective in reducing HFC without any negative lipid profiles, BMI changes and adverse effects.

Control of stochastic resonance in bistable systems by using periodic signals

According to the characteristic structure of double wells in bistable systems, this paper analyses stochastic fluctuations in the single potential well and probability transitions between the two potential wells and proposes a method of controlling stochastic resonance by using a periodic signal. Results of theoretical analysis and numerical simulation show that the phenomenon of stochastic resonance happens when the time scales of the periodic signal and the noise-induced probability transitions between the two potential wells achieve stochastic synchronization. By adding a bistable system with a controllable periodic signal, fluctuations in the single potential well can be effectively controlled, thus affecting the probability transitions between the two potential wells. In this way, an effective control can be achieved which allows one to either enhance or realize stochastic resonance.

A review of nuclear magnetic resonance(NMR) technology applied in the characterization of polymer gels for petroleum reservoir conformance control

Polymer gel systems have been widely applied to control excessive water and improve oil recovery(IOR)in petroleum reservoirs.They are usually divided into two main types,in-situ cross-linked polymer gels,and pre-formed polymer gels.In recent years,nuclear magnetic resonance(NMR) technology has been gradually applied to the research of polymer gel systems due to its unique analysis advantages.This paper is intent to review these works systematically.For in-situ cross-linked polymer gel systems,NMR can be used to characterize the chemical structure changes of the polymer,the cross-linker,and the auxiliary agent in the formulation of the polymer gel systems.Moreover,the gelation time and the gel strength of the in-situ cross-linked polymer gel systems can also be measured by NMR.For pre-formed polymer gels,NMR can be employed to detect the chemical structure of the designed products.Last,the NMR method can evaluate the plugging,water control,and oil improvement performance of the polymer gels in porous media without using dopants.This review can help readers build a more systematic understanding of the application of NMR technology in polymer gel systems for IOR and help re searchers to more deeply study the performance of polymer gel systems.

Oil Production Optimization by Means of a Combined“Plugging,Profile Control,and Flooding”Treatment:Analysis of Results Obtained Using Computer Tomography and Nuclear Magnetic Resonance

Due to long-term water injection,often oilfields enter the so-called medium and high water cut stage,and it is difficult to achieve good oil recovery and water reduction through standard methods(single profile control and flooding measures).Therefore,in this study,a novel method based on“plugging,profile control,and flooding”being implemented at the same time is proposed.To assess the performances of this approach,physical simulations,computer tomography,and nuclear magnetic resonance are used.The results show that the combination of a gel plugging agent,a polymer microsphere flooding agent,and a high-efficiency oil displacement agent leads to better results in terms of oil recovery with respect to the situation in which these approaches are used separately(the oil recovery is increased by 15.37%).Computer tomography scan results show that with the combined approach,a larger sweep volume and higher oil washing efficiency are obtained.The remaining oil in the cluster form can be recovered in the middle and low permeability layer,increasing the proportion of the columnar and blind end states of the oil.The nuclear magnetic resonance test results show that the combined“plugging,profile control,and flooding”treatment can also be used to control more effectively the dominant channels of the high permeability layer and further expand the recovery degree of the remaining oil in the pores of different sizes in the middle and low permeability layers.However,for the low permeability layer(permeability difference of 20),the benefits in terms of oil recovery are limited.

Controllably Coupling Superconducting Charge and Flux Qubits by Using Nanomechanical Resonator

We propose an effective mechanism to couple superconducting charge and flux qubits by using a quantized nanomechanical resonator. The coupling between the charge and flux qubits can be controlled by the external flux of the charge qubit. Under the strong coupling limR, an iSWAP gate can be generated by this scheme. The experimental feasibility in our scheme is also presented.