Can sodium MRI be used as a method for mapping of cartilage stiffness?

Objective

Sodium concentration is responsible for (at least part of) the stiffness of articular cartilage due to the osmotic pressure it generates. Therefore, we hypothesized that we could use sodium MRI to approximate the stiffness of cartilage to assess early cartilage degeneration.

Methods

Four human tibial plateaus were retrieved from patients undergoing total knee replacement (TKR), and their cartilage stiffness mapped with indentation testing, after which samples were scanned in a 7 T MRI to determine sodium concentration. The relation of biomechanical parameters to MRI sodium and glycosaminoglycan (GAG) concentration was explored by a linear mixed model.

Results

Weak correlations of GAG concentration with apparent peak modulus (p?=?0.0057) and apparent equilibrium modulus (p?=?0.0181) were observed and lack of correlation of GAG concentration versus MRI sodium concentration was observed. MRI sodium concentration was not correlated with apparent peak modulus, though a moderate correlation of MRI sodium concentration with permeability was shown (p?=?0.0014).

Discussion and conclusion

Although there was correlation between GAG concentration and cartilage stiffness, this was not similar with sodium concentration as measured by MRI. Thus, if the correlation between MRI sodium imaging and GAG concentration could be resolved, this strategy for assessing cartilage functional quality still holds promise.

     

POSITION CONTROL OF A TWO DEGREE-OF-FREEDOM ACTUATOR

Abstract

The paper describes control of a helical-motion induction motor (HMIM) which can be used in a tandem arrangement of two units to form a direct-acting, two degree-of-freedom actuator capable of producing pure rotary motion, pure linear motion, or helical motion. A microprocessor-based controller is designed to drive this closed-loop position control actuator. A proportional control with high gain about command position is implemented to give a desired stiffness coefficient. Using the microprocessor system, an artificial viscous damping is introduced to enhance the dynamic performance.     

OPTIMIZATION OF AN EDDY CURRENT DAMPER

Abstract

An eddy current damping device containing a metal disk moving in a magnetic field of cylindrical symmetry is studied. Analytic equations are presented for the damping which is produced by permanent magnets for a wide range of geometrical parameters of the device. The geometry leading to the maximal damping under size constraints is obtained.     

On the Rotor Angle and Voltage Dynamics Decoupling in Synchronous Generators with Nonlinear AVR

Abstract

In this paper, rotor angle and voltage dynamics decoupling in a synchronous generator connected to an infinite bus using a partial feedback linearization-based nonlinear voltage regulator (FBLAVR) is described. It is well known that the fast voltage regulation using static excitation system introduces negative damping in the system. If this coupling can be eliminated then one can simultaneously achieve fast voltage regulation and desired damping performance. This paper identifies such a decoupling behavior using an FBLAVR and shows that the damping with the FBLAVR only depends on the inherent damping of the machine. The necessity of a power system stabilizer (PSS) is identified even with the FBLAVR, if the natural damping is not sufficient. Thus motivated, an FBLAVR?+?PSS control scheme is proposed and compared with a linear automatic voltage regulator (AVR)?+?PSS control scheme. It is shown that the generator-exciter-power system [GEP(s)] characteristics with FBLAVR does not change with the system operating conditions. The superiority of the proposed control scheme is validated over a wide range of operating conditions on a single machine infinite bus (SMIB) power system.     

ACTIVE DAMPING OF MAGLEV VEHICLES USING SUPERCONDUCTING LINEAR SYNCHRONOUS MOTORS

ABSTRACT

This paper explores the use of linear synchronous motor control to provide active damping for magnetically-levitated vehicles. Using a single LSM, only heave and surge damping can be provided, but, with a dual LSM, roll and yaw damping can also be achieved. The paper gives design data applicable to the reference design of theCanadian 500 km/h Maglev system.     

Comparison Between Single Shield with Damping Winding and Two-Shield Damping System for Superconducting Generators

ABSTRACT

This paper makes a comparison of damping performance between two types of damping/shielding systems for superconducting generators. The first of these, used in the HIT/DOE machine employs a discrete winding plus a shield. The second is the more traditional double shield system. The method of analysis used in the paper employs the Laplace Transform of the operational impedances.     

TURBINE-GENERATOR SHAFT TORQUES AND FATIGUE LIFE EXPENDITURE PREDICTED BY FREQUENCY DOMAIN AND TIME DOMAIN METHODS FOLLOWING SEVERE DISTURBANCES ON THE SYSTEM SUPPLY

ABSTRACT

This paper examines precision of predicting time responses for torque in turbine-generator-exciter shafts together with fatigue life expenditure of shafts by frequency domain analysis not analysed in the literature heretofore following incidence and clearance of worst-case disturbances on the electrical supply system. Effect of both governor and avr action following a range of disturbances is also illustrated. The effect of steam and electrical viscous damping on maximum and minimum shaft torques predicted by frequency domain analysis for a range of disturbances as a function of the fault clearing time is also depicted

The analysis is based on Fourier analysis of generator airgap torque following incidence and clearance of a severe supply network disturbance or following mal-synchronisation to obtain torque excitation which acts on the generator rotor corresponding to each modal vibration. Amplitude and phase of each modal vibration is thereby determined. Using appropriate damping, time responses for shaft torque at each shaft cell is constructed by summing components which correspond to each modal vibration. These time responses are compared with those obtained by solution of more than 50 differential equations which simulate the shaft train, turbine, generator, governor and avr

It is shown that time responses for transient turbine-generator-exciter shaft torques together with maximum shaft torques and fatigue life expenditure of the shaft can be predicted faithfully by frequency domain analysis taking due account of magnitude and phase of each modal vibration, and damping, following (i) worst-case Line-Line-Line, Line-Line, and Line-Ground disturbances from full-load to no-load with clearance, and (ii) mal-synchronisation. Simulation of damping of rotor swing, together with governor action, is important in making precise assessments of transient turbine shaft torque (and fatigue life expenditure of the shaft) at shaft locations which are close to die generator

660 MW, 1000 MW and 1300 MW two-pole Machines are analysed.     

SYNCHRONIZING TORQUE MATRICES AND STATIC BIFURCATIONS IN MULTIMACHINE POWER SYSTEMS

Abstract

The synchronizing torque matrices are used to characterize the transition from stability to instability in a multimachine power system. This transition is called a bifurcation. In this paper we concentrate on static bifurcations. Two representaions are used: the clssical and a detailed one. It is shown that steady state instabilty can be identified by checking the signs of the eigenvlues of the synchronizing matrix. This method has the advantage of applicability to any representation classical or detailed. It also provides a more convenient alternative to the identification of instability by the sign of the determinant of the Jacobian as suggested in the Russian literature. The method is checked using two systems: one with five machines and the other with ten.     

SUBSYNCHRONOUS RESONANCE (SSR) COUNTERMEASURES APPLIED TO THE SECOND BENCHMARK MODEL

ABSTRACT

The aim of the present paper is 10 investigate two types of SSR countermeasures :

a) Phase shifters used to modulate the generator real power

b) Static VAR compensator (SVC) and its auxiliary controllers.

An eigenvalue analysis method is used to study the effectiveness of these countermeasures in damping SSR on the second system of the second IEEE SSR Benchmark model. The method is based on the linearization of the coupled electrical and mechanical equations under small perturbations. An analytical expression of the electrical subsynchronous frequency is expressed as a function of different parameters of the power system. Results concerning the variations of the decrement factors (real part of the eigenvalues) of the torsional modes are presented for different cases.     

Brillouin and raman spectra anomalies in knsbn with the tungsten bronze structure

Abstract

The Brillouin and Raman scattering from a complex single crystal from the tungsten-bronze family, (K_0.5Na_0.5)_0.2(Sr_0.75Ba_0.25)_0.9Nb₂O₆ doped with Cu²⁺ (KNSBN:Cu), have been comparatively studied in a wide temperature range around the ferroelectric transition. Step-like anomalies in hypersonic velocity and damping confirm the first-order structural transition. These anomalies look like some perturbations on the high-temperature slopes of both a broad dip in sound velocity and a broad maximum in damping that develop in a wide temperature range. The acoustic behavior of KNSBN:Cu does not simply follow the Landau theory prediction valid for many ferroelectrics except relaxors, to which the KNSBN:Cu behavior is intrinsically analogous. The total intensity of the Raman spectra as well as the intensity of separate internal and external vibrations and their width correlate with acoustic anomalies, namely there are step-like drops at the same temperature of the first-order transition and a broad range where the intensity is drastically increased.     

VOLTAGE COLLAPSE AND CONTROL ACTIONS: EFFECTS AND LIMITATIONS

ABSTRACT

This paper focuses on control actions determination for voltage collapse prevention. Sensitivity matrices are proposed based on the knowledge of the critical bus. By critical bus one means that bus whose state variables vary at most at the voltage collapse point. A tangent vector is used to identify the critical bus, and its behavior as a function of load increase is also investigated and compared with other indices previously proposed. It is shown that generator control actions may not work to increase voltage collapse margin, whereas local control actions may produce better results. The tests are carried out in the IEEE-300 bus test system, with and without reactive power limits consideration.     

Dynamic Response of Voltage-Driven Induction Machines

Abstract

When operated at rated frequency, typical induction machines exhibit simple first or second order dynamic response depending upon machine size and load inertia and damping. At reduced frequency much more complex behavior can occur including the possiblity of small signal instability. This paper presents a general analysis of small signal dynamic behavior and introduces non-dimensional quantities which allow easy estimation of the region of poor dynamic response for specific machines. Graphical results which illustrate the regions of instability and poor damping are presented. The influence of machine parameters is described and the trends to be expected for different size and types of machines are discussed. In particular, 1t 1s shown that all machines pass through a minimum damping region as the frequency 1s reduced and that larger, more efficient machines will often exhibit small signal instability. An important result of the analysis is that all of the modifications made 1n producing “high efficiency machines” tend to produce more poorly damped behavior in the minimum damping region.     

ON-LINE ESTIMATION OF SYNCHRONIZING AND DAMPING TORQUE COEFFICIENTS USING AN ARTIFICIAL NEURAL NETWORK BASED APPROACH

ABSTRACT

This paper presents an artificial neural network based on-line approach to assess the dynamic stability of a single machine connected to an infinite bus system. The proposed approach is based on estimating the synchronizing and damping torque coefficients of the synchronous machine from voltage and power on-line measurements. Test results show that the proposed approach is very encouraging for fast evaluation of the dynamic stability.     

PARAMETER IDENTIFICATION OF A SEPARATELY EXCITED OC MOTOR FOR SPEED CONTROL

ABSTRACT

This paper presents the application of the least error squares (LES) parameter identification algorithm to. obtain parameters of a separately excited DC motor. The parameters of interest are; the resistance and inductance of the armature windings (Ra.Lt). the motor inertia (J), the damping constant (D), the torque and back emf constant (K) and the load torque constant (μ.). The data used are the motor input voltage, and the corresponding rotor speed. It is assumed that the trajectory of the motor speed as well as the corresponding input voltage are known and sampled at a preselected rate. Simulation results for a separately excited dc motor used in robotics are reported showing good agreement with actual parameter values.     

Dynamic Stabilization of Power Systems through Reactive Power Modulation

ABSTRACT

This paper demonstrates the significant benefits in the dynamic stability improvement of power systems by reactive power modulation in response to a local control signal derived from bus frequency. Static var compensator (SVC) with a thyristor controlled reactor scheme is considered for reactive power modulation.

The benefits of reactive power modulation are dependent on the location of SVC in a multimachine system. A simple criterion based on eigenvalue aensitivity is proposed for the prediction of the effectiveness of the damping control. An illustrative example is given to demonstrate its utility.     

DAMPING OF TORSIONAL OSCILLATIONS–A COORDINATED APPROACH

ABSTRACT

Damping of torsional oscillations using coordinated control through power system stabilizer (PSS) and thyristor controlled reactor(TCR) is presented in this paper. The PSS has modal speed deviations as its feedback signal. The reactive power control is achieved through thyristor controlled reactor (TCR) at the machine terminals. Generator speed deviation is used as auxiliary signal and terminal voltage feedback signal as main control signal for TCR. The following control strategies have been analysed :

a PSS with modal speed control

b PSS with modal speeds plus TCR with terminal voltage control

c PSS with modal speeds plus TCR with complete controls (voltage feed back signal and generator speed deviation signal)

The main objective of this paper is to discuss the modelling aspects and analyse different control strategies for damping torsional oscillations in series compensated ac transmission system. The control parameters like gains and time constants have been obtained by performing repeated eigenvalue analysis. IEEE First Benchmark Model is considered for illustration.     

CDP-choline accumulation in breast and colorectal cancer cells treated with a GSK-3-targeting inhibitor

Purpose

Glycogen synthase kinase 3 (GSK3) is a key controlling element of many cellular processes including cell-cycle progression and recent studies suggest that GSK3 is a potential anticancer target. Changes in glucose metabolism associated with GSK3 inhibition may impact on lipid synthesis, whilst lipid metabolites can act as molecular response markers.

Methods

Here, SKBr3 breast and HCT8 colorectal cancer cells were treated with the GSK3 inhibitor SB216763, and [¹⁴C (U)] glucose and [³H] choline incorporation into lipids was determined. Cell extracts from treated cells were subject to ³¹P NMR spectroscopy.

Results

SB216763 treatment decreased choline incorporation into lipids and caused an accumulation of CDP-choline which was accompanied by decreased conversion of glucose into lipid components.

Conclusion

SB216763 profoundly inhibits phospholipid synthesis in cancer cells which demonstrate accumulation of CDP-choline detectable by ³¹P NMR spectroscopy. Metabolic changes in lipid metabolism present potential response markers to drugs targeting GSK3.

     

Ramping down a clinical 3 T scanner: a journey into MRI and MRS at 0.75 T

Object

Lower-field MR is reemerging as a viable, potentially cost-effective alternative to high-field MR, thanks to advances in hardware, sequence design, and reconstruction over the past decades. Evaluation of lower field strengths, however, is limited by the availability of lower-field systems on the market and their considerable procurement costs. In this work, we demonstrate a low-cost, temporary alternative to purchasing a dedicated lower-field MR system.

Materials and Methods

By ramping down an existing clinical 3 T MRI system to 0.75 T, proton signals can be acquired using repurposed ¹³C transmit/receive hardware and the multi-nuclei spectrometer interface. We describe the ramp-down procedure and necessary software and hardware changes to the system.

Results

Apart from presenting system characterization results, we show in vivo examples of cardiac cine imaging, abdominal two- and three-point Dixon-type water/fat separation, water/fat-separated MR Fingerprinting, and point-resolved spectroscopy. In addition, the ramp-down approach allows unique comparisons of, e.g., gradient fidelity of the same MR system operated at different field strengths using the same receive chain, gradient coils, and amplifiers.

Discussion

Ramping down an existing MR system may be seen as a viable alternative for lower-field MR research in groups that already own multi-nuclei hardware and can also serve as a testing platform for custom-made multi-nuclei transmit/receive coils.

     

AN ELASTIC NONLINEAR POWER SYSTEM STABILIZER

ABSTRACT

The paper presents a novel, simple, variable structure, self adjusting, squashable error-driven, adjustable gain power system stabilizer (PSS) design. The elastic error-driven and error-scaled PSS design falls in between the categories of bang-bang and linear error scaled variable gain. The digital simulation studies were conducted on a single machine infinite bus system. From the digital simulation results, the proposed PSS is shown to be very effective in damping the oscillations and it is robust as it tolerates any system structural and parametric variations. In addition, the proposed PSS can be easily implemented.

The design was simulated and tested using MATLAB simulation package software and compared to conventional analog gain/lead/lag compensator PSS design.     

Clinical evaluation of ultra-high-field MRI for three-dimensional visualisation of tumour size in uveal melanoma patients,with direct relevance to treatment planning

Objectives

To assess the tumour dimensions in uveal melanoma patients using 7-T ocular MRI and compare these values with conventional ultrasound imaging to provide improved information for treatment options.

Materials and methods

Ten uveal melanoma patients were examined on a 7-T MRI system using a custom-built eye coil and dedicated 3D scan sequences to minimise eye-motion-induced image artefacts. The maximum tumour prominence was estimated from the three-dimensional images and compared with the standard clinical evaluation from 2D ultrasound images.

Results

The MRI protocols resulted in high-resolution motion-free images of the eye in which the tumour and surrounding tissues could clearly be discriminated. For eight of the ten patients the MR images showed a slightly different value of tumour prominence (average 1.0 mm difference) compared to the ultrasound measurements, which can be attributed to the oblique cuts through the tumour made by the ultrasound. For two of these patients the more accurate results from the MR images changed the treatment plan, with the smaller tumour dimensions making them eligible for eye-preserving therapy.

Conclusion

High-field ocular MRI can yield a more accurate measurement of the tumour dimensions than conventional ultrasound, which can result in significant changes in the prescribed treatment.