Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “impedance control”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 55 records · Page 3Linked to original sources
PubMed1991

Impedance analysis to identify the at risk femorodistal graft.

Computer-assisted impedance analysis is a newly developed technique to identify femoropopliteal and distal vein graft stenoses before failure. Pulsatile flow is measured from the proximal and distal graft by use of an 8Mhz Doppler velocimeter. A pulse volume recorder measures pulsatile pressure within the thigh and calf. Fourier transfer analysis is performed on paired Doppler pulse volume recorder waveforms and an impedance score derived for the thigh and calf, respectively. In a retrospective review of 50 nonreversed femoropopliteal/distal grafts performed for limb salvage, postoperative biplanar intraarterial digital subtraction arteriography was compared with impedance analysis. Arteriography showed graft or runoff stenoses in 22 grafts (at risk) and 28 normal grafts (controls). Impedance scores were significantly higher in the at risk group (0.58 + [0.43 to 0.72]*), when compared with the controls (0.34 + [0.30 to 0.38], p less than 0.001*). A thigh or calf impedance score of greater than 0.45 was able to detect 20 of 22 stenoses, including 6 lesions in grafts with normal resting and postexercise ankle pressures. This score was then applied prospectively and compared with serial biplanar digital subtraction arteriography in a further 56 femoropopliteal/distal bypasses for limb salvage. Thirty-three of 34 lesions were successfully predicted and impedance scores were significantly higher in the at risk limbs (0.56 + [0.44 to 0.68]*) when compared with the controls (0.38 + [0.35 to 0.41], p less than 0.001*). In this series impedance analysis proved more sensitive than resting or stressed ankle pressures and, unlike Duplex scanning, was able to detect runoff as well as graft stenoses.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed2004

Learning to control arm stiffness under static conditions.

We used a robotic device to test the idea that impedance control involves a process of learning or adaptation that is acquired over time and permits the voluntary control of the pattern of stiffness at the hand. The tests were conducted in statics. Subjects were trained over the course of 3 successive days to resist the effects of one of three different kinds of mechanical loads: single axis loads acting in the lateral direction, single axis loads acting in the forward/backward direction, and isotropic loads that perturbed the limb in eight directions about a circle. We found that subjects in contact with single axis loads voluntarily modified their hand stiffness orientation such that changes to the direction of maximum stiffness mirrored the direction of applied load. In the case of isotropic loads, a uniform increase in endpoint stiffness was observed. Using a physiologically realistic model of two-joint arm movement, the experimentally determined pattern of impedance change could be replicated by assuming that coactivation of elbow and double joint muscles was independent of coactivation of muscles at the shoulder. Moreover, using this pattern of coactivation control we were able to replicate an asymmetric pattern of rotation of the stiffness ellipse that was observed empirically. These findings are consistent with the idea that arm stiffness is controlled through the use of at least two independent co-contraction commands.

Adult↗
PubMed1995

Epidermal growth factor attenuates the sclerotherapy-induced biomechanical properties of the oesophagus. An experimental study in minipigs.

BACKGROUND: The effect of epidermal growth factor (EGF) on the biomechanical properties of the oesophagus subjected to sclerotherapy was studied in Goettingen minipigs by means of impedance planimetry. METHODS: Seventeen animals underwent three sessions of weekly endoscopic sclerotherapy. During these 3 weeks and for the subsequent 2 weeks they were treated with either EGF or placebo. After another 3 weeks an impedance planimetric study was done. Ten healthy non-sclerosed pigs were studied as controls. Impedance planimetry was performed by stepwise pressure-induced balloon inflation for analysis of oesophageal cross-sectional area 5 and 10 cm above the gastro-oesophageal junction (GEJ). RESULTS: Systemic treatment with EGF (total daily dose of 30 micrograms/kg/day, administered subcutaneously) for 3 to 7 days per week combined with a weekly paravenous injection of 20-40 micrograms/kg attenuated the oesophageal damage caused by sclerotherapy, implying less pronounced narrowing 5 cm above and less dilation 10 cm above the GEJ. CONCLUSION: These observations suggest a potential therapeutic role for EGF in attenuating sclerotherapy-induced oesophageal injury.

Animals↗
PubMed2002

Manipulating objects with internal degrees of freedom: evidence for model-based control.

There is substantial evidence that humans possess an accurate and adaptable internal model of the dynamics of their arm that is utilized by the nervous system for controlling arm movements. However, it is not known if such model-based strategies are used for controlling dynamical systems outside the body. The need to predict events in the external world is not restricted to the execution of reaching movements or to the handling of rigid tools. Model-based control may also be critical for performing functional tasks with non-rigid objects such as stabilizing a cup of coffee. The present study investigated the strategies used by humans to control simple mass-spring objects. Subjects made straight line reaching movements to a target while interacting with a robotic manipulandum that simulated the dynamics of a one-dimensional mass on a spring. After learning, neither hand nor object kinematics returned to those of free reaching, suggesting that this task was not learned as a perturbation of free reaching. Although there are control strategies (such as slowing the movement of the hand) that would require little or no knowledge of object dynamics, subjects did not adopt these strategies. Instead, they tailored their motor commands to the particular object being manipulated. When object parameters were unexpectedly altered in a way that required no changes in kinematics to successfully complete the task, subjects nonetheless exhibited substantial kinematic deviations. These deviations were consistent with those predicted by a model of the arm-plus-object system driven by a low-impedance controller that incorporated an explicit inverse model of arm-plus-object dynamics. The observed behavior could not be reproduced by a controller that relied on modulating hand impedance alone with no inverse model. These results were therefore consistent with the hypothesis that subjects learn to control the kinematics of manipulated objects by forming an internal model that specified the forces to be exerted by the hand on the object to induce the desired motion of that object.

Adaptation, Physiological↗
PubMed2005

Molecular study of Echinococcus in west-central China.

West-central China is an important endemic focus of both alveolar and cystic echinococcosis where several species of intermediate host are commonly infected with Echinococcus granulosus and E. multilocularis . Isolates of E. granulosus were collected from humans and other animals from different geographical areas of Qinghai, Ningxia, Gansu and Sichuan, and genotyped using the mitochondrial DNA marker ATP synthase subunit 6 gene (atp6). The sheep strain (G1 genotype) of E. granulosus was shown to be the only genotype present in sheep, cattle, goats, yaks and humans in the study areas. However, some heterogeneity in the atp6 sequence was evident in a number of the isolates with the most frequent change being a silent substitution (G/A) at position 360 compared with the G1 reference sequence representing isolates collected from the majority of hosts except humans. Two E. multilocularis isolates examined also had sequences that varied from each other and from the reference E. multilocularis atp6 sequence. The genotypic variation we report may reflect phenotypic differences with important consequences in terms of increased host infectivity for hosts by local Echinococcus strains, possibly impacting on the epidemiology and control of echinococcosis. Such adaptations may also result in different sensitivity to drugs or increased virulence for hosts that will impede control efforts and even affect vaccination strategies against Echinococcus.

Adaptation, Physiological↗
PubMed1996

Variability of impedivity in normal and pathological breast tissue.

The impedivity of six groups of breast tissue is measured between 0.488 kHz and 1 MHz using a hand-held probe, ensuring a constant geometry factor, and a microcomputer-controlled impedance spectroscopy system. 120 spectra are collected in excised tissue samples from 64 patients undergoing breast surgery. Each spectrum consists of 12 frequency points. The mean m, the standard deviation s, and the 'reduced standard error' (epsilon = s/(m N)) of the magnitude and the phase angle of the impedivity are calculated at each frequency for all groups of tissues. The variability at low frequency (f < 10 kHz) is attributed to the dispersion in measurement errors. This contributed to the choice of 32 KHz as the lower limit of measurement frequency in constructed electrical impedance tomograph. The collected data also show that frequencies larger than 1 MHz are needed for the bio-electrical characterisation of breast tissue. In the frequency range used in electrical impedance tomography the reduced standard error of impedivity in breast tissue is about 0.1 or less. The lowest dispersions are observed in the adipose tissue, carcinoma and fibro-adenoma.

Adolescent↗
PubMed2003

Fundamentals of force feedback and application to a surgery simulator.

Force feedback increases the effectiveness of virtual-reality surgery training systems. An overview of the fundamentals of applying force feedback is presented. An impedance control technique and data processing methods for stability preservation are illustrated. A flexible interface for general force-feedback applications has been developed. This interface is capable of controlling several different force-feedback hardware systems, including the SensAble PHANTOM, the Laparoscopic Impulse Engines from Immersion, and the VS-One virtual endoscopic surgery trainer. The findings are evaluated using the main simulation system, KISMET, and the modeling tools KISMO and VESUV. Within the scope of a cooperative project called HapticIO (funded by the German Ministry of Education and Research [BMBF]), new haptic devices have been designed for virtual neuroendoscopy and laparoscopy. The concept and implementations presented in this paper have been found to be flexible, stable and suitable for universal use. The impedance method, combined with the open-loop feed-forward control technique, is well suited and appropriate for the task.

Computer Simulation↗
PubMed2005

Internal models in sensorimotor integration: perspectives from adaptive control theory.

Internal models and adaptive controls are empirical and mathematical paradigms that have evolved separately to describe learning control processes in brain systems and engineering systems, respectively. This paper presents a comprehensive appraisal of the correlation between these paradigms with a view to forging a unified theoretical framework that may benefit both disciplines. It is suggested that the classic equilibrium-point theory of impedance control of arm movement is analogous to continuous gain-scheduling or high-gain adaptive control within or across movement trials, respectively, and that the recently proposed inverse internal model is akin to adaptive sliding control originally for robotic manipulator applications. Modular internal models' architecture for multiple motor tasks is a form of multi-model adaptive control. Stochastic methods, such as generalized predictive control, reinforcement learning, Bayesian learning and Hebbian feedback covariance learning, are reviewed and their possible relevance to motor control is discussed. Possible applicability of a Luenberger observer and an extended Kalman filter to state estimation problems-such as sensorimotor prediction or the resolution of vestibular sensory ambiguity-is also discussed. The important role played by vestibular system identification in postural control suggests an indirect adaptive control scheme whereby system states or parameters are explicitly estimated prior to the implementation of control. This interdisciplinary framework should facilitate the experimental elucidation of the mechanisms of internal models in sensorimotor systems and the reverse engineering of such neural mechanisms into novel brain-inspired adaptive control paradigms in future.

Adaptation, Physiological↗
PubMed2003

Robot-assisted arm trainer for the passive and active practice of bilateral forearm and wrist movements in hemiparetic subjects.

OBJECTIVE: To determine whether use of a robotic arm trainer for bilateral exercise in daily repetitive training for a 3-week period reduced spasticity and improved motor control in the arm of severely affected, chronic hemiparetic subjects. DESIGN: Before-after trial. SETTING: Community rehabilitation center in Germany. PARTICIPANTS: Consecutive sample of 12 chronic hemiparetic patients; minimum stroke interval 6 months; patients could maximally protract the affected shoulder, hold the extended arm, or slightly flex and extend the elbow. INTERVENTIONS: Additional daily therapy of 15 minutes with the arm trainer for 3 weeks; the 1 degree of freedom trainer enabled the bilateral passive and active practice of a forearm pronation and supination and wrist dorsiflexion and volarflexion; impedance control guaranteed a smooth movement. MAIN OUTCOME MEASURES: Patients' impressions, the Modified Ashworth Scale (MAS) score (range, 0-5) to assess spasticity, and the arm section of the Rivermead Motor Assessment (RMA) score (range, 0-15) to assess motor control were rated before therapy, after each 3-week interval, and at follow-up 3 months later. RESULTS: All patients had favorable impressions: the extremity felt more vivid, and 8 subjects noticed a reduction in spasticity, an ease of hand hygiene, and pain relief. The MAS score of the wrist and fingers joints decreased significantly (P<.0125) from a median of 3 (2-3) and 3 (3-4) to 2 (1-2) and 2.5 (2-3). The RMA score minimally increased in 5 cases without improvement in functional tasks. The median RMA score before therapy was 2.0 (1-2) and 2.0 (1-3.75) after therapy. There were no side effects. At follow-up, the effects had waned. CONCLUSIONS: The arm trainer made possible intensive bilateral elbow and wrist training of severely affected stroke patients. Future studies should address the treatment effect in subacute stroke patients and determine the optimum treatment intensity.

Adult↗
PubMed1998

The Jeremiah Metzger Lecture. Vaccine prophylaxis today: its science, application and politics.

In summary, I have addressed 5 key issues concerning vaccines today. First is the essentially empiric nature of vaccinology. Vaccinology is not a rational science. Each idea must be tested by experiment. This need for trial and error experimentation is a substantial barrier to new vaccines. The proven track record of existing vaccines to eradicate disease, to reduce occurrence of disease, reduce human suffering and contain health care spending--when coupled with the potential for new discoveries against significant disease targets--is unparalleled by other therapeutic areas. The complexity of vaccine delivery today in clinical practice with 15-17 injections in the first two years of life emphasizes the need for development of combination pediatric vaccines, for example, putting DTaP, HBV, HIB, and IPV together. This has proved to be far more difficult than previously believed due to unpredicted immune interference and incompatibilities on mixing of different components, demonstrating again the inadequacy of our understanding of how vaccines work and the empiric nature of the science. Similar complexity will face adult vaccines in the future, as new adult vaccines are developed. Next, vaccines remain undervalued by people, by government, and by society. Government-controlled prices in many areas of the world prohibit a return on investment that supports innovative R&D. New vaccines may be unavailable in certain markets because of pricing restraints. Prices of new vaccines in the developed world will rise as will prices in the developing world for products currently available only in the developed world. Reluctance to use vaccines is an especially disturbing symptom of the undervaluation issue. In the U.S., school entry requirements have kept childhood immunization rates high by five years of age. But this is a new phenomenon, driven in part by the measles outbreaks. The risk is that history will repeat itself. In the absence of disease and lack of public knowledge of these diseases, complacency sets in, immunization rates fall, with the expected result on occurrence of disease. For adults, we may hope that managed care with its interest in cost saving and disease prevention may actually help in achieving the goals of the Year 2000. Finally, I have talked about the anti-vaccine attitudes and forces that impede control of disease by vaccines. It is important that new initiatives be undertaken that will be successful in providing a balanced view of vaccine safety, efficacy and benefits to the public, to the provider and to the payers.

Adult↗
PubMed2006

Hysteroscopic surgery.

Hysteroscopy and visually directed endometrial sampling have replaced blind curettage for the diagnosis of endometrial disease. Hysteroscopy can be used to detect endometrial cancer and various premalignant lesions, as well as to diagnose intrauterine polyps and submucous fibroids. It can also be used to locate lost intrauterine devices, assess the shape and size of the endometrial cavity during an infertility work-up and to visualise intrauterine septae and adhesions. If the hysteroscopist possesses special skills and training, it can be used to perform intrauterine sterilisation by occluding the tubal ostia. The ability to perform endometrial ablation as an alternative to hysterectomy in patients with menorrhagia has led to reduction in the number of hysterectomies performed. Long-term follow-up has confirmed the success of this procedure, but it is not without complications. The inherent dangers and complications of endometrial ablation and the considerable skill and training it requires has led to the development of numerous second-generation devices, which can involve balloons that are heated with circulating fluid, impedance-controlled endometrial ablation or surface electrodes, heated fluid running through the hysteroscope under direct vision or the use of microwaves or cryotherapy. This chapter reviews the techniques, potential complications and evidence for the effectiveness of the common diagnostic and therapeutic hysteroscopic procedures.

Electrosurgery↗
PubMed2006

Hepatic radiofrequency ablation using perfusion electrodes in a pig model: effect of the Pringle manoeuvre.

AIM: To assess the influence of the Pringle manoeuvre on volume and geometry of coagulations close to the portal vein using an impedance-controlled radiofrequency ablation system with perfusion electrodes. METHODS: Twelve pigs were randomly assigned to a control group (n = 6) and a group where the Pringle manoeuvre was applied during ablation (n = 6). One coagulation was made in each animal close to the portal vein. All animals were sacrificed 4 days after ablation, and the livers were removed for gross and histopathologic analysis. RESULTS: Effective coagulation volume in the Pringle group (10.8 +/- 5.0 cm(3)) was significantly increased (p = 0.03) compared to the control group (4.1 +/- 4.1 cm(3)). The efficacy ratio, defined as the effective coagulation volume divided by the coagulation volume, was not significantly different in the Pringle group (0.47 +/- 0.27) compared to the control group (0.33 +/- 0.22). The geometrical centre of the effective coagulation volume did not correspond to the position of the ablation electrode. Thermal damage of the gallbladder was found in three animals, all belonging to the Pringle group. CONCLUSIONS: The Pringle manoeuvre was associated with increased effective coagulation volume, but did not significantly influence the predictability of coagulation volume or geometry.

Animals↗
PubMed2003

A micromachined silicon multielectrode for multiunit recording.

A 16-channel multielectrode was used to record propagating action potentials from multiple units in the ventral nerve cord of the cricket Gryllus bimaculatus. The multielectrode was fabricated using photolithographic and bulk silicon etching techniques. The fabrication differs from standard methods in its use of deep reactive ion etching (DRIE) to form the bulk electrode structure. This technique enables the fabrication of relatively thick (>100 microm), rigid structures whose top surface can have any form of thin film electronics. The multielectrode tested in this paper consists of 16 narrow silicon bridges, 150 microm wide and 350 microm tall, spaced evenly over a centimeter, with passive rectangular gold recording sites on the top surface. The nerve cord was placed perpendicularly across the bridges. In this geometry, the nerve spans a 350 microm deep, 450 microm wide trench between each recording site, permitting adequate isolation of recording sites from each other and a platinum ground plane. Spike templates for eight neurons were formed using principle component analysis and clustering of the concatenated multichannel waveforms. Clean templates were generated from a 40 s recording of stimulus evoked activity. Conduction velocities ranged from 2.59+/-0.05 to 4.99+/-0.12 m/s. Two limitations of extracellular electrode arrays are the resolution of overlapping spikes and relation of discriminated units to known anatomy. The high density, precise positioning, and controlled impedance of recording sites achievable in microfabricated devices such as this one will aid in overcoming these limitations. The rigid devices fabricated using this process offer stable positioning of recording sites over relatively large distances (several millimeters) and are suitable for clamping or squeezing of nerve cords.

Action Potentials↗
PubMed2003

Quality of life should be considered the primary outcome for measuring success of endometrial ablation.

STUDY OBJECTIVE: To compare clinical and quality of life outcomes by validated instruments after endometrial ablation by four methods, and determine the primary outcome that most reflects procedure success. DESIGN: Descriptive cohort study (Canadian Task Force classification II-2). SETTING: Minimal-access gynecologic surgery unit in northeast England. PATIENTS: One hundred thirty-nine women. INTERVENTION: Endometrial ablation by one of four methods: Cavaterm, endometrial laser interstitial thermotherapy (ELITT), endometrial laser ablation (ELA), or NovaSure impedance-controlled system. MEASUREMENTS AND MAIN RESULTS: Clinical outcomes were assessed according to menstrual outcome. Whereas amenorrhea rates were significantly different among the four techniques (chi2 = 9.42, p = 0.02), combined amenorrhea and hypomenorrhea rates were not significantly different (67%, 69%, 69%, 62%, chi2 = 0.38, NS) for Cavaterm, ELITT, ELA, and NovaSure, respectively. Quality of life, measured preoperatively by the EQ-5D index and EQ-5D vas, SF-12 physical and mental component scores, and sexual activity questionnaire pleasure, habit, and discomfort scores, were substantially improved 12 months after treatment. No significant differences were seen in quality of life scores between women after endometrial ablation and the general population. CONCLUSION: Quality of life for women with menorrhagia is improved to a normal level by treatment with either first- or second-generation endometrial ablation.

Cohort Studies↗
PubMed2003

Assessment and comparison of intraoperative and postoperative pain associated with NovaSure and ThermaChoice endometrial ablation systems.

STUDY OBJECTIVE: To assess and compare intraoperative and postoperative pain associated with NovaSure impedance-controlled endometrial ablation system and ThermaChoice system. DESIGN: Prospective, international, multicenter, double-arm study (Canadian Task Force classification II-1). Setting. Academic medical centers and private offices. PATIENTS: Sixty-seven premenopausal women with menorrhagia. INTERVENTION: Endometrial ablation with either the NovaSure (37 women) or ThermaChoice (30) system. NovaSure-treated patients received no endometrial pretreatment; those treated with ThermaChoice received the recommended 3-minute suction dilatation and curettage. MEASUREMENTS AND MAIN RESULTS: Standard pain measurement instruments (visual analog scale, numeric rating scale) were used to assess intraoperative and postoperative pain. Serum levels of prostaglandin-F(2alpha) were measured before and 5, 30, and 60 minutes after the procedure. Patients treated with the NovaSure system reported statistically significantly lower intraoperative and postoperative pain than those treated with the ThermaChoice system (p <0.0001). Procedure time was statistically significantly shorter with the NovaSure system (p <0.0001). Prostaglandin-F(2alpha) values did not differ statistically between groups. CONCLUSION: The NovaSure system is associated with statistically significantly lower intraoperative and postoperative pain than ThermaChoice system, and endometrial ablation with NovaSure could become an office-based procedure.

Adult↗
PubMed2002

A randomized, multicenter trial of safety and efficacy of the NovaSure system in the treatment of menorrhagia.

STUDY OBJECTIVE: To compare the safety and effectiveness of the NovaSure impedance-controlled endometrial ablation system with hysteroscopic wire loop resection plus rollerball ablation for treatment of excessive uterine bleeding in premenopausal women. DESIGN: Randomized, multicenter, double-arm study (Canadian Task Force classification I). SETTING: Nine academic medical centers and private offices. PATIENTS: Two hundred sixty-five premenopausal women with symptomatic menorrhagia. INTERVENTION: Ablation performed with the NovaSure system or wire loop resection and rollerball. MEASUREMENTS AND MAIN RESULTS: Success [pictorial blood loss-assessment chart (PBLAC) score < or =75] was achieved in 88.3% of NovaSure-treated and 81.7% of rollerball-treated patients. One year after treatment 90.9% and 87.8%, respectively, reported normal bleeding or less (PBLAC < or =100) and 41% and 35%, respectively, experienced amenorrhea (PBLAC = 0). Mean procedure time was 4.2 minutes (average 84 sec) in the NovaSure group and 24.2 minutes in the rollerball group. Local and/or intravenous sedation was administered in 73% of NovaSure patients and 18% of rollerball patients. Intraoperative adverse events occurred less frequently with NovaSure (0.6%) than with rollerball (6.7%). Postoperative adverse events occurred in 13% and 25.3% of patients, respectively. CONCLUSION: The NovaSure system was safe and effective in treatment of women with menorrhagia. The procedure is both quick and effective, and eliminates the expense and side effects of endometrial pretreatment.

Adult↗
PubMed2005

NovaSure bipolar radiofrequency endometrial ablation: report of 200 cases.

OBJECTIVE: To review the perioperative complications and short-term outcome in women undergoing endometrial ablation for menorrhagia using the NovaSure bipolar radiofrequency impedance-controlled system. METHODS: We conducted a prospective observational study of endometrial ablation using the NovaSure system in 200 women with menorrhagia not amenable to medical management. RESULTS: Of the 200 women treated, 146 have been observed for 1 to 4 years with the following outcomes related to menstrual bleeding: amenorrhea 43.1%, light bleeding 41.8%, normal bleeding 4.1%, and heavy bleeding 11%. Twelve of the 146 women (8.2%) required repeat surgical treatment: hysterectomy in 10 cases and repeat ablation in 2. In the 200 cases, 1 laparoscopy was performed because of uterine perforation at the time of pretreatment hysteroscopy, and 2 patients required antibiotic therapy for postoperative endomyometritis. Of the women observed for 1 to 4 years, 81.5% felt the procedure was successful, and 97.3% would recommend the procedure to a friend. CONCLUSION: Endometrial ablation using the NovaSure system is a simple technique in the normal uterine cavity, which can be performed under local anaesthesia and conscious sedation. The complication rate is low, and the short-term satisfaction and results are good.

Adult↗
PubMed2005

The effect of slow interfacial kinetics on the chronoamperometric response of composite lithiated graphite electrodes and on the calculation of the chemical diffusion coefficient of Li ions in graphite.

This paper deals with a study of the shape of the chronoamperometric response (current, I, vs time, t) and, eventually, the mechanism of Li-ions insertion and deinsertion to/from composite graphite electrodes obtained by a small-amplitude (incremental) technique, such as potentiostatic intermittent titration (PITT). The dependences of log I, the Cottrell parameter It(1/2), and the differential parameter d log I/d log t on the process duration (vs log t) were carefully examined both for single- and two-phase coexistence domains. log I vs log t curves for single-phase domains were characterized by a single monotonic curve with a gradually increasing slope. In contrast, the same curves for two-phase domains consist of two sequential downward concave lines. Both types of response were explained by using the cell-impedance-control model. To separate the contributions of solid-state diffusion, Ohmic drops, and slow interfacial charge-transfer kinetics to the chronoamperometric response, the data were presented in the form of the inverse Cottrell parameter, (It(1/2))(-1) vs t(-1/2), from which the chemical diffusion coefficient (D) could be obtained. Refined values of D for Li insertion into graphite obtained herein agree very well with values of the component diffusion coefficient obtained from quasielastic neutron scattering for Li insertion into HOPG, reported in the literature.

Journal Article↗