Sudden Pressure Changes Research Articles

Intervertebral Neck Injury Criterion for Simulated Frontal Impacts

Objective: The Intervertebral Neck Injury Criterion (IV-NIC) is based on the hypothesis that dynamic intervertebral motion beyond physiological limits may injure soft tissues. In contrast, the Neck Injury Criterion (NIC) hypothesizes that sudden change in spinal fluid pressure may cause neural injuries. The goals of this study, using the biofidelic whole human cervical spine model with muscle force replication, were to determine the IV-NIC injury threshold due to frontal impact at each intervertebral level, and to compare the IV-NIC and NIC in determining injury. Methods: Using a bench-top apparatus, frontal impacts were simulated at 4, 6, 8, and 10 g horizontal accelerations of the T1 vertebra. Pre- and post-trauma flexibility testing measured the soft tissue injury; that is, a significant increase (p < 0.05) in neutral zone or range of motion at any intervertebral level, above the corresponding physiological limit. Results: Results indicated that the soft tissue injury occurred due to flexion mode of injury and its threshold was 8 g. The average IV-NIC injury threshold (95% confidence interval) was 2.0 (1.2–2.8) at C4-C5 and 2.3 (1.6–3.0) at C6-C7, while the average NIC injury threshold was 18.4 (17.9–19.0) m 2 /s 2 . The NIC injury threshold was reached significantly earlier than all the IV-NIC injury thresholds, demonstrating that the NIC may be unable to predict facet and soft tissue injury caused by non-physiologic inververtebral rotation. Conclusions: Present results suggest that IV-NIC is an effective tool for determining soft tissue neck injuries by identifying the intervertebral level, mode, time, and severity of injury.

Oxidation kinetics of ZrNbO in steam: Differences between the pre- and post-transition stages

The oxidation by water vapour of a zirconium based alloy, a ZrNbO alloy containing 1% of Nb, has been studied between 500 and 550 °C, the water vapour partial pressure ranging in 13–80 h Pa, using isothermal and isobaric thermogravimetry, and calorimetry. During gravimetry experiments, sudden changes (jumps) in temperature or water vapour pressure have also been performed. It comes out that the kinetic behaviour is different before and after the transition, even though the approximations of steady-state and rate-limiting step are justified in both stages: the influence of temperature jumps is greater in pre-transition, whereas the effect of water vapour partial pressure is more pronounced in post-transition (nevertheless, an accelerating effect is also observed before the transition). No influence of hydrogen partial pressure has been observed. Besides, the higher the Nb content in the alloy, the higher the oxidation rate (in pre-transition). A mechanism has been proposed to account for the results obtained in pre-transition, involving the diffusion of adsorbed species in the porous part of the oxide layer as rate-determining step. The transition is accompanied by a change in the oxidation mechanism: in the post-transition stage, the kinetic curves being linear, the oxidation may be controlled by an interface step, which is probably different from the steps proposed for the pre-transition mechanism.

Vasoregulatory Responses To Sudden Changes In Forearm Perfusion Pressure During Moderate Forearm Exercise

Exercising muscle blood flow is thought to be tightly regulated to metabolic demand. The time course of vasoregulatory responses to a disruption of steady state exercising muscle blood flow remains unclear. PURPOSE We tested the hypothesis that sudden changes in local forearm perfusion pressure during moderate intensity forearm handgrip exercise would alter forearm blood flow (FBF) and result in rapid compensatory changes in forearm vascular conductance (FVC, vasoregulatory responses) to restore FBF. METHODS 12 healthy young subjects (7 female,5 male) lay supine and were instrumented for brachial artery FBF (Doppler ultrasound), arterial blood pressure (ABP; arterial tonometry) and heart rate (HR;ECG). Exercise consisted of 30% MVC rhythmic isometric handgrip contractions (2 s /2 s contraction/relaxation duty cycle). Rapid changes in arm position between above (AH) and below (BH) heart level (forearm perfusion pressure difference of ∼30 mmHg) during steady state exercise occurred during a 2 s contraction period. Exercise then continued for 4 min in the new arm position. Vasoregulatory responses were examined by analysing cardiac cycles during relaxation between contractions. FVC during exercise was calculated using forearm level ABP. RESULTS AH to BH transition: an immediate increase in FBF (ml/min ±SE) (419.5±56.6 to 708.7±68.5, p < 0.05) and FVC (602.1±94.4 to 709.5±85.4, p < 0.05) was followed by rapid restoration of FVC (ml/min/100 mmHg ±SE) (609.6±88.9, P=1.00) with no further change, and incomplete restoration of FBF (597.0±72.1, p < 0.001). BH to AH transition:an immediate decrease in FBF (551.0±68.6 to 349.1±52.7, p < 0.001) and FVC (540.0±71.3 to 468.3±74.3, P=0.017) was followed by rapid restoration of FVC (511.8±68.5, P=0.970) with no further change, and incomplete restoration of FBF (409.6±54.3, p < 0.001). CONCLUSION Changes in perfusion pressure during exercise result in an immediate change in FBF and perfusion pressure-mediated changes in resistance vessel distension (altered FVC). Rapid acting vasoregulatory mechanism(s) (likely myogenic) respond to restore FVC, with no further vasoregulatory adjustments such that FBF is not restored. Supported by NSERC; Canada Foundation for Innovation; Ontario Innovation Trust

Vasoregulatory Responses To Sudden Changes In Forearm Perfusion Pressure During Moderate Forearm Exercise

Exercising muscle blood flow is thought to be tightly regulated to metabolic demand. The time course of vasoregulatory responses to a disruption of steady state exercising muscle blood flow remains unclear. PURPOSE We tested the hypothesis that sudden changes in local forearm perfusion pressure during moderate intensity forearm handgrip exercise would alter forearm blood flow (FBF) and result in rapid compensatory changes in forearm vascular conductance (FVC, vasoregulatory responses) to restore FBF. METHODS 12 healthy young subjects (7 female,5 male) lay supine and were instrumented for brachial artery FBF (Doppler ultrasound), arterial blood pressure (ABP; arterial tonometry) and heart rate (HR;ECG). Exercise consisted of 30% MVC rhythmic isometric handgrip contractions (2 s /2 s contraction/relaxation duty cycle). Rapid changes in arm position between above (AH) and below (BH) heart level (forearm perfusion pressure difference of ∼30 mmHg) during steady state exercise occurred during a 2 s contraction period. Exercise then continued for 4 min in the new arm position. Vasoregulatory responses were examined by analysing cardiac cycles during relaxation between contractions. FVC during exercise was calculated using forearm level ABP. RESULTS AH to BH transition: an immediate increase in FBF (ml/min ±SE) (419.5±56.6 to 708.7±68.5, p < 0.05) and FVC (602.1±94.4 to 709.5±85.4, p < 0.05) was followed by rapid restoration of FVC (ml/min/100 mmHg ±SE) (609.6±88.9, P=1.00) with no further change, and incomplete restoration of FBF (597.0±72.1, p < 0.001). BH to AH transition:an immediate decrease in FBF (551.0±68.6 to 349.1±52.7, p < 0.001) and FVC (540.0±71.3 to 468.3±74.3, P=0.017) was followed by rapid restoration of FVC (511.8±68.5, P=0.970) with no further change, and incomplete restoration of FBF (409.6±54.3, p < 0.001). CONCLUSION Changes in perfusion pressure during exercise result in an immediate change in FBF and perfusion pressure-mediated changes in resistance vessel distension (altered FVC). Rapid acting vasoregulatory mechanism(s) (likely myogenic) respond to restore FVC, with no further vasoregulatory adjustments such that FBF is not restored. Supported by NSERC; Canada Foundation for Innovation; Ontario Innovation Trust

Analysis of discrete and continuous distributions of ventilatory time constants from dynamic computed tomography

In this study, an algorithm was developed to measure the distribution of pulmonary time constants (TCs) from dynamic computed tomography (CT) data sets during a sudden airway pressure step up. Simulations with synthetic data were performed to test the methodology as well as the influence of experimental noise. Furthermore the algorithm was applied to in vivo data. In five pigs sudden changes in airway pressure were imposed during dynamic CT acquisition in healthy lungs and in a saline lavage ARDS model. The fractional gas content in the imaged slice (FGC) was calculated by density measurements for each CT image. Temporal variations of the FGC were analysed assuming a model with a continuous distribution of exponentially decaying time constants. The simulations proved the feasibility of the method. The influence of experimental noise could be well evaluated. Analysis of the in vivo data showed that in healthy lungs ventilation processes can be more likely characterized by discrete TCs whereas in ARDS lungs continuous distributions of TCs are observed. The temporal behaviour of lung inflation and deflation can be characterized objectively using the described new methodology. This study indicates that continuous distributions of TCs reflect lung ventilation mechanics more accurately compared to discrete TCs.

IMPROVING ANAEROBIC DIGESTER EFFICIENCY BY HOMOGENIZATION OF WASTE ACTIVATED SLUDGE

IMPROVING ANAEROBIC DIGESTER EFFICIENCY BY HOMOGENIZATION OF WASTE ACTIVATED SLUDGEMicroSludge™ is a patented chemical and pressure pre-treatment process that increases both the rate and extent that waste activated sludge (WAS) is degraded in a conventional mesophilic anaerobic digester. The process uses alkaline pre-treatment to weaken cell membranes and an industrial-scale homogenizer to provide an enormous and sudden pressure change to burst the cells. The resulting...Author(s)Barry RabinowitzRob StephensonSourceProceedings of the Water Environment FederationSubjectSession 34: Residuals & Biosolids Management: Anaerobic Digestion PretreatmentDocument typeConference PaperPublisherWater Environment FederationPrint publication date Jan, 2005ISSN1938-6478SICI1938-6478(20050101)2005:13L.2752;1-DOI10.2175/193864705783865578Volume / Issue2005 / 13Content sourceWEFTECFirst / last page(s)2752 - 2771Copyright2005Word count654

Stability analysis of reactive sputtering process with variable sticking coefficients

In reactive sputtering, the introduction of reactive gas would create a hysteresis transition from metal to compound mode in both the target and the substrate. The hysteresis transition is characterized by a sudden change in partial pressure, sputtering rate and fraction of compound formation, etc. Therefore, the stability is an important issue of process control. In this paper, a mathematical model with variable sticking coefficients based on surface kinetics is introduced to study the process stability. The variable sticking coefficient represents different mechanisms for surface reactions from the type of Langmuir to precursors. To facilitate the analysis, several nondimensional parameters are introduced and used for formulation. Results show that, when the chemical reaction on a substrate is moderate, a higher sputtering yield of the compound leads to a more stable steady-state at lower inflow rates. However, when the ratio of sputtering yield (compound/metal) is zero, there is no hysteresis transition because of the deposition of pure metal (single phase) on the substrate. For different sticking mechanisms, the precursor type is found to make the surface easier to saturate with compound due to its higher default sticking coefficient and the lower pressure and inflow rate for the hysteresis transition.

Comparison of regional vasomotor responses to acetazolamide and CO2 in rabbit cerebrum and cerebellum, measured by a hydrogen clearance method

Many investigators have proved the usefulness of acetazolamide provocation and the carbon dioxide test for assessment of the local cerebrovascular reactivity by measurement of the regional cerebral blood flow in patients with occlusive cerebrovascular disease. Data originating from a comparison of these two different vasomotor stimuli as concerns the differences in sensitivity to them in various parts of the central nervous system are scarce. Our aim was to compare the cerebral blood flow responses to hypercapnic and acetazolamide stimuli in different brain regions. The cerebral blood flow was measured in the cerebrum (cortex and caudate nucleus) and cerebellum (cortex), as measured by a hydrogen clearance method in anaesthetized, artificially ventilated rabbits. In normocapnia, the cerebral blood flow values in the cerebrum and the cerebellum differed significantly. The cerebral blood flow responses to both vasodilatory stimuli were to be significantly higher in the cerebrum than in the cerebellum, but the relative increases, i.e. the mean relative reactivities, were similar in the different regions measured. The regional dissimilarity might explain to some extent the different sensitivities of the various brain areas to sudden blood pressure changes (infarction or haemorrhage). The results further suggest that heterogeneity in cerebrovascular reactivity should be considered in the assessment of vasoreactivity in patients with occlusive cerebrovascular disease. Since the comparison of the carbon dioxide and acetazolamide-induced cerebrovascular reactivities revealed a strong linear relationship, it was concluded that acetazolamide provocation is equivalent to the carbon dioxide test in the evaluation of cerebrovascular reactivity.

Macular hemorrhage after laser in situ keratomileusis (LASIK) with femtosecond laser flap creation

To report the first case of macular hemorrhage following laser in situ keratomileusis (LASIK) with femtosecond laser flap creation. Observational case report. A 36-year-old woman underwent uncomplicated, bilateral, simultaneous LASIK procedures for correction of moderate myopia (-5.00 diopters OD and -6.00 diopters OS). LASIK flap creation was performed using the IntraLase femtosecond laser. On postoperative day 1, the patient's uncorrected and best-corrected visual acuities were 20/20 OD and 20/40 OS. A dilated fundoscopic examination revealed a one-third disk diameter macular hemorrhage OS. An intravenous fluorescein angoiogram ruled out the presence of predisposing macular pathology. Two months after LASIK, the macular hemorrhage had cleared, and 6 months later, the BCVA improved to 20/25 OS. Macular hemorrhage may occur after LASIK, even in the absence of previously identified risk factors, such as high myopia, pre-existing choroidal neovasculaization, lacquer cracks, and sudden changes in intraocular pressure associated with microkeratome-assisted flap creation.

Evaluation of the intervertebral neck injury criterion using simulated rear impacts

The Intervertebral Neck Injury Criterion (IV-NIC) is based on the hypothesis that intervertebral motion beyond the physiological limit may injure spinal soft tissues during whiplash, while the Neck Injury Criterion (NIC) hypothesizes that sudden changes in spinal fluid pressure may cause neural injury. Goals of the present study, using a biofidelic whole cervical spine model with muscle force replication, were to correlate IV-NIC with soft-tissue injury, determine the IV-NIC injury threshold, and compare IV-NIC and NIC. Using a bench-top apparatus, rear-impacts were simulated at 3.5, 5, 6.5, and 8 g horizontal accelerations of the T1 vertebra. Pre- and post-whiplash flexibility tests measured the soft tissue injury threshold, i.e. significant increases in the intervertebral neutral zone (NZ) or range of motion (ROM) above corresponding baseline values. Extension IV-NIC peaks correlated well with NZ and ROM increases at C0–C1 and at C3–C4 through C7–T1 ( r=0.64 and 0.62 respectively, p<0.001). Average IV-NIC injury thresholds (95% confidence limits) varied among the intervertebral levels and ranged between 1.5 (1.1, 1.9) at C5–C6 and 3.4 (2.4, 4.4) at C7–T1. The NIC injury threshold was 8.7 (7.7, 9.7) m 2/s 2, substantially less than the proposed threshold of 15 m 2/s 2. Results support the use of IV-NIC for determining the cervical spine injury threshold and injury severity. Advantages of IV-NIC include the ability to predict the intervertebral level, mode, severity, and time of the cervical spine soft-tissue injury.

유체-고체 상호작용 (FSI)기법을 이용한 이엽기계식 인공심장판막을 지나는 혈액유동과 판첨거동에 관한 수치해석적 연구

Bileaflet mechanical valves have the complications such as hemolysis and thromboembolism, leaflet damage, and leaflet break. These complications are related with the fluid velocity and shear stress characteristics of mechanical heart valves. The first aim of the current study is to introduce fluid-structure interaction method for calculation of unsteady and three-dimensional blood flow through bileaflet valve and leaflet behavior interacted with its flow, and to overcome the shortness of the previous studies, where the leaflet motion has been ignored or simplified, by using FSI method. A finite volume computational fluid dynamics code and a finite element structure dynamics code have been used concurrently to solve the flow and structure equations, respectively, to investigate the interaction between the blood flow and leaflet. As a result, it is observed that the leaflet is closing very slowly at the first stage of processing but it goes too fast at the last stage. And the results noted that the low pressure is formed behind leaflet to make the cavitation because of closing velocity three times faster than opening velocity. Also it is observed some fluttering phenomenon when the leaflet is completely opened. And the rebounce phenomenon due to the sudden pressure change of before and after the leaflet just before closing completely. The some of time-delay is presented between the inversion point of ventricle and aorta pressure and closing point of leaflet. The shear stress is bigger and the time of exposure is longer when the flow rate is maximum. So it is concluded that the distribution of shear stress at complete opening stage has big effect on the blood damage, and that the low-pressure region appeared behind leaflet at complete closing stage has also effect on the blood damage.

Effects of variable sticking coefficients on the stability of reactive sputtering process

In reactive sputtering, the introduction of a reactive gas can lead to a hysteresis transition from metal to compounds in both the target and substrate. The hysteresis transition is characterized by a sudden change in partial pressure, sputtering rate, fraction of compound formation, etc. Therefore, stability is an important issue in the process control. In this paper, a mathematical model with variable sticking coefficients based on surface kinetics is used to study the stability of the process. The variable sticking coefficient represents different mechanisms for surface reactions from the Langmuir to precursor type. In order to facilitate the analysis, several nondimensional parameters are identified and used for formulation. Results show that an unsteady system converges to a steady state relatively fast at low inflow rates. With an eigenvalue analysis, the range of positive eigenvalues is consistent with the presence of a hysteresis loop. It is also found that when the chemical reaction on the substrate is moderate, a higher sputter yield of the compound leads to a more stable steady state at lower inflow rates. Regarding the sticking mechanism, for the type of precursors with the parameter k < 1, the compound is easier to form and saturate on the surface due to the higher default sticking coefficient and the lower operating conditions for the hysteresis transition.

Effects of adsorption of alcohol and water on the electrical transport of carbon nanotubebundles

In situ studies on the effects of physisorption of various alcohol molecules(CnH2n+1OH;n = 1–4) on the transport properties of thin films of bundled single-walled carbonnanotubes reveal large increases in the thermoelectric power (TEP)S () and four-probe resistance R () at 40 °C. Interestingly, exposure to water causes virtually no change in the TEP, although theelectrical resistance shows a change of , typical for the alcohols. We observe a simple exponential response ofS(t) and R(t) to a sudden change in the molecular pressure. The characteristic time constants ( min) for S and R are found to be essentially the same for a given molecule, indicating thatthe changes in these transport properties track each other. In fact, plots ofS versus ΔR are linear, the slopes depending on the specific molecule. The transportresults are interpreted in terms of a Boltzmann model and the introductionof a new scattering channel for charge carriers in metallic tubes due toweak interactions with physisorbed molecules. The trends in the changes inS and R with adsorption of these polar molecules can be explained on the basis of the interplaybetween the adsorption energy and the molecular coverage on the nanotube surfaces.

106 エレベーターかご内気圧制御システムの開発

An air pressure control system has been developed to vary air pressure inside the cars of the elevators installed in the Taipei Financial Center, Taipei, Taiwan, traveling at 1010m per minute. (Down rated speed 600m/minute) When traveling up and down in a high-speed elevator in a skyscraper, passengers may feel uncomfortable because of blocked ears caused by the sudden change in air pressure due to high-speed traveling in a skyscraper. Passengers sometimes fell pain in their ears. A report was submitted stating that as a technique to mitigate this discomfort, control of air pressure inside elevator cars to a steady rate of change from start to end of elevator traveling would be effective in enhancing the comfort of passengers. This paper reports the system (control equipment) configuration of the air pressure control system developed to control air pressure inside elevator cars to a steady rate of change, car enclosure structure, car entrance/exit structure, air pressure controller and results of the control performance in a test tower.

Magnetospheric response to sudden changes in solar wind dynamic pressure inferred from polar cap index

We have used the polar cap (PC) index, which is a measure of magnetic disturbance caused by the transpolar portion of ionospheric currents associated with global convection, to investigate the effect of sudden changes in the solar wind dynamic pressure (PSW). We find that during a period of steady interplanetary magnetic field (IMF), the PC index shows an enhancement that is a direct response to an enhancement in PSW. Examination of the response associated with the passage of interplanetary clouds accompanied by magnetic storms shows that a PSW pulse can cause changes in the PC index that are as large as the effects due to the changes in the interplanetary electric field. Responses of the PC index, AE index, and low‐latitude horizontal component of magnetic field are observed to be similar, though during a magnetic storm, the influence of a significant ring current can distort the dayside low‐latitude response. Sudden increases in PSW lead to an initial negative spike in the PC index that is followed by the main increase. Sudden decreases in PSW are found to have the opposite effect: an initial positive spike that is followed by a decrease in the PC index. The spike of ∼3 min duration is found to initiate simultaneously with the sudden impulse or commencement and an AE spike on the ground and the same time that geosynchronous particle fluxes start to increase sharply in response to magnetic field compression. It likely reflects a temporal response of convection to an abrupt change in PSW that is initially of the opposite sign to the more prolonged response, and it may be associated with short time scale current vortices that have been observed in the ionosphere near noon. The above results show that both PSW and IMF play a significant role in controlling the strength of magnetospheric convection.

From pump to molecules.

In response to Eduardo Marban’s invitation to prepare a brief reminiscence on the occasion of the 50th anniversary of Circulation Research , I recount here a few of the ideas and events that have marked my 47 years in research. My research career began when, fresh from a surgical internship at the Johns Hopkins Hospital, I arrived at the then National Heart Institute in 1956. There, having watched Andrew Morrow perform transbronchial left heart catheterization, I thought there must be a better way. I soon became immersed in developing a method for transseptal left heart catheterization, first in dogs, then in human cadavers, and finally in patients; thus, my first research experience proved to be “translational.” It was satisfying to later see this approach used for balloon mitral valvuloplasty and in cardiac electrophysiology. In the early 1960s, there was considerable ferment in the Cardiology Branch of the National Heart Institute in Bethesda within a group of investigators brought together by Eugene Braunwald, one important aspect of which concerned cardiac function. We discussed the current state of cardiac physiology, comparing the approach of Robert Rushmer in intact animals with that of Stanley Sarnoff in the tightly regulated isolated supported heart. Playfully, we formulated two laws of the heart: Rushmer’s Law “When nothing is held constant everything changes” and Sarnoff’s Law “When everything is held constant nothing changes.” Stimulated primarily by the work of Ed Sonnenblick (then at the NIH), I pondered how we might begin to apply the principles of isolated muscle mechanics to the intact heart using an approach in which only one component of an otherwise intact system is perturbed. Assisted by Jim Covell, a method was devised for assessing cardiac function that involved sudden changes in aortic pressure during a single diastolic interval so that the subsequent heartbeat …

Differences in reactivity of oxide growth during the oxidation of Zircaloy-4 in water vapour before and after the kinetic transition

The oxidation of Zircaloy-4 by water vapour has been studied between 500 and 550 °C, the water vapour partial pressure ranging in 13–80 hPa, using isothermal and isobaric thermogravimetry, and calorimetry. During gravimetry experiments, sudden changes in temperature or water vapour pressure have also been performed. It results that the approximations of steady state and rate-limiting step are only valid before the kinetic transition. In the post-transition region, a significant influence of water vapour and hydrogen partial pressures has been found, contrarily to the kinetic behaviour before the transition (which is in this last case, in good agreement with a rate-limiting step of diffusion of oxygen vacancies). It comes out that the post-transition kinetic behaviour is definitely not the same as before the transition.

Perioperative Hearing Impairment

Perioperative Hearing Impairment

Bursts of ULF noise excited by sudden changes of solar wind dynamic pressure

Abstract. We present the results of analysis of the dayside magnetic pulsation response to a sudden change in solar wind dynamic pressure. We concentrate on the events when a burst or a series of short-lived bursts in the Pc1 frequency range with the repetition period of 7–15 min were observed on the ground around the local noon. Not every impulse of large amplitude caused this phenomenon. We have found that the ULF bursts were excited when the spectrograms of the DMSP satellites showed a signature of 10–30 keV ions in the vicinity of the magnetic flux tube of the ground observatory, that may be related to a geomagnetic storm preceding the event. In light of this finding a possible model of the phenomenon is suggested in which the hot protons influence significantly both the generation and modulation of Pc1 activity.Key words. Magnetospheric physics (solar wind – magnetosphere interaction; MHD waves and instabilities; storms and substorms)

Modulation of Jupiter's main auroral oval emissions by solar wind induced expansions and compressions of the magnetosphere

It has recently been suggested that the jovian ‘main auroral oval’ is associated with the region of upward-directed field-aligned currents in the circuit formed through angular momentum exchange between the atmosphere–ionosphere and the equatorial iogenic magnetospheric plasma. It has also been suggested that the luminosity of these emissions should be modulated primarily by the dynamic pressure of the solar wind, which causes expansions and compressions of the magnetosphere and thereby changes the angular velocity of the magnetospheric plasma and the strength of the coupling currents. Here we present a quantitative demonstration of these effects. We consider an initial empirically based middle magnetosphere field and plasma configuration extending to 50 R J, which expands outwards to 70 R J, or is compressed inwards to 30 R J, due e.g. to sudden changes in the dynamic pressure of the solar wind. Changes in the angular velocity of the plasma are computed from the flux-preserving motions of the field lines using conservation of angular momentum. The initial configuration produces a band of aurora in which the luminosity falls over ∼1° latitude from ∼200 kR at the poleward boundary to ∼20 kR . Expansion of the current sheet to 70 R J produces a significant increase in luminosity over this range, with the largest effect occurring at the poleward boundary where a thin (∼50– 100 km ) arc-like structure of MR intensity is formed. The initial emission is reduced by about an order of magnitude for a compression to 40 R J, and essentially to zero for a compression to 35 R J, when the middle magnetosphere plasma is brought to near rigid corotation over the whole radial range such that the coupling current system is essentially switched off. Further compression to 30 R J then induces significant super-corotation, with a reversal in sense of the magnetosphere–ionosphere coupling current system. In this case the middle magnetosphere field-aligned currents reverse to downward throughout, such that we would not expect them to be associated with bright electron-induced auroras. However, upward-directed ‘return’ currents then flow in the poleward region outside of the middle magnetosphere, which may be associated with an auroral oval lying poleward of the usual ‘main oval’ location. A ‘Hill-type’ equilibrium will re-form on time scales of a few tens of hours, and with it, the main oval auroras will re-emerge, corresponding to the changed size of the magnetospheric cavity.