Chua's circuit 10 years later

More than 200 papers, two special issues (Journal of Circuits, Systems, and Computers, Vol.3, Nos. 1 and 2, 1993; IEEE Transactions on Circuits and Systems, Vol. 40 No 10, 1993), an international workshop on ‘Chua's Circuit: Chaotic Phenomena and Applications’ at NOLTA ‘93, and a book (R. N. Madan (ed.), Chua's Circuit: A Paradigm for Chaos, World Scientific, Singapore, 1993) on Chua's circuit have been published since its inception a decade ago. This review paper attempts to present an overview of these timely publications, almost all within the last six months, and to identify four milestones of this very active research area. An important milestone is the recent fabrication of a monolithic Chua circuit. the robustness of this IC chip demonstrates that an array of Chua circuits can also be fabricated into a monolithic chip, thereby opening the floodgate to many unconventional applications in information technology, synergetics and even music. The second milestone is the recent global unfolding of Chua's circuit obtained by adding a linear resistor in series with the inductor to obtain a canonical Chua circuit—now generally referred to as Chua's oscillator. This circuit is most significant because it is structurally the simplest (it contains only six circuit elements) but dynamically the most complex among all non-linear circuits and systems described by a 21-parameter family of continuous odd-symmetric piecewise-linear vector fields. The third milestone is the recent discovery of several important new phenomena in Chua's circuits, e.g. stochastic resonance, chaos-chaos-type intermittency, 1/f noise spectrum, etc. These new phenomena could have far-reaching theoretical and practical significance. The fourth milestone is the theoretical and experimental demonstration that Chua's circuit can be easily controlled from a chaotic regime to a prescribed periodic or constant orbit, or it can be synchronized with two or more identical Chua circuits operating in an oscillatory or chaotic regime. These recent breakthroughs have ushered in a new era where chaos is deliberately created and exploited for unconventional applications e.g. secure communication.     

DLTS characterisation of InGaAlP films grown using different V/III ratios

Deep levels in InGaAlP films grown using two different V/III ratios have been studied by employing deep level transient spectroscopy (DLTS). The two samples investigated have the same composition of (Al_0.3Ga_0.7)_0.51In_0.49P and a film thickness of 0.6 μm, but grown with V/III ratios 75 and 50. Two defect levels with activation energies 0.23 and 0.78 eV are detected by temperature-scan DLTS in the sample with a V/III ratio of 75, with the 0.78 eV level being the dominant peak. Their respective capture cross-sections are 1.2×10⁻¹⁶ and 3.8×10⁻¹³ cm⁻². The 0.78 eV trap level is also analysed using isothermal DLTS measurement and similar values of thermal signatures are obtained. The DLTS spectrum of the 0.78 eV trap level has been found to be broader than that expected for a point-type defect, implying that it may be associated with a complex or extended defect. The observation of logarithmic capture mechanism further supports this speculation. On the other hand, no peak corresponding to the 0.23 eV level appears in isothermal DLTS spectra, which is possibly due to the severe temperature dependence of capture rate and the system's limitation in the high-frequency regime. For the sample with a V/III ratio of 50, only one dominant electron trap level, with an activation energy of 0.42 eV and a capture cross-section of 1.4×10⁻¹⁷ cm⁻², is detected by isothermal DLTS method.     

Voltage Unbalance Mitigation in Low Voltage Distribution Networks with Photovoltaic Systems

This paper proposes a technique to mitigate the voltage unbalance issue caused by the high penetration of photovoltaic(PV) systems into the low voltage distribution networks(LVDN) using a single phase energy storage system(ESS).The ESS comprises a bi-directional power flow inverter and a battery bank.The system is capable of absorbing the excess power and delivering power to the network in order to keep the voltage unbalance factor(VUF) below the statutory limit of 1%.Investigations are carried out in the experimental small-scale energy zone(SSEZ).The experimental results demonstrate that the ESS is capable of mitigating the VUF of the network.     

Regional changes in cerebral haemodynamics as a result of a visual stimulus measured by near infrared spectroscopy

Near infrared spectroscopy (NIRS) is used to measure global changes in cerebral haemodynamics. We have adapted the technique to measure regional changes in response to a visual stimulus. Ten volunteers were exposed to a computer generated visual stimulus designed to activate a large area of the visual cortex, including V1, V2, V3, V4 and V5. The stimulus was on for 30 s and off for 30 s. Changes in the concentrations of oxyhaemoglobin ([HbO2]) and deoxyhaemoglobin ([Hb]) were measured using a commercial spectrometer (NIRO500), over the occipital cortex. The data were summed over ten cycles. As a control, the experiment was repeated over the frontal cortex. For each subject [HbO2] increased during stimulation, and decreased when the stimulus was off. The mean (+/- s.e.m.) change in [HbO2] was 0.54 +/0 0.14 micromol 1(-1). The change in total haemoglobin concentration, given by [HbO2] + [Hb] was 0.61 +/- 0.21 micromol 1(-1), equivalent to a rise in cerebral blood volume of 0.04 +/- 0.01 ml 100 g(-1) which is about 2% of the total cerebral blood volume. There was no significant change in [HbO2] over the frontal cortex, implying that the changes in blood volume originated in the occipital lobe. This demonstrates that NIRS provides a non-invasive method of measuring regional changes in cerebral haemodynamics as a result of visual stimulation.     

Genital Group B Streptococcus carriage in the antenatal period: its role in prom and preterm labour

The authors report a case of pleural fibroma discovered during an examination for thoracic pains in a 65 year old woman. Histochemical studies were positive with vimentin and negative with KL1 antibodies and compatible with the most recent hypotheses concerning the purely fibroblastic origin of these tumours.     

Reversible amnesia associated with a left temporal hematoma in a case of right temporal complex partial seizures

We report the case of a 44-year-old woman with complex partial seizures (CPS) of right frontotemporal origin who developed generalized amnesia after undergoing intracranial electrode implantation complicated by left hippocampal hemorrhage. Serial memory testing disclosed recovery from the amnesic disorder, while repeated magnetic resonance imaging (MRI) showed resolution of her left hippocampal hemorrhage in a 2-month period. A second intracarotid amytal procedure confirmed the capability of her left temporal region to support memory. Consequently, a right orbitofrontotemporal lobectomy was performed without complication.