(Ba,Ca)TiO3 PTCR Ceramics with LaNiO3 Thin-Film Electrodes: Preparation and Characterization of the Interface

Conductive LaNiO₃ thin film electrodes were deposited by chemical solution deposition (CSD) from nitrate solutions onto polycrystalline Al₂O₃ and (Ba,Ca)TiO₃ PTCR ceramic substrates. The electrical properties of the LaNiO₃ thin film on Al₂O₃ and of the interface consisting of LaNiO₃ and the semiconductive oxide ceramic were investigated. The deposited LaNiO₃ films were about 250 nm thick and consisted of nanosized particles. The resistivity of the LaNiO₃ film was about 3 × 10^-3cm at 20°C. The PTCR ceramic consisted of m sized particles and exhibited an electronic resistivity of about 10 cm at 20°C and a steep increase of the resistivity of a few orders of magnitude above the Curie point at about 120°C. The electrical properties of the LaNiO₃/PTCR interface were dominated by the properties of a barrier layer between the PTCR ceramic and the LaNiO₃ electrode. The potential dependence of the impedance indicated that the barrier layer consisted of a depletion layer within the PTCR ceramic, when the flat band potential of LaNiO₃ on the PTCR ceramic at about –250 mV was exceeded. Additionally the formation of an insulating layer at the LaNiO₃ electrode has to be taken into account.     

Restoration of cardio-circulatory regulation by rate-adaptivepacemaker systems: the bioengineering view of a clinical problem

In the past, the development of rate-adaptive (sensor-controlled) pacemaker systems seems to have been determined primarily by the availability, compatibility and other properties of the technical sensor. This paper, however, focuses on the system-physiological aspect in an attempt to answer the question to what extent physiological cardiovascular control is restored by the pacemaker system. This is a question which should be asked before attempting to design a sensor-controlled system and especially before designing multisensor systems with infinite combinations. Four categories are defined: direct bridging ("shunting"), open loop systems, closed systems using cardiorespiratory or metabolic coupling and those using cardiac signals. Further subdivisions are shown. From the bioengineering as well as from the physiological viewpoint a system should preferably not combine sensors from one and the same of these categories. At present direct bridging is available only for the atrioventricular (AV)-block, so that for sick-sinus-syndrome (SSS) patients feedback control via cardiac signals ("inotropic" pacemaker) comes nearest the goal without, however, ideally bridging the gap. Open-loop systems should no longer be developed as single-sensor systems. A well developed activity sensor, however, which quickly pinpoints the most prominent stressor of cardiovascular control is best suited to complement another sensory system achieving closed-loop control. New and promising concepts orientated toward direct bridging are the analysis of monophasic action potentials and the "dromotropic" concept, both of which seek direct correlation with the "chronotropic" information not available in SSS patients.     

Emulsion-based fluorosensors for potassium featuring improved stability and signal change

A novel kind of potassium optode is presented which is based on the use of lipophilic droplets containing valinomycin and entrapped in a structured hydrogel. A positively charged solvatochromic dye located near the surface of the droplets responds to the valinomycin-assisted extraction of potassium from the sample by dramatic decrease of fluorescence intensity. The dynamic range is from 5 to 100 mM potassium, with negligible cross sensitivity to ionic strength. Cross sensitivity to pH is negligible too in the pH range from 6.5 to 7.3. The effect of interfering lipophilic anions is discussed. Response times within the dynamic range are less than 3 min on going from low to high potassium ion concentrations but about 10 min in the reverse direction. Response is fully reversible with only small drifts in baseline. The measurement uncertainty of determining 5 mM potassium is better than 0.2 mM.     

Fabrication of photonic crystal lasers by nanomolding of solgel glasses

We demonstrate the formation, in a single process step, of periodic arrays of features of surface relief with submicrometer lateral dimensions in hybrid organic and inorganic solgel glasses by using elastomeric molding techniques. Lasers formed with molded photonic crystal resonators that consist of triangular, square, and honeycomb lattices of cylindrical posts and holes show emission spectra and lasing thresholds that are similar to devices formed by conventional high-resolution photolithographic patterning of thick layers of thermally grown oxide.     

New Transient Hot-Bridge Sensor to Measure Thermal Conductivity, Thermal Diffusivity, and Volumetric Specific Heat

A high sensitivity thermoelectric sensor to measure all relevant thermal transport properties has been developed. This so-called transient hot bridge (THB) decidedly improves the state of the art for transient measurements of the thermal conductivity, thermal diffusivity, and volumetric specific heat. The new sensor is realized as a printed circuit foil of nickel between two polyimide sheets. Its layout consists of four identical strips arranged in parallel and connected for an equal-ratio Wheatstone bridge. At uniform temperature, the bridge is inherently balanced, i.e., no nulling is required prior to a run. An electric current makes the unequally spaced strips establish an inhomogeneous temperature profile that turns the bridge into an unbalanced condition. From then on, the THB produces an offset-free output signal of high sensitivity as a measure of the properties mentioned of the surrounding specimen. The signal is virtually free of thermal emf’s because no external bridge resistors are needed. Each single strip is meander-shaped to give it a higher resistivity and, additionally, segmented into a long and short part to compensate for the end effect. The THB closely meets the specific requirements of industry and research institutes for an easy to handle and accurate low cost sensor. As the key component of an instrument, it allows rapid thermal-conductivity measurements on solid and fluid specimens from 0.02 to 100 W· m⁻¹·K⁻¹ at temperatures up to 250°C. Measurements on some reference materials and thermal insulations are presented. These verify the preliminary estimated uncertainty of 2% in thermal conductivity.     

Direct coronary stenting without predilatation: a new therapeutic approach with a special balloon catheter design

Coronary stenting is the primary therapeutic option for many coronary lesions, after the risk of subacute stent thrombosis and bleeding complications has been reduced by antithrombotic regimens and improved stent expansion. It would be desirable to shorten the procedure and the duration of ischemia, and to reduce the risk of ischemic complications during balloon inflation by implanting the stent without previous dilatation of the lesion. This is not possible with the presently available stent delivery systems. This new therapeutic concept was tested with a specially designed balloon catheter, on which slotted-tube stents can be fixed between two conical radiopaque markers. Sixty-one patients eligible for angioplasty underwent direct stent implantation without predilatation. Four procedures were performed for acute myocardial infarction, and two as high-risk PTCA. Single slotted-tube stents (Palmaz-Schatz, NIR, or JOStent) of 14-16-mm length were mounted between the conical radiopaque markers of a special balloon which provided a fixation for the crimped stent. The direct implantation was successful in 80% of all patients, while in 10% the stent could be deployed after predilatation of the lesion. In 10% of lesions a stent could not be implanted with this and any other delivery system. When patients with successful direct stenting were compared with those with indirect (after predilatation) or unsuccessful stent deployment, the presence of angiographically visible calcification was higher in the unsuccessful cases (75% vs. 19%; P < 0.01), and the patients were older (72+/-8 vs. 61+/-12 years; P < 0.01). Radiation exposure time was only 8.7+/-5.1 min as compared with 12.6+/-7.6 min in conventional stent procedures with predilatation (P < 0.05). The number of balloons used per lesion was also lower than with conventional stenting. Stent dislocation was observed in 5%, and no embolization occurred. The new therapeutic approach of direct stenting without predilatation proved to be a safe and successful procedure in this initial series of coronary angioplasties. When calcified coronary lesions are avoided, it provides a way to rationalize stent implantation with shorter radiation exposure times, fewer balloons, and the potential advantage of fewer ischemic complications as no balloon predilatation is required.     

Secondary prevention of ischemic heart disease after coronary revascularization

This study was aimed to assess the compliance with policies for secondary prevention of coronary heart disease (CHD) one year after coronary artery revascularization with special attention to the management of hyperlipidemia. One year after coronary revascularization during the year 1994, patients were contacted by letter to determine the modification of their risk factors, the treatment patterns for hypercholesterolemia and to have their plasma lipid level and blood pressure measured. Of the 245 consecutive patients contacted (110 after coronary artery bypass grafting, and 135 after percutaneous transluminal coronary angioplasty), 186 (76%) provided the information required for further analysis. Excluding the patients older than 65 years, only 29 out of 97 patients (30%) with a total cholesterol of more than 5.2 mmol/l, and only 20 out of 52 patients (38%) with a total cholesterol of more than 6.2 mmol/l were receiving lipid lowering therapy 1 year after coronary artery revascularization. In contrast, 97% (n = 180) of the entire population studied were taking antiplatelet drugs and/or coumadine. Participation in an in-house rehabilitation program yielded a positive influence on smoking, but not on treatment of hypercholesterolemia. In conclusion, only a small proportion of patients with documented CHD and hypercholesterolemia were being treated for their lipid disorder 1 year after coronary artery revascularization. In contrast, the great majority of patients received antiplatelet and/or coumadine therapy: These results indicate that the compliance with published treatment guidelines for hyperlipidemia in patients with CHD is still highly inadequate, irrespective of the participation in a rehabilitation program.     

Predictors of aggressive behaviors: a longitudinal study in senior day care centers

Aggressive behaviors place elderly persons and their caregivers at risk. This study examines longitudinally the predictors of aggressive behaviors based on staff and family members' ratings of 200 community-dwelling participants from senior day care centers. The main difference between physically and verbally aggressive behaviors was found to be the role of physical and mental health. Cognitive impairment and poor quality of relationship were the main predictors of physically aggressive behaviors. Verbally aggressive behaviors were predicted mainly by depressed affect, low quality of relationships, and poor physical health. These results validate and expand prior cross-sectional research on the correlates of aggression in other populations, and guide in the development of interventions.