A Discrete-Time Approach to Stability Analysis of Systems With Aperiodic Sample-and-Hold Devices

Motivated by the widespread use of networked and embedded control systems, an algorithm for stability analysis is proposed for sampled-data feedback control systems with uncertainly time-varying sampling intervals. The algorithm is based on the robustness of related discrete-time systems against perturbation caused by the variation of sampling intervals. The validity of the algorithm is demonstrated by numerical examples.     

A Popov criterion for networked systems

We consider robustness analysis of heterogeneous and homogeneous networked systems based on integral quadratic constraints (IQCs). First, we show how the analysis decomposes into lower dimensional problems if the interconnection structure is exploited. This generally leads to a significant reduction of the computational complexity. Secondly, by considering a set of IQCs that characterizes the eigenvalues of the interconnection matrices of symmetrically networked systems, we derive a Popov-like criterion for such systems. In particular, when the nodes of the networked system are single-input–single-output linear time-invariant operators, the criterion can be illustrated using a generalized Popov plot. In such cases, the Popov criterion is also a necessary condition in the sense that if the criterion is violated then a destabilizing network with the specified eigenvalue distribution can be constructed.     

Surface modification of poly(ethylene terephthalate) by plasma polymerization of poly(ethylene glycol)

Poly(ethylene glycol) (PEG) was ‘polymerized’ onto poly(ethylene terephthalate) (PET) surface by radio frequency (RF) plasma polymerization of PEG (average molecular weight 200 Da) at a monomer vapour partial pressure of 10 Pa. Thin films strongly adherent onto PET could be produced by this method. The modified surface was characterized by infra red (IR) spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), cross-cut test, contact angle measurements and static platelet adhesion studies. The modified surface, believed to be extensively cross-linked, however showed all the chemical characteristics of PEG. The surface was found to be highly hydrophilic as evidenced by an interfacial free energy of about 0.7 dynes/cm. AFM studies showed that the surface of the modified PET became smooth by the plasma polymerized deposition. Static platelet adhesion studies using platelet rich plasma (PRP) showed considerably reduced adhesion of platelets onto the modified surface by SEM. Plasma ‘polymerization’ of a polymer such as PEG onto substrates may be a novel and interesting strategy to prepare PEG-like surfaces on a variety of substrates since the technique allows the formation of thin, pin-hole free, strongly adherent films on a variety of substrates.     

Visualizing vitreous using quantum dots as imaging agents

Vitreous is transparent tissue located between the lens and the retina of the eye, thus, difficult to look at by even ophthalmological microscope. But vitreous is connected with some sight-threatening eye diseases, for example, retinal detachment, macular hole, epi-retinal membrane, and so forth. Quantum dots (QDs) have been applied to a wide range of biological studies by taking advantage of their fluorescence properties. We established a novel technique of aqueous colloidal QD (ACQD) as a vitreous lesion detector. When compared with some conventional dyes used for clinical situation, i.e. fluorescein, indocyanine green, and triamcinolone acetonide, ACQD exerted a higher performance to detect a Weiss Ring. Furthermore ACQD is also effective to perform vitrectomy, an eye surgery to cut and eliminate vitreous. Some functional structures in vitreous are detected clearly when ACQD was injected into an enucleated porcine eye. We demonstrated that ACQD enabled any ophthalmic surgeon to perform vitrectomy reliably, easily, and more safely. Taken together, the ACQD-oriented vitreous staining system will promote ophthalmological science, and it will raise the cure rate of eye diseases     

Intracardiac ectopic thyroid mass

Intracardiac ectopic thyroid mass is an extremely rare occurrence. We describe a case of this rare disorder. The mass was clearly visualized by echocardiography, MRI, and cineangiography. The thyroid mass was excised successfully, and 50 months later the patient was well.     

A method for detecting service interactions

A method for detecting interactions among services and service features in communication systems is proposed. The method uses three types of knowledge: knowledge for clarifying and completing the specification of each feature, knowledge for identifying the implicit relationships among the features, and knowledge for detecting the interactions from the extended feature specifications derived from the first two types of knowledge. Six types of nontrivial interaction are outlined     

A bioassay for serum interferon based on induction of 2''5''-oligoadenylate synthetase activity

BACKGROUND: Patients treated for primary hyperparathyroidism run an increased risk of death. The aim of this study was to analyse several factors that may influence their risk of death. METHODS: General, laboratory, physical and clinical variables, altogether 34 variables, were defined as possible risk factors for death and were studied in a patient series of 845 patients operated on during the period 1953-82. Mean follow-up time was 10.5 years (SD 5.9); 253 patients were deceased at follow-up. Cox's proportional hazard model was used. RESULTS: We found seven variables with independent influence on the risk of death: age, sex, diabetes, cardiovascular disease, glomerular filtration rate, renal tubular concentration capacity and amount of diseased parathyroid tissue. The remaining 27 variables were separately tested, one at a time, using the same method and with the influence of age and sex eliminated. In this test situation, the year of surgery, peak serum calcium, serum creatinine level, body mass index, hypertension, psychiatric symptoms and a history of crisis were all significantly related to the risk of death. The analyses also gave information on the direction and magnitude of the effect of the variables on the risk of death. CONCLUSION: Primary hyperparathyroidism itself is a risk factor for death, but it was concluded that well-preserved renal function at surgery seems to have a protective role. We also found that the greater the amount of diseased parathyroid tissue the lesser the renal function and, furthermore, that hyperparathyroidism of substantial degree or long duration may bring about renal impairment that is not necessarily disclosed by the creatinine value alone.     

Shrinkage of liquid CO2 droplets in water

The shrinkage rate of liquid CO₂ droplets in water at 3°C was measured by the use of high-pressure vessel placed in a constant-temperature room. The change of the diameter of the droplet was observed at pressures of 28 MPa and 35 MPa using a time-lapse video camera. Bromocresol green was employed as a pH indicator, and was effective in monitoring the profile of carbonic acid distribution. When a droplet of liquid CO₂ was injected, CO₂ hydrate immediately formed and covered the surface of the droplet. The diameter of the liquid CO₂ droplet reduced gradually at a rate of 5.0 × 10^?7 m/s. It is predicted, from the viewpoint of ocean CO₂ sequestration, that a thin film of hydrate will form at the interface of sea water and liquid CO₂, and that the hydrate film will greatly control the dissolution of CO₂ into sea water.