Linear deterministic adaptive control: fundamental limitations?

This paper is concerned with the achievable performance of adaptive control algorithms. We show that when the only uncertainty is in the form of fixed parameter errors, then there exists an adaptive feedback law whose performance can be made arbitrarily close to that achievable when the system is a priori known. The result is not intended as a practical strategy. Instead, we use it to make the, perhaps obvious, point that meaningful results on performance of adaptive control algorithms must account for non-ideal factors including, at a minimum, noise, parameter time variations and unstructured uncertainty.     

Trabeculectomy function after cataract extraction

OBJECTIVE: To examine the effect of cataract extraction (CE) after trabeculectomy on intraocular pressure (IOP) control. DESIGN: Retrospective noncomparative case series. PARTICIPANTS: A total of 115 consecutive patients who underwent extracapsular CE (N = 58) or phacoemulsification (N = 57) with intraocular lens (IOL) placement after trabeculectomy were studied. INTERVENTION: Cataract extraction with IOL after trabeculectomy was performed. MAIN OUTCOME MEASURES: Preoperative, intraoperative, and postoperative factors were evaluated for association with loss of IOP control requiring additional medications, bleb needling, or further glaucoma surgery, using Kaplan-Meier survival analysis and Cox multivariate proportional hazards survival regression. RESULTS: After mean postoperative follow-up of 21.1 +/- 14.3 months, additional glaucoma medication or needling of the filtering bleb to maintain IOP control was required in 35 eyes (30.4%) and was significantly associated with intraoperative iris manipulation and early postoperative peak IOP greater than 25 mmHg. Additional glaucoma surgery was eventually required in 11 eyes (9.6%) and was significantly associated with age of 50 years or younger, preoperative IOP greater than 10 mmHg, and early postoperative peak IOP greater than 25 mmHg. The cumulative proportion of patients who did not require reoperation for glaucoma was 93% and 90% at 1 and 2 years, respectively. The mean IOP at last visit had increased 1.6 mmHg above the pre-CE level and did not vary significantly after the first postoperative month. The median interval from CE to the addition of glaucoma medication or bleb needling was 1.6 months (within 3 months in 20 of 33 eyes) and that from nonsurgical intervention to further glaucoma surgery was 3.6 months (before the 7th postoperative month in 6 of 11 eyes). Of 19 eyes with hypotony (IOP < or = 6 mmHg) before CE, 11 eyes remained hypotonous after CE despite an increase in the mean IOP from 4.6 to 7.5 mmHg. CONCLUSIONS: When CE is performed after trabeculectomy, age of 50 years or younger, preoperative IOP greater than 10 mmHg, intraoperative iris manipulation, and early postoperative IOP greater than 25 mmHg are associated with worsened postoperative IOP control. Most bleb failures occur soon after CE. Resolution of pre-existing hypotony after CE is unpredictable.     

Parametric cure models of relative and cause-specific survival for grouped survival times

With parametric cure models, we can express survival parameters (e.g. cured fraction, location and scale parameters) as functions of covariates. These models can measure survival from a specific disease process, either by examining deaths due to the cause under study (cause-specific survival), or by comparing all deaths to those in a matched control population (relative survival). We present a binomial maximum likelihood algorithm to be used for actuarial data, where follow-up times are grouped into specific intervals. Our algorithm provides simultaneous maximum likelihood estimates for all the parameters of a cure model and can be used for cause-specific or relative survival analysis with a variety of survival distributions. Current software does not provide the flexibility of this unified approach.     

High-speed enhancement-mode InP MISFET's grown by chloridevapor-phase epitaxy

The properties of enhancement-mode InP metal-insulator-semiconductor field-effect transistors fabricated on semi-insulating InP substrates are reported. The epitaxial layers of the device structure have been grown by chloride vapor-phase epitaxy. Short-circuit current gain cutoff frequencies of 29.6 GHz were measured for 1-μm-gate-length devices. For devices with submicrometer gate lengths, extrinsic transconductance values up to 300 mS/mm and short-circuit current-gain cutoff frequencies of 38.1 GHz were measured. SiO₂ deposited by electron beam evaporation and plasma-enhanced CVD Si₃N₄ have been utilized as gate insulators, and a drain current drift of 30% within the first 50 h of operation has been observed. The high-speed performance of these devices represent to the authors' knowledge the fastest InP-based MIS field-effect transistor demonstrated     

Robust Patterns in Recurrent Sampling of Multiband Signals

Periodic nonuniform sampling can be used to achieve sub-Nyquist sampling of bandlimited multiband signals. In this paper, we examine the question of selecting the sampling pattern in such a scheme, so that the reconstruction robustness - measured by the condition-number of the modulation matrix - is maximized. Contrary to previous work, where the sampling pattern was chosen from a discrete set, we let the sampling patterns vary continuously, but impose a structural constraint. Using this approach, we derive necessary and sufficient conditions on the spectral support of the signal for which perfect conditioning exist, namely, for which a sampling pattern can be found so that the resulting modulation matrix has a condition number equal to 1. A simple test to check for these conditions is developed and the desired sampling patterns are found. An algorithm for choosing the sampling pattern when the aforementioned conditions are not satisfied is also introduced. Finally, we present some simulation results.     

Interpretation of intraocular and serum antibody levels in necrotizing retinitis

BACKGROUND: Intraocular antibodies have been measured as a diagnostic aid in necrotizing retinitis but interpretation of results may be difficult. METHODS: Vitreous or aqueous and serum immunoglobulin G antibodies to toxoplasmosis, cytomegalovirus, herpes simplex virus I and II, and varicella zoster virus were subjected to enzyme-linked immunosorbent assay in 27 patients with necrotizing retinitis and 15 control patients. A quotient was derived quantitating the amount of excess antibody in the eye compared to serum. Different interpretative rules were analyzed to determine which yielded the highest sensitivity and specificity. RESULTS: The highest intraocular antibody relative to serum among the 4 antibodies correctly predicted the final clinical diagnosis in 21 of 27 patients, for a sensitivity of 78% and a specificity of 90%. Interpretive rules that relied on a high numeric value of the antibody quotient or did not consider the relative ranking of the four antibody quotients were less sensitive and specific because multiple antibodies were detected in most eyes. The technique was safe and rapid. CONCLUSION: Interpretation of antibody titers in intraocular fluids is facilitated by testing several relevant antibodies and comparing the results. The technique may be helpful to diagnose necrotizing retinitis and to ascertain viral cause in acute retinal necrosis.