Quadratic stabilizability of uncertain linear systems: Existence of a nonlinear stabilizing control does not imply existence of a linear stabilizing control

This note is concerned with the problem of stabilizing an uncertain linear system via state feedback control. An uncertain system which admits a stabilizing state feedback control and some associated quadratic Lyapunov function is said to be quadratically stabilizable. In a number of recent papers, conditions are given under which quadratic stabilizability via nonlinear control implies quadratic stabilizability via linear control. These papers restrict the manner in which the uncertain parameters are permitted to enter structurally into the state equation in order to establish this result. This note presents an example which shows that this implication is not true for more general uncertain linear systems. To this end, we describe an uncertain linear system which is quadratically stabilizable via nonlinear control but not quadratically stabilizable via linear control.     

A Riccati equation approach to the design of stabilizing controllers and observers for a class of uncertain linear systems

This paper presents a procedure for designing a full state observer and feedback control law which will stabilize a given uncertain linear system. The uncertain linear systems under consideration are described by state equations which depend on uncertain parameters. These uncertain parameters may be time varying. Their values, however, are constrained to lie within known compact bounding sets. The design procedure involves solving two algebraic Riccati equations. A feature of the design procedure presented is the fact that it reduces to the standard LQG design procedure if the system contains no uncertain parameters.     

Lesion location influences perception of homonymous scotomata during flickering random dot pattern stimulation

An attempt was made to clarify whether the site of postchiasmal lesions affects subjective perception of homonymous visual field defects during stimulation with flickering random dot patterns (white noise-field). Out of 56 patients with homonymous hemianopia, 38 (68%) perceived scotomata in this situation, but 18 (32%) discerned none at all. Neuroradiologic superposition of cerebral lesions detected by computed tomography (CT) or magnetic resonance imaging (MRI) showed that nearly all patients who perceived their scotomata had lesions involving the primary visual cortex or the perigeniculate region, whereas those who received no scotoma had lesions centered within the optic radiation. Functional MRI of six normal subjects during stimulation with flickering random dot patterns indicated predominant activation of the primary visual cortex. Since noise-field defects were most frequently perceived by patients whose lesion involved the primary visual cortex, it appears that the sensitivity of noise-field campimetry depends on the site of damage in the visual pathway. The explanation for this may be that damage to long-range horizontal connections impairs filling-in processes.     

Tissue phenotype depends on reciprocal interactions between the extracellular matrix and the structural organization of the nucleus

What determines the nuclear organization within a cell and whether this organization itself can impose cellular function within a tissue remains unknown. To explore the relationship between nuclear organization and tissue architecture and function, we used a model of human mammary epithelial cell acinar morphogenesis. When cultured within a reconstituted basement membrane (rBM), HMT-3522 cells form polarized and growth-arrested tissue-like acini with a central lumen and deposit an endogenous BM. We show that rBM-induced morphogenesis is accompanied by relocalization of the nuclear matrix proteins NuMA, splicing factor SRm160, and cell cycle regulator Rb. These proteins had distinct distribution patterns specific for proliferation, growth arrest, and acini formation, whereas the distribution of the nuclear lamina protein, lamin B, remained unchanged. NuMA relocalized to foci, which coalesced into larger assemblies as morphogenesis progressed. Perturbation of histone acetylation in the acini by trichostatin A treatment altered chromatin structure, disrupted NuMA foci, and induced cell proliferation. Moreover, treatment of transiently permeabilized acini with a NuMA antibody led to the disruption of NuMA foci, alteration of histone acetylation, activation of metalloproteases, and breakdown of the endogenous BM. These results experimentally demonstrate a dynamic interaction between the extracellular matrix, nuclear organization, and tissue phenotype. They further show that rather than passively reflecting changes in gene expression, nuclear organization itself can modulate the cellular and tissue phenotype.     

Measurement of equivalent power density and RF energy deposition inthe immediate vicinity of a 24-GHz traffic radar antenna

In response to reports of alleged health effects associated with the use of hand-held traffic radars, e.g., testicular cancer, a study was undertaken to quantify: (1) the distribution of the electric field (E) in the immediate vicinity of the antenna aperture of a typical 24-GHz hand-held traffic radar; and (2) the relative match and the corresponding depth of penetration of the absorbed energy when the antenna aperture is positioned in contact with material having properties similar to human tissue. The former measurements are important for assessing a large number of measurements reported by others using techniques that are not expected to be reliable indicators of power density at distances small compared with the size of the radiator; the latter are important for verifying predictions that energy from the antenna at 24-GHz will be predominantly absorbed in superficial tissue, i.e., the skin. The results of the first part of the study indicate that the equivalent-plane-wave power density in the plane of the aperture of the radar antenna is approximately one-half of the corresponding values reported in the literature; the results of the second part of the study indicate that the depth of penetration into material simulating human skin is approximately 0.5 mm     

Pathologic seminal vesicle invasion after radical prostatectomy for patients with prostate carcinoma: effect of early adjuvant radiation therapy on biochemical control

BACKGROUND: The authors evaluated the effect of postoperative radiation therapy on freedom from biochemical failure (bNED) in men with prostate carcinoma who had pathologic seminal vesicle invasion after radical prostatectomy and negative pelvic lymph node dissection (pT3cN0). METHODS: Between 1989 and 1995, 375 men underwent radical prostatectomy at Thomas Jefferson University Hospital. Fifty-three men (13%) had pT3cN0 prostate carcinoma and were the subject of this analysis. Men in whom prostate specific antigen (PSA) could not be detected were deemed free of biochemical failure. RESULTS: Of the 53 men with pT3cN0 prostate carcinoma, 18 had an elevated PSA immediately after surgery and received salvage radiation therapy (RT). The 3-year bNED rate for this group was only 38%. At 3 months, PSA could not be detected in the other 35 men. Fifteen of those 35 men underwent early adjuvant RT, and the other 20 were observed for biochemical failure. The 3-year bNED rate for the 15 patients treated with immediate adjuvant RT was 86%, compared with 48% for the 20 men who were observed (P = 0.01). CONCLUSIONS: These data suggest that early adjuvant RT for men with pT3cN0 prostate carcinoma and no detectable PSA postoperatively reduces the likelihood of future biochemical failure. Men with pT3cN0 prostate carcinoma and a persistently elevated postoperative PSA level are less likely to benefit from RT and should be considered for systemic therapy.     

Influences of environmental conditions during infancy on final body stature

In the following article we shall investigate the Second World War with its consequences on nutrition and other living conditions for the German population to try to determine whether lack of nutrition plus other deficiencies, which infants were subjected to in Germany during this time, had any influence on their adult stature. The following data formed the basis of our investigation: (1) nutrition of infants and school-aged children during the years 1939-1948; (2) stature and weight of 6-year-old boys between 1907 and 1948; (3) infant mortality between 1935 and 1950; (4) stature of 19-year-old men who were born between 1938 and 1951. From Figure 5 it can be seen that the mean stature of 19-year-old men born between 1938 and 1951 (except for those born in 1944 and 1945) rose steadily (secular acceleration). The plot of the yearly rate of acceleration (Fig. 6) reveals a minimum in 1944-1945, and follows a general downward, U-shaped trend (P less than 0.05). On the other hand, infant mortality between 1941 and 1949 follows an upward U-shaped trend (P less than 0.05). For the 6- to 8-month-old infants during 1945-1948 nutrition was far worse than that during the preceding years. It is even likely that the nutrition for the infants had already begun to decrease in quality in 1942. We find, therefore, a close correlation between the years of high infant mortality and the growth deficiencies of the men born during these years. Since we must assume that the nutritional situation for babies and infants worsened steadily after 1942 until it is apparent that a number of environmental factors directly influence human growth. The conclusion of our analysis is that a deficit of growth occurring after the end of the fourth year can be compensated fully. We conclude, furthermore, that the growth deficits which arise before the fourth year, on the other hand, cannot be compensated fully even if good or excellent environmental conditions follow.     

Stochastic response of offshore towers to random sea waves and strong motion earthquakes

Presented is a stochastic method of analysis of offshore towers subjected separately to random sea waves and to strong motion earthquakes. The Pierson-Moskowitz wave height spectrum is used along with linear wave theory to define a stationary random sea state as caused by wind generated surface waves. A zero mean ergodic Gaussian process of finite duration is used to characterize horizontal ground acceleration caused by strong motion earthquakes. For each type of loading, full fluid structure interaction effects are included in stochastic analysis. Numerical results for 4 representative deep water towers having heights of 475, 675, 875 and 1,075 feet are presented. Particular emphasis is placed on the maximum or extreme values of total transverse shear and total overturning moment versus elevation above the base of each tower. The results of the earthquake analysis are compared with corresponding design code values and the role of ductility is briefly discussed.     

Optically pumped FIR lasers: Frequency and power measurements and laser magnetic resonance spectroscopy

Optically pumped FIR lasers are currently in use in both frequency metrology and laser magnetic resonance spectroscopy programs in the NBS Boulder labs. The laser for use in frequency metrology is a CW 71 μm methyl alcohol waveguide laser with over 100 mW output for frequency synthesis. Another laser with an intracavity absorption cell for laser spectroscopy has been constructed and is nearly transversely pumped. The metrology technique used to measure the frequency of these lasers is briefly reviewed and a unique power meter is described.     

The FT-30 seawater reverse osmosis membrane--element test results

A thin-film composite reverse osmosis (RO) membrane has been developed that provides excellent performance when used in single-pass seawater systems. This membrane, designated FT-30, gives superior performance in such areas as flux, salt rejection, chemical stability, and microbiological resistance. In addition, it is resistant to some oxidizing disinfectant agents, although it is not fully resistant to chlorine; elements fabricated from the membrane have shown damage after 2,000 to 2,500 hours exposure to seawater at 0.5 milligrams per liter (mg/l) active chlorine. It appears that the membrane can operate continuously at active chlorine concentrations below 0.2 mg/l.Several long-term studies were carried out at the OWRT Wrightsville Beach Test Facilities. In actual trials in seawater systems, salt rejections as high as 99.5 percent and fluxes of 23 gfd have been obtained when tested at 800 psi and 25°C. Some of the elements have been in continuous operation for over 4, 000 hours with no deterioration in salt rejection and with only the normal flux decline usually associated with compaction and scaling. Other elements have been installed in small seawater systems with normal intermittant use for almost two years with no serious loss in performance.