Showing papers by "Northwestern University published in 1974"

Structure-Borne Sound

Abstract: Although sound waves in structures cannot be heard directly, and only be felt at low frequencies, they play an important role in noise control, because many sound signals are generated or transmitted in structures before they are radiated into the surrounding medium. In several respects sound waves in structures and sound waves in gases or liquids are similar, there are, however, also fundamental differences, which are due to the fact that solids have a certain shear stiffness, wheras gases or liquids show practically none. As a consequence acoustic energy can be transported not only by the normal compressional waves but also by shear waves and many combinations of compressional (sometimes loosely called longitudinal) and shear waves . For noise control purposes bending waves (which are a special combination of compressional and shear waves) are of primary importance; for some special cases (quasi-) longitudinal waves and torsional waves also have to be considered.

Overinsurance and Public Provision of Insurance: The Roles of Moral Hazard and Adverse Selection

Abstract: Publisher Summary This chapter discusses overinsurance and public provision of insurance. In the absence of perfect information, the competitive outcome in markets for insurance may be nonoptimal not only compared to the infeasible optimum that would have occurred if information were perfect but also compared to optima that are feasible. If the government had or could obtain perfect information about the purchase-date state of the world, it could in principle provide the optimal insurance or at least achieve a result superior to that of the imperfectly informed market. The chapter presents a case in which the insurance purchaser has control over actions in the present that affect the future state of nature but in which the insurer cannot directly observe the insured's actions. An optimal solution in this kind of a moral hazard situation is for the insured to retain some part of his losses. Thus, the optimal policy is one that achieves the optimal trade-off between the conflicting goals of furthering risk spreading and providing appropriate incentives.

Stability of the junction of an ice sheet and an ice shelf

Abstract: An analysis is made of the steady-state size of a two-dimensional ice sheet whose base is below sea-level and which terminates in floating ice shelves. Under the assumption of perfect plasticity it is found that an ice sheet placed on a bed whose surface was initially flat cannot exist if the depth of the bed below sea-level exceeds a critical depth. If this depth is less than the critical level, the ice sheet extends out to the edge of the continental shelf. Similar results are found with more realistic assumptions about the laws governing the flow of ice. If the bed slopes away from the centre, the ice sheet can have a stable width that increases in value as the accumulation rate increases or as sea-level is lowered. It is not possible to decide whether or not the West Antarctic ice sheet is in stable equilibrium. It is entirely possible that this ice sheet is disintegrating at present, as suggested by Hughes.

Characterization of Connection Assignment of Diagnosable Systems

Abstract: Preparata, Metze, and Chien [1] gave necessary conditions for identification of all faulty units in a system S capable of automatic fault diagnosis. We show that these conditions are sufficient if in S no two units test each other. Necessary and sufficient conditions are also obtained for the general case when no such restriction is placed on S.

Persistence and Change in Political Systems, 1800–1971

Abstract: This study reports the codification of basic authority characteristics of 336 national political systems (polities) that functioned in 91 nation-states between 1800 and 1971. In form the typical 19th-century polity was an autocracy with minimal functions. Its 20th-century counterpart was either an activist plural democracy or an activist autocracy. The incidence of system-transforming political change has been equally high and pervasive in both European and Third-world polities, but greater in the 20th century than the 19th. The data are used to test three hypotheses that attribute the persistence and adaptability of political systems to their authority characteristics. “Institutionalization” arguments about the stability-enhancing effects of complexity and directiveness receive no consistent support. Conventional beliefs about the greater durability of democracies vs. autocracies vs. anocracies (uninstitutionalized polities) are confirmed only in Europe in the 20th century. The most durable historical and Afro-Asian polities have been either autocratic or anocratic. The data generally support the hypothesis that “pure” political systems—consistently democratic or consistently autocratic—are more durable than systems of mixed authority characteristics. Long-term trends in political “development” and their determinants are discussed in the light of the findings.

Munchausen's stridor: non‐organic laryngeal obstruction

Abstract: Summary A patient had at least 15 hospital admissions for symptoms of acute dyspnoea accompanied by loud stridorous sounds. These episodes had been diagnosed as acute airway obstruction and she was treated on all occasions on an emergency basis. In the absence of a definitive etiology and with other clues, it was then recognized that the patient was imitating the clinical appearance of laryngeal obstruction. Following the establishment of this, psychiatric care was initiated with the goal of rehabilitation of the patient, and there have been no further episodes to the present time.

Rate-type creep law of aging concrete based on maxwell chain

Abstract: It is shown that the linear creep law of concrete can be characterized, with any desired accuracy, by a rate-type creep law that can be interpreted by a Maxwell chain model of time-variable viscosities and spring moduli. Identification of these parameters from the test data is accomplished by expanding into Direchlet series the relaxation curves, which in turn are computed from the measured creep curves. The identification has a unique solution if a certain smoothing condition is imposed upon the relaxation spectra. The formulation is useful for the step-by-step time integration of large finite element systems because it makes the storage of stress history unnecessary. For this purpose a new, unconditionally stable numerical algorithm is presented, allowing an arbitrary increase of the time step as the creep rate decays. The rate-type formulation permits establishing a correlation with the rate processes in the microstructure and thus opens the way toward rational generations to variable tempeature and water content. The previously developed Kelvin-type chain also permits such a correlation, but its identification from test data is more complicated.

Consumer Assessments of the Quality of Medical Care

Abstract: Studies using consumer evaluations of the quality of medical care are reviewed. Important methodological issues in studies using this approach are discussed and future paths for research are presented.

Some exact solutions of Einstein field equations

Abstract: We obtain exact exterior solutions of a rotating infinite cylinder. In addition to two different solutions obtained before, a new solution is found which is finite on the axis. It seems that these three solutions exhaust the possibilities.

Unit Refutations and Horn Sets

Abstract: The key concepts for this automated theorem-proving paper are those of Horn set and strictly-unit refutation. A Horn set is a set of clauses such that none of its members contains more than one positive literal. A strictly-unit refutation is a proof by contradiction in which no step is justified by applying a rule of inference to a set of clauses all of which contain more than one literal. Horn sets occur in many fields of mathematics such as the theory of groups, rings, Moufang loops, and Henkin models. The usual translation into first-order predicate calculus of the axioms of these and many other fields yields a set of Horn clauses. The striking feature of the Horn property for finite sets of clauses is that its presence or absence can be determined by inspection. Thus, the determination of the applicability of the theorems and procedures of this paper is immediate.In Theorem 1 it is proved that, if S is an unsatisfiable Horn set, there exists a strictly-unit refutation of S employing binary resolution alone, thus eliminating the need for factoring; moreover, one of the immediate ancestors of each step of the refutation is in fact a positive unit clause. A theorem similar to Theorem 1 for paramodulation-based inference systems is proven in Theorem 3 but with the inclusion of factoring as an inference rule. In Section 3 two reduction procedures are discussed. For the first, Chang's splitting, a rule is provided to guide both the choice of clauses and the way in which to split. The second reduction procedure enables one to refute a Horn set by refuting but one of a corresponding family of simpler subproblems.

Pulmonary vascular disease in complete transposition of the great arteries: a study of 200 patients.

Abstract: Lung specimens of 200 patients with transposition of the great arteries were examined microscopically for evidence of pulmonary vascular disease. In patients with an intact ventricular septum or a small ventricular septal defect, advanced pulmonary vascular disease was uncommon; only 9 of 107 such patients (8.4 percent) demonstrated greater than grade 2 (Heath-Edwards) pulmonary vascular disease. A persistent large patent ductus arteriosus appeared to promote progressive pulmonary vascular disease in this group since each of the five infants less than 1 year of age with grade 3 or 4 disease had this lesion. In contrast, pulmonary vascular disease was common in patients with a large ventricular septal defect; 37 of 93 patients (40 percent) with this defect had greater than grade 2 pulmonary vascular disease. Among patients more than 1 year of age, 26 of 35 (75 percent) had grade 4 disease. The catheterization data suggest that the calculated pulmonary vascular resistance may underestimate the degree of disease, probably by overestimating the pulmonary blood flow (Fick method). Pulmonic stenosis appeared to protect the lungs from progressive pulmonary vascular disease, and pulmonary arterial banding was protective when performed before age 6 months. Our studies indicate that a persistent large patent ductus arteriosus should be closed as early as possible in view of its association with advanced pulmonary vascular disease in these patients. In infants with a large ventricular septal defect, pulmonary arterial banding or corrective surgery with closure of the defect should be performed between the ages of 4 and 6 months to prevent progressive pulmonary vascular damage.

Serum IgE concentration in atopic dermatitis. Relationship to severity of disease and presence of atopic respiratory disease.

Abstract: A survey was conducted to evaluate the serum IgE concentrations of 58 patients with atopic dermatitis of varying severity and activity. The determination of serum IgE concentrations does not provide a diagnostic criterion for atopic dermatitis because 57% of the patients had levels of IgE considered to be within a normal range. When serum IgE concentrations are elevated in atopic dermatitis, this is associated with an increased severity of the disease, with coexistent atopic respiratory disease or with both. This association may have relevance to the pathogenesis of the respiratory disease, which is IgE-mediated, the severity of the dermatitis, or both. The manner in which this may occur, if there is more than a coincidental relationship, is uncertain.

Mechanical properties of human cancellous bone in the femoral head.

Abstract: The ultimate compressive strength of human cancellous bone derived from femoral heads was found to range between 21 and 1963 Ibf/in2 (145-13535 kN/m2). A correlation coefficient of 0·70 was found for the relationship between compressive strength and apparent density of cancellous bone; however, no statistically significant correlation was found between compressive strength and location of the cancellous bone within a femoral head. The stress relaxation of cancellous bone, measured at widely differing initial stresses, demonstrates the viscoelastic nature of cancellous bone, and consequently the tendency to flow or creep under time-dependent stresses.

Mode-locked laser Raman spectroscopy. New technique for the rejection of interfering background luminescence signals

Abstract: st ra te the applicability of the TFV-ICP system to the analysis of samples over a n extended concentration range. T h e curve covers the four-decade concentration range of 0.001 to 10 fig Be/ml or from 2.5 X 10-11 t o 2.5 x 10-7 gram of Be. Discussion. A comparison of the TFV-ICP detection limits reported in Table I1 with t h e best values so far reported for the introduction of nebulized solution into the plasma shows t h a t the TFV-ICP system is superior by 1 to 2 orders of magnitude. This appears to be the result of the increased concentration of the analyte, already desolvated and vaporized by the filament, passing through the axial channel of the plasma per unit t ime. T h e same mechanism is utilized in AAS and AFS when filament vaporization is performed, bu t for these techniques, the free a toms must be produced a t the filament surface whereas for the plasma system it is only necessary to vaporize the analyte elements; the dissociation and excitation occur in the plasma. t /i' 1 0 U d oooo1 0001 0 01 01 10 10 0 Concentration (+Q B c l m l )

SYNAPTIC VESICLE DEPLETION AND RECOVERY IN CAT SYMPATHETIC GANGLIA ELECTRICALLY STIMULATED IN VIVO: Evidence for Transmitter Secretion by Exocytosis

Abstract: This study examined the ultrastructure of presynaptic terminals after short periods of vigorous acetylcholine (ACh) secretion in the cat superior cervical ganglion in vivo. Experimental trunks of cats anesthetized with chloralose-urethane were stimulated supra-maximally for periods of 15–30 min and at several frequencies including the upper physiological range (5–10 Hz). Stimulated and contralateral control ganglia from each animal were fixed by intra-arterial aldehyde perfusion, processed simultaneously, and compared by electron microscopy. Stimulation produced an absolute decrease in the number of synaptic vesicles, an enlargement of axonal surface membrane, and distinct alterations in the shape of presynaptic terminals. Virtually complete recovery occurred within 1 h after stimulation at 10 Hz for 30 min. These results support the hypothesis that ACh release at mammalian axodendritic synapses occurs by exocytosis of synaptic vesicles resulting in the incorporation of vesicle membrane into the presynaptic membrane and that synaptic vesicles subsequently are reformed from plasma membrane.