Showing papers by "Northwestern University published in 1976"

A survey of maintenance models: The control and surveillance of deteriorating systems

Abstract: The literature on maintenance models is surveyed. The focus is on work appearing since the 1965 survey "Maintenance Policies for Stochastically Failing Equipment: A Survey" by John McCall and the 1965 book", "The Mathematical Theory of Reliability", by Richard Barlow and Frank Proschan. The survey includes models which involve an optimal decision to procure, inspect, and repair and/or replace a unit subject to deterioration in service.

Sex Differences in the Games Children Play

Abstract: The world of play and games has been relegated to a minor position in the study of childhood socialization. This study accords a more important role in the socialization process to the games children play. It asks: are there sex differences in the organization of children's playtime activities? A large body of new empirical data on the leisure patterns of fifth-grade schoolchildren suggests six important differences. After describing these differences, the author speculates on their possible consequences. It is suggested that play and games contribute to the preservation of traditional sex-role divisions in society by equipping boys with the social skills needed for occupational careers while equipping girls with the social skills better suited for family careers.

Sedimentological and fluid-dynamic implications of the turbulent bursting phenomenon in geophysical flows

Abstract: The bursting process in turbulent boundary layers provides new insight on turbulence phenomena, mechanics of sedimentation, and genesis of bedforms in natural geophysical flows. Recent visualization experiments suggest that the turbulent boundary layer can be divided into an inner zone, whose essential characteristics scale with inner (wall) variables, and an outer zone, whose properties scale with the fluid-dynamic variables of the entire flow. The inner zone is distinguished by (i) a viscous sublayer displaying spanwise alternations of high-and low-speed streaks and (ii) episodic disruption by lift-ups of low-speed streaks. Oscillatory growth and breakup stages of the Stanford model of bursting characterize the turbulent structure of the outer zone. The burst cycle exists in turbulent boundary layers of all natural flows except perhaps (i) open-channel flows in the upper part of the upper flow regime and (ii) wind-generated surface waves. Fluid motions described as kolks and boils in incompressible open-channel flows correspond to the oscillatory growth stage and the late oscillatory growth and breakup stages, respectively, of the Stanford model of bursting. Supporting evidence includes (i) close similarity of gross fluid motions, (ii) equivalent scaling of boils and bursts, and (iii) intensification of boils and bursts in adverse pressure gradients and over rough beds. McQuivey's (1973) turbulence measurements show that the Eulerian integral time scale T E scales with the same outer variables as boil periodicity and burst periodicity. It is hypothesized that T E equals the mean duration of bursts at a point in the flow. Bedforms governed by the turbulent structure of the inner zone (microforms) cannot form if the sublayer is disrupted by bed roughness. The conditions for the existence of two common microforms and their spacings scale with the inner variables. Grain roughness increases the vertical intensity of the turbulence (by enhancing lift-ups) within the inner zone, thereby explaining textural differences between the coarse ripple and fine ripple bed stages of Moss (1972). Mesoforms respond to the fluid-dynamical regime in the outer zone and scale with the outer variables. The mean spacing of dunelike large-scale ripples in equilibrium open-channel flows is proportional to the boundary-layer thickness and equals the length scale formed by the product of the free-stream velocity and the boil period. Strong upward flow in a burst provides the vertical anisotropy in the turbulence which is needed to suspend sediment. Bursting promotes the entrain-ment of more and coarser sediment than tractive forces alone can accomplish.

Instability, Ductility, and Size Effect in Strain-Softening Concrete

Abstract: Analysis of structural instability due to strain-softening (ie, declining branch of the stress-strain diagram) is presented In a continuum, strain-softening is impossible; it can exist only in a heterogeneous material Failure occurs by unstable localization of strain or beam curvature, in which the stored strain energy of the structure is transferred into a small strain-softening region whose size is several times the aggregate size, or the spacing of reinforcement, or the depth of the beam The existence of a lower limit on the size of this region permits ductility, along with its dependence on the size and stored energy, to be predicted by a stability analysis Calculations of limit loads and moment redistributions in strain-softening beams and frames must include instability checks of possible curvature localization The same applies to finite element analyses of reinforced concrete structures with account of tensile cracking, and predictions of limit loads of these structures which are questionable because they depend on the size of the finite elements

Calculations of molecular ionization energies using a self‐consistent‐charge Hartree–Fock–Slater method

Abstract: A numerical-variational method for performing self-consistent molecular calculations in the Hartree-Fock-Slater (HFS) model is presented Molecular wavefunctions are expanded in terms of basis sets constructed from numerical HFS solutions of selected one-center atomlike problems Binding energies and wavefunctions for the molecules are generated using a discrete variational method for a given molecular potential In the self-consistent-charge (SCC) approximation to the complete self-consistent-field (SCF) method, results of a Mulliken population analysis of the molecular eigenfunctions are used in each iteration to produce 'atomic' occupation numbers The simplest SCC potential is then obtained from overlapping spherical atomlike charge distributions Molecular ionization energies are calculated using the transition-state procedure; results are given for CO, H2O, H2S, AlCl, InCl, and the Ni5O surface complex Agreement between experimental and theoretical ionization energies for the free-molecule valence levels is generally within 1 eV The simple SCC procedure gives a reasonably good approximation to the molecular potential, as shown by comparison with experiment, and with complete SCF calculations for CO, H2O, and H2S

Human colonic adenocarcinoma cells. I. Establishment and description of a new line.

Abstract: A series of human colonic epithelial cell lines have been cultured from a single patient: LS-180 the original adenocarcinoma, LS-174T a trypsinized variant, and normal colonic tissue. The malignant cells, 20 to 40, mum in diameter and oval to polygonal, exhibited characteristics of normal colonic mucosal cells, namely, abundant microvilli prominent in secretory cells, and the presence of intracytoplasmic mucin vacuoles. The cultured adenocarcinoma cells, but not normal, demonstrated neoplastic properties by producing high levels of carcinoembryonic antigen (CEA) and by the ability to be propagated in hamster cheek pouches and in immunodeprived mice. The CEA production by the newly established line LS-180 released 900 times more CEA per cell into the culture medium and bore 30 times more cell-associated material than the established line, HT-29. These cell lines may permit detection of distinctive chemical, physiological, pharmacologic, and immunologic characteristics of neoplastic colonic cells.

Control and Diabetes

Abstract: For almost 50 years, since insulin therapy was initiated, proponents of "rigid," "tight" or "chemical" control have quoted retrospective evidence of decreased or delayed nephropathy and retinopathy...

Hypertension screening of 1 million Americans. Community Hypertension Evaluation Clinic (CHEC) program, 1973 through 1975.

Abstract: During 1973 through 1975, more than 1 million persons were screened in the nationwide Community Hypertension Evaluation Clinic (CHEC) program at 1,171 sites. While those screened were not from defined populations, findings paralleled those of recent surveys of US population samples. First, CHEC confirmed the scope of the problem of elevated blood pressure in the United States. Of those screened, 247 of 1,000 had a diastolic reading of 90 mm Hg or higher; 116 of 1,000 had a reading of 95 mm Hg or greater. Prevalence of elevated blood pressure rose with age up to age 50 years, was higher in blacks than in whites, and was higher in men than in women. Second, CHEC data confirmed the challenge of undetected, untreated, and uncontrolled hypertension. Previously undetected hypertension was present in 27.7% of hypertensive people, detected but untreated in 10.7%, and treated but uncontrolled in 16.7%—totaling 55.1%. (JAMA235:2299-2306, 1976)

Structural Stability Theorems

Abstract: This chapter describes structural stability theorems. A C 1 (time independent) flow is a function f: R × M → M such that it has continuous first partial derivatives, for each t ∈ R f t : M → M is a diffeomorphism, and it satisfies the group property f t ° f s ( x ) = f t + s ( x ). The manifold M is assumed to be compact and without boundary. A neighborhood N of ƒ in the set of C 1 flows is those g such that g restricted to [0, 1] × M is uniformly near ƒ and all the first partial derivatives are uniformly near those of ƒ. The study of diffeomorphisms is the same as that for periodic time-dependent flows. Moreover, a neighborhood N of ƒ is those g that are uniformly near ƒ pointwise and whose first partial derivatives are uniformly near those of g . It can be said that ƒ satisfies the strong transversality condition if all stable manifolds of orbits that meet another unstable manifold of an orbit do so transversally.

Spindle cell carcinoma: ultrastructural evidence of squamous origin and collagen production by the tumor cells.

Abstract: Two cases of spindle cell carcinoma (SCC) of the esophagus and skin, respectively, were studied by transmission electron microscopy. The tumor cells were closely associated with collagen fibrils and had abundant rough endoplasmic reticulum with dilated cisternae. Except for their irregular shape and atypical nuclei they resembled actively synthesizing fibroblasts. In addition to these features, some cells contained numerous tonofibrils and occasional well-developed desmosomes. A gradual transition to typical squamous cells was noted in the skin tumor. These findings suggest that the pseudosarcomatous component of SCC originates from mesenchymal metaplasia of squamous cells and that collagen is produced by these metaplastic cells.

Milankovitch solar radiation variations and ice age ice sheet sizes

Abstract: The fluctuations in the size of ice age ice sheets are calculated using glacier mechanics and the Milankovitch solar radiation variations. The calculations are greatly simplified by considering only two-dimensional ice sheets with profiles that would be appropriate if ice obeyed the flow law of a perfectly plastic solid. The solar radiation variations seem to be large enough to account for ice ages.

Nurse Scheduling Using Mathematical Programming

Abstract: This paper formulates the nurse-scheduling problem as one of selecting a configuration of nurse schedules that minimize an objective function that balances the trade-off between staffing coverage and schedule preferences of individual nurses, subject to certain feasibility constraints on the nurse schedules. The problem is solved by a cyclic coordinate descent algorithm. We present results pertaining to a six-month application to a particular hospital unit and draw comparisons between the algorithm and hospital-generated schedules.

Theiler's Virus-Induced Demyelination: Prevention by Immunosuppression

Abstract: The effect of immunosuppression with cyclophosphamide and rabbit antiserum to mouse thymocytes on demyelination induced by Theiler's virus in SJL/J mice was ascertained from Epon-embedded sections (1 micrometer) of the central nervous system. Immunosuppression not only eliminated mononuclear cell infiltrates in the spinal cord white matter, but it also prevented the occurrence of demyelination. These results suggest that demyelination in this infection is immune-mediated.

Factors Influencing Innovation Success at the Project Level

Abstract: (1976). Factors Influencing Innovation Success at the Project Level. Research Management: Vol. 19, No. 3, pp. 15-20.

Mechanical properties of bone cements containing large doses of antibiotic powders

Abstract: The addition of up to 10 g gentamicin sulfate antibiotic powder to 60 g units of Simplex-P acrylic bone cement caused gradual, proportional decreases in the bulk muchanical properties of compressive and diametral tensile strengths. Water leaching of the antibiotic from the cement did not significnatly decrease these strenghts. Scanning electron microscopy (SEM) and energy-dispersive x-ray spectroscopy (EDS) showed the antibiotic to reside in the acrylic matrix as discrete particles not usually associated with internal porosity. The surface-sensitive flexural strength of a proprietary bone cement was lowered immediately by small quantities of antibiotic powder, and continued to decrease as doses of up to 10 g/unit were admixed. Water leaching caused channeling as the antibiotic was removed from the surface, but it did not create further changes in flexural strength.

Discrete subvalvular aortic stenosis in childhood. Study of 51 patients.

Abstract: Fifty-one children with discrete subvalvular aortic stenosis were studied between 1951 and 1974. The three anatomic types of obstruction found were the thin membranous type (43 cases), the fibromuscular collar type (5 cases) and the tunnel type (3 cases). The obstruction was usually severe, and the median left ventricular to aortic systolic pressure gradient was 90 mm Hg. Progressive obstruction with an increasing gradient was documented in 10 patients by serial cardiac catherizations. Significant associated cardiac defects, present in 57 percent of patients, often masked the typical clinical and cardiac catheterization features of subaortic stenosis. The stenosis was often not discovered until after surgery for the associated defect. Forty patients underwent surgical resection of the discrete subaortic obstruction. After surgery significant left ventricular to aortic pressure gradients can be found at postoperative cardiac catheterization. These gradients may reflect inadequate resection of the more complex discrete obstructions or represent proliferation and regrowth of the previously resected subvalvular fibrous tissue. The criteria for operability of discrete subaortic stenosis should be the angiographic demonstration of a discrete subvalvular diaphragm and the presence of a resting left ventricular to aortic systolic pressure gradient of 40 mm Hg or more.

Endochronic theory of inelasticity and failure of concrete

Abstract: A gradual accumulation of inelastic strain can be most conveniently described in terms of the so-called intrinsic time, whose increment depends on the time increment as well as the strain increments, and was previously developed for metals and is extended herein to concrete. It is demonstrated that the proposed model predicts quite closely: (1)Stress-strain diagrams for concretes of different strength; (2)uniaxial, biaxial, and triaxial stress-strain diagrams and failure envelopes; (3)failure envelopes for combined torsion and compression; (4)lateral strains and volume expansion in uniaxial and biaxial tests; (5)the behavior of spirally confined concrete; (6) hysteresis loops for repeated high compression; (7)cyclic creep up to 10 6 cycles; (8)the strain rate effect; (9)the decrease of long time strength; and (10)the increase of short-time strength due to low stress creep.

Thermal Contraction and Flexure of Mid-Continent and Atlantic Marginal Basins

Abstract: Summary Thermal contraction of the lithosphere is a probable cause of the gradual subsidence indicated by sediments of mid-continent basins and Atlantic continental shelves. The subsidence is complicated by time dependent regional isostatic compensation since adjacent parts of the lithosphere are mechanically coupled, and since creep in the lithosphere may relieve accumulated stress. Thus, if more subsidence occurs at point A than nearby point B, point A would be buoyed up and point B dragged down. Relaxation of this coupling during a later period of more gradual subsidence would produce uplift at B and downwarp at A. The absence of younger beds over local minima of subsidence such as the Florida arch, the flanks of the Michigan basin, and the Atlantic coastal plain (USA) can thus be explained. Variations in the subsidence rate due to exponential decay of the thermal anomaly or to starved basin-evaporite depositional sequences can produce observable effects. Analytic models of the Michigan basin and the Atlantic coast (USA) are compatible with previously estimated parameters: thermal decay time of the lithosphere, 50 My; flexural parameter of the lithosphere beneath air, 200 km; and viscosity of the lithosphere, 1025 poise. The effects of flexure are not clearly evident in Silurian evaporite deposition in the Michigan basin and it is probable that an extended time was required for the evaporite sequence to accumulate. The cause of the thermal heating event which precedes subsidence is unclear for mid-continent basins although bulk replacement of the uppermost mantle is necessary. The heating events may be associated with periods of slow sea-floor spreading (when slabs exert a tensional force on the lithosphere) and hence low eustatic sea level. There is little direct evidence that an initial heating event actually occurred in the Michigan basin immediately before the start of subsidence.

Fluctuating exchange rates and the pricing of exports

Abstract: The purpose of this paper is to examine the invoicing decision of an exporter under a system of pegged exchange rates and a system of freely fluctuating rates. With pegged exchange rates, the exporter may equivalently invoice in its home currency or in the currency of its foreign clients, since the two prices are related by the pegged rate. With fluctuating rates, however, the choice of an invoicing strategy is important and will affect the level of trade. The optimal prices with each strategy are compared, and the exporter's responses to governmental policy instruments are characterized.

The economics of multi-plant operation : an international comparisons study

Abstract: Why should manufacturing firms in many national industries maintain multiple small scale plants when they might produce the same output at a lower unit cost in a single large establishment? What specific benefits are attained through the operation of multiple plants? To address these questions, the authors conducted 125 in-depth interviews with businessmen actively involved in plant size and multi-plant operating decisions. They investigated the experience of twelve industries in six countries (West Germany, France, the United Kingdom, Sweden, Canada, and the United States).The authors develop an economic theory of plant size and multi-plant decisions and apply it to analyze the statistical and qualitative evidence on factors affecting plant size choices. They then examine the extent of multi-plant operation, its statistical correlate, and the economy actually or potentially realizable from various modes of multi-plant operation. Implications are drawn from antitrust and foreign trade policy, the evolution of scientific business management, and the development of industrial organization knowledge.