Showing papers by "Harvard University published in 1971"

Dynamic models of segregation

Abstract: Some segregation results from the practices of organizations, some from specialized communication systems, some from correlation with a variable that is non‐random; and some results from the interplay of individual choices. This is an abstract study of the interactive dynamics of discriminatory individual choices. One model is a simulation in which individual members of two recognizable groups distribute themselves in neighborhoods defined by reference to their own locations. A second model is analytic and deals with compartmented space. A final section applies the analytics to ‘neighborhood tipping.’ The systemic effects are found to be overwhelming: there is no simple correspondence of individual incentive to collective results. Exaggerated separation and patterning result from the dynamics of movement. Inferences about individual motives can usually not be drawn from aggregate patterns. Some unexpected phenomena, like density and vacancy, are generated. A general theory of ‘tipping’ begins to emerge.

Isolation of a tumor factor responsible for angiogenesis

Abstract: Human and animal solid tumors elaborate a factor which is mitogenic to capillary endothelial cells. This factor has been called tumor-angiogenesis factor. The important components of TAF are RNA and protein. It is suggested that blockade of this factor (inhibition of angiogenesis) might arrest solid tumors at a tiny diameter of a few millimeters.

Structural equivalence of individuals in social networks

Abstract: The aim of this paper is to understand the interrelations among relations within concrete social groups. Social structure is sought, not ideal types, although the latter are relevant to interrelations among relations. From a detailed social network, patterns of global relations can be extracted, within which classes of equivalently positioned individuals are delineated. The global patterns are derived algebraically through a ‘functorial’ mapping of the original pattern. Such a mapping (essentially a generalized homomorphism) allows systematically for concatenation of effects through the network. The notion of functorial mapping is of central importance in the ‘theory of categories,’ a branch of modern algebra with numerous applications to algebra, topology, logic. The paper contains analyses of two social networks, exemplifying this approach.

Neuron‐glia relationship during granule cell migration in developing cerebellar cortex. A Golgi and electonmicroscopic study in Macacus rhesus

Abstract: The cytology of the postmitotic migratory granule cell and its relationship to Bergmann glial processes was examined with Golgi staining and electron microscopy in the three cardinal planes in the developing cerebellar cortex of Macacus rhesus at various late fetal and early postnatal ages. After final mitosis the granule cell body transforms from a nearly round shape in the superficial zone of the external granular layer to a horizontal bipolar form with elongated processes oriented longitudinally to the folium, at the outer border of the molecular layer. Another descending process develops, and the cell soma becomes a pyramid flattened in the plane longitudinal to the folium. The nucleus moves into the descending process and the cell soma assumes a vertically oriented spindle shape while migrating among previously formed parallel fibers deeper in the molecular layer, and finally attains a round shape again when it lies deep to the Purkinje cell layer. During these transformations, the cell cytoplasm becomes more voluminous and contains a prominent Golgi apparatus, numerous free ribosomes, mitochondria, multivesicular and dense bodies, and fascicles of microtubules Longitudinally oriented microtubules concentrated in the vertical leading process disappear by the time the cell soma enters the granular layer. The slender trailing process loss most of its cytoplasmic organelles, acquires microtubules and together with the horizontal processes forms the characteristic T-shaped axon. The axon forms synapses with Purkinje and stellate cell dendrites at a time when other granule cells are still migrating among them. During the entire course of their migration across the molecular layer, granule cells are directly apposed to vertically oriented Bergmann fibers belonging to the Golgi epithelial cells. The sequence of developmental stages indicates that Golgi epithelial cells are a type of protoplasmic astrocyte. The Bergmann fibers were present at all stages examined, and their constant apposition to granule cells suggests a role in the lartter's migration. Numerous electronluscent beady enlargements are seen along the fiber except at sites were the surface is in contact with migrating cells; probably these enlargements change position as the granule cells pass along the Bergmann fiber. Lamellate expansions also project from the main shaft of the glial fiber and envelop the synaptic sites on spines of Purkinje cell dendrites. These expansions seem more durable, and the young neuron appears to avoid collision with them by sprialling around the glial shaft during its descent to the granular layer. The neuron-glia relationship apparently provides the necessary conditions for the migration of the young granule cell. Especially at late developmental stages when the molecular layer is more than 250 μ wide and is densely packed with highly oriented cell processes that have already established synaptic connections.

Approaches to Sudden Death from Coronary Heart Disease

Abstract: Sudden cardiac death (SCD) continues unabated. Coronary care units, while effective in lowering hospital mortality, cannot significantly reduce SCD which occurs primarily outside the hospital and accounts for the majority of deaths from coronary heart disease (CHD). In view of the frequent precipitous nature of SCD, only a program which identifies and protects the victim prior to the event can hope to be successful in preventing the majority of SCD. Since it is likely that SCD is due to an arrhythmia, drug prophylaxis might prove effective. In view of the toxicity of currently available agents, it is mandatory to preselect a population at highest risk before embarking on a drug trial. Ventricular premature beats (VPB) may identify subjects susceptible to SCD. Epidemiologic and physiologic information on VPB is reviewed, and proposals are made for studies designed to establish the usefulness of VPB as a risk factor for SCD.

On grain boundary sliding and diffusional creep

Abstract: The problem of sliding at a nonplanar grain boundary is considered in detail. The stress field, and sliding displacement and velocity can be calculated at a boundary with a shape which is periodic in the sliding direction (a wavy or stepped grain boundary): a) when deformation within the crystals which meet at the boundary is purely elastic, b) when diffusional flow of matter from point to point on the boundary is permitted. The results give solutions to the following problems. 1) How much sliding occurs in a polycrystal when neither diffusive flow nor dislocation motion is possible? 2) What is the sliding rate at a wavy or stepped grain boundary when diffusional flow of matter occurs? 3) What is the rate of diffusional creep in a polycrystal in which grain boundaries slide? 4) How is this creep rate affected by grain shape, and grain boundary migration? 5) How does an array of discrete particles influence the sliding rate at a grain boundary and the diffusional creep rate of a polycrystal? The results are compared with published solutions to some of these problems.

Reading and Auditory-Visual Equivalences

Abstract: A retarded boy, unable to read printed words orally or with comprehension, could match spoken words to pictures and could name pictures. After being taught to match spoken to printed words, he was ...

Systolic versus diastolic blood pressure and risk of coronary heart disease. The Framingham study.

Abstract: A comparison of the contribution of systolic versus diastolic blood pressure to risk of coronary heart disease and the role of mean arterial pulse pressure and systolic lability have been examined prospectively in 5,127 men and women during 14 years of biennial follow-up studies. Similar gradients of risk of subsequent coronary heart disease were observed whether persons were classified by their systolic or diastolic pressure, and no “safe” or critical level could be identified. Assessment of the net effect of each, employing discriminant analysis, indicated a stronger association of systolic than diastolic pressure with risk of coronary heart disease. Neither the systolic and diastolic pressure measurements in combination nor the pulse pressure and the mean arterial pressure measurements alone discriminated better than the systolic measurement alone. Systolic lability did not predict incidence of coronary heart disease independently of the associated level of blood pressure. There was a trend of declining relative importance of diastolic and a corresponding increase in the importance of systolic pressure with advancing age. Only in those under 45 was diastolic pressure predominant. The level of casually obtained blood pressure was a good predictor of coronary heart disease. The current practice of assessing the importance of blood pressure at all ages largely on the basis of diastolic pressure and the commonly held view concerning the innocuous nature of an elevated level of systolic pressure in the elderly requires reevaluation.

Menstrual synchrony and suppression

Abstract: Synchrony and suppression among a group of women living together in a college dormitory suggest that social interaction can have a strong effect on the menstrual cycle.

Amino-acid Sequence of Substance P

Abstract: IN 1931 von Euler and Gaddum1, studying the tissue distribution of acetylcholine, found that brain and intestine contained a substance that stimulated contraction of the isolated rabbit jejunum, and caused transient hypotension when injected intravenously into anaesthetized rabbits. These effects could not be ascribed to acetylcholine, for they were not prevented by the previous administration of atropine. The initial studies were made on crude acid alcohol extracts of equine brain and intestine, dried in powder form. The active principle in the preparation was later referred to as substance P (P for powder), and this non-committal term subsequently achieved widespread acceptance in the literature, in the absence of any clearly definable biological role for the compound (or compounds) involved.

The cytomegaloviruses: ubiquitous agents with protean clinical manifestations. II.

Abstract: Epidemiologic Aspects Distribution of CMV Surveys of unselected newborn infants in four cities in the United States and England indicate that some 1 per cent enter the world with an active infectio...

Reduction of residual ridges: a major oral disease entity.

Abstract: 1.Reduction of residual ridges (RRR) needs to be recognized for what it is: a major unsolved oral disease which causes physical, psychologic, and economic problems for millions of people all over the world. 2.RRR is a chronic, progressive, irreversible, and disabling disease, probably of multifactorial origin. At the present time, the relative importance of various cofactors is not known. 3.Much is known about the pathology and the pathophysiology of this oral disease, but we need to know much more about its pathogenesis, epidemiology, and etiology. 4.The ultimate goal of research of RRR is to find better methods of prevention or control of the disease. 5.Over 25 million Americans are estimated to be totally edentulous. The need for the delivery of more prosthodontic care in this country alone is staggering. 6.More research in RRR with new methods and new thinking are badly needed in order to provide the best possible oral health care for millions of edentulous patients.

Transitivity in Structural Models of Small Groups

Abstract: Our purpose here is to show how various deterministic models for the structure of interpersonal relations in small groups may all be viewed as special cases of a single model: namely, a transitive graph (t-graph). This exercise serves three purposes. First, the unified approach renders much of the mathematical discussion surrounding these various models quite transparent. Many of the arguments boil down to nothing more than defining certain equivalence relations and looking at the resulting equivalence classes. Second, our focus on the general model may stimulate the search for other useful specializations besides those indicated here. We discuss two ways of specializing the model-restrictions on edges and

Structural model for amorphous silicon and germanium

Abstract: A model for amorphous germanium and silicon has been constructed using the random network concept. Each atom has a first coordination number of four, and only a small variation in the nearest neighbor distance is allowed. Non-crystallinity is due to variations in the tetrahedral bond angle and rotations about bonds. No difficulty was encountered in continuing to make the model larger and no difference in structure between the central and outer regions could be observed. The radial distribution function and the density of the model agree well with recent measurements.

Alterations of macrophage functions by mediators from lymphocytes

Abstract: Sensitized lymphocytes were incubated in vitro with the specific antigen Supernatants from these cultures were chromatographed on Sephadex G-100 columns. Supernatant fractions containing MIF, chemotactic factor, and lymphotoxin, but free of antigen and antibody, were incubated with normal peritoneal exudate macrophages. Macrophage adherence, phagocytosis, spreading, motility, and direct hexose monophosphate oxidation were enhanced, while protein synthesis was unaffected. Thus, antigen-stimulated lymphocytes secrete a factor or factors which enhance certain macrophage functions. Implications for models of cellular immunity and cellular hypersensitivity are discussed.

The hemodynamic response to pulmonary embolism in patients without prior cardiopulmonary disease

Abstract: The hemodynamic status of 20 patients free of prior cardiopulmonary disease was related to the degree of pulmonary embolic obstruction estimated by selective pulmonary angiography. Angiographic estimation of obstruction ranged from 13 to 68 percent. Systemic arterial hypoxemia occurred in virtually all patients (95 percent) including those with only 13 percent obstruction, thus suggesting that angiographically detectable emboli virtually do not occur without producing systemic hypoxemia. Mean pulmonary arterial pressure was increased in 14 patients (70 percent) and was consistently increased when obstruction exceeded 30 percent. Elevation of the level of mean right atrial pressure was found in 10 patients (50 percent) and was usually associated with obstruction in excess of 35 percent and mean pulmonary arterial pressure in excess of 30 mm Hg. Good correlation was observed between mean pulmonary arterial pressure and angiographic estimation of obstruction (P

Immunological release of histamine and slow reacting substance of anaphylaxis from human lung.

Abstract: The immunologic release of histamine and slow reacting substance of anaphylaxis (SRS-A) from human lung tissue can be enhanced by stimulation with either alpha adrenergic agents (phenylephrine or norepinephrine in the presence of propranolol) or cholinergic agents (acetylcholine or Carbachol). The finding that atropine prevents cholinergic but not comparable alpha adrenergic enhancement is consistent with the view that cholinergic and alpha adrenergic agonists interact with separate receptor sites on the target cells involved in the immunologic release of chemical mediators. The consistent qualitative relationship between the antigen-induced release of mediators and the level of cyclic adenosine monophosphate (cyclic AMP) as measured by the isolation of 14C-labeled cyclic AMP after incorporation of adenine-14C into the tissues or by the cyclic AMP binding protein assay suggests that changes in the level of this cyclic nucleotide mediate adrenergic modulation of the release of histamine and SRS-A. The addition of 8-bromo-cyclic guanosine monophosphate (cyclic GMP) produces an enhancement of the immunologic release of mediators while dibutyryl cyclic AMP is inhibitory. As cholinergic-induced enhancement was not associated with a measurable change in the levels of cyclic AMP, the possibility is suggested that cyclic GMP may be the intracellular mediator of cholinergic-induced enhancement of the immunologic release of histamine and SRS-A.

Clinical, cephalometric, and densitometric study of reduction of residual ridges.

Abstract: 1.A clinical, cephalometric, and densitometric study of the reduction of residual ridges (RRR) was carried out on 76 edentulous clinic patients (44 women and 32 men) with a mean age 65.2 years (range of 38 to 87 years). 2.In this group of patients with varying periods of time since extraction, a high proportion of maxillary ridges were high and well rounded (Order III), including 50 per cent of those 20 years or more after extraction. In contrast, only 24 per cent of the mandibular ridges were classified as high and well rounded, and of these, 80 per cent were 2 years or less postextraction with 54 per cent classified as knife-edge (Order IV). 3.The rate of total anterior RRR varied between individuals, being immeasurable in 23 per cent and 1 mm. or more per year in 20 per cent. The highest rate in one subject studied over 3 years was 2.2 mm. per year. The average rate was 0.5 mm. per year. 4.The rate of RRR varied between the upper and lower jaws averaging 0.1 mm. per year for the maxillae and 0.4 mm. per year for the mandible. Thus, the average rate for the lower jaw was four times that of the upper. Yet, 9 per cent of the subjects had a higher rate on the maxillae than on the mandible, while the rate was the same in 26 per cent. 5.There was a low correlation between the rate of RRR and several possible cofactors, including sex, age, and bone density. 6.An average rate of anterior vertical RRR of 0.5 mm. per year could represent an average loss of 5 mm. in anterior ridge height (considerably more in some patients) in 10 years, resulting in significant loss of vertical dimension, esthetics, and comfort. Such remarkable changes in millions of edentulous people represent a staggering need for prosthodontic care. 7.New methods of prevention and treatment of this disabling disease must be found.