Showing papers by "University of Pennsylvania published in 1976"

The clonal evolution of tumor cell populations

Abstract: It is proposed that most neoplasms arise from a single cell of origin, and tumor progression results from acquired genetic variability within the original clone allowing sequential selection of more aggressive sublines. Tumor cell populations are apparently more genetically unstable than normal cells, perhaps from activation of specific gene loci in the neoplasm, continued presence of carcinogen, or even nutritional deficiencies within the tumor. The acquired genetic insta0ility and associated selection process, most readily recognized cytogenetically, results in advanced human malignancies being highly individual karyotypically and biologically. Hence, each patient's cancer may require individual specific therapy, and even this may be thwarted by emergence of a genetically variant subline resistant to the treatment. More research should be directed toward understanding and controlling the evolutionary process in tumors before it reaches the late stage usually seen in clinical cancer.

Social Structure from Multiple Networks. I. Blockmodels of Roles and Positions

Abstract: Networks of several distinct types of social tie are aggregated by a dual model that partitions a population while simultaneously identifying patterns of relations. Concepts and algorithms are demonstrated in five case studies involving up to 100 persons and up to eight types of tie, over as many as 15 time periods. In each case the model identifies a concrete social structure. Role and position concepts are then identified and interpreted in terms of these new models of concrete social structure. Part II, to be published in the May issue of this Journal (Boorman and White 1976), will show how the operational meaning of role structures in small populations can be generated from the sociometric blockmodels of Part I.

Antibody to acetylcholine receptor in myasthenia gravis Prevalence, clinical correlates, and diagnostic value

Abstract: Elevated amounts of antibodies specific for acetylcholine receptors were detected in 87 percent of sera from 71 patients with myasthenia gravis but not in 175 sera from individuals without myasthenia gravis, including those with other neurologic or autoimmune diseases. Antireceptor antibodies were not directed at the acetylcholine binding site of the receptor. Presence or titer of antibody did not appear to correlate with age, sex, steroid therapy, or duration of symptoms. Myasthenia gravis patients with only ocular symptoms had lower antibody titers, while the majority of titers in myasthenia gravis patients with thymoma exceeded the median titer of the myasthenia gravis group as a whole. Assay of antireceptor antibody should prove a useful test in the diagnosis of myasthenia gravis.

Options and Efficiency

Abstract: This paper argues that in an uncertain world options written on existing assets can improve efficiency by permitting an expansion of the contingencies that are covered by the market. The two major results obtained are, first, that complex contracts can be "built up" as portfolios of simple options and, second, that there exists a single portfolio of the assets, the efficient fund, on which all options can be written with no loss of efficiency. An option contract is any security whose returns are dependent on the returns of some other underlying security (or securities). Warrants, puts, and calls are familiar financial examples of options written on stocks, but preferred stock and subordinated debentures and even such diverse contracts as life insurance policies could also be viewed as options. The serious study of options in the financial literature began with the long-neglected thesis by Bachelier and was revived in the 1960's by a number of authors who focused in on the pricing problem, i.e., the problem of determining the equilibrium relationship between the value of an option and the value of the stock it is written on.1 The intention of this paper is to consider the related problem of the efficiency aspects of option contracts. Arrow's 2 introduction of the state-space approach to uncertainty in economics has brought the recognition that an inadequate number of markets in contingent claims would be a source of inefficiency. In the state-space approach the random events that might occur are subsets of elementary points or "states" in a (probability) space, and the possibility of inefficiency arises whenever the feasible set of pure contingent claims, claims to wealth if a single state occurs and nothing otherwise, fails to span all the state

On the Nature, Formation, and Maintenance of Relations Among Organizations

Abstract: A relationship between two or more organizations is a social action system because it exhibits the basic properties of any organized form of collective behavior. Dimensions commonly used to examine social structure and process are appropriate for defining and evaluating the characteristics of inter-organizational relationships. A theory is developed on how and why relationships between organizations voluntarily emerge and are maintained.

Quasiparticle and phonon lifetimes in superconductors

Abstract: Low-energy quasiparticle scattering, recombination, and branch-mixing lifetimes and phonon pair-breaking and scattering lifetimes are calculated for superconductors. The quasiparticle calculations relate these lifetimes to the low-frequency behavior of ${\ensuremath{\alpha}}^{2}(\ensuremath{\Omega})F(\ensuremath{\Omega})$. Results are obtained using the low-frequency approximate form ${\ensuremath{\alpha}}^{2}(\ensuremath{\Omega})F(\ensuremath{\Omega})=b{\ensuremath{\Omega}}^{2}$, with $b$ determined from electron tunneling measurements. For the strong-coupling superconductors Pb and Hg, the full tunneling form for ${\ensuremath{\alpha}}^{2}(\ensuremath{\Omega})F(\ensuremath{\Omega})$ is used. The phonon lifetimes are shown to depend on ${\ensuremath{\alpha}}^{2}(\ensuremath{\Omega})$. Results are compared with experiment.

Neuroendocrine Regulation in Depression: I. Limbic System-Adrenocortical Dysfunction

Abstract: • The regulation of hypothalamopituitary-adrenal (HPA) function in depressed patients was studied by a midnight dexamethasone suppression test. By using an observation period of 24 hours postadministration of dexamethasone, a graded series of abnormal test responses was identified. Depressed patients show abnormal early escape from suppression rather than absolute resistance to HPA suppression by dexamethasone. With increasing severity of depression, this escape occurs progressively more early on the day after administration of dexamethasone. These abnormalities were strongly related to the presence of HPA hyperactivity before dexamethasone was given. The essential disturbance of neuroendocrine regulation in depression is a failure of the normal brain inhibitory influence on the HPA system. This disinhibition of HPA activity suggests that there is an abnormal limbic system drive on the HPA axis in primary depressive illness.

Structure of the microbial flora associated with periodontal health and disease in man. A light and electron microscopic study.

Abstract: Teeth slated for extraction were evaluated with respect to their periodontal status and classified accordingly into five categories; namely normal, gingivitis, periodontitis, periodontosis and postperiodontosis. After processing, one approximal surface of each tooth was sampled at various levels in an apico-occlusal direction for light and electron microscopic study of the associated bacterial flora. In normal samples, the flora consisted of a relatively thin, adherent bacterial layer confined to the enamel surface. The cells were predominantly coccoid in shape with cell wall features compatible with those of Gram-positive organisms. Isolated filamentous or branching forms and some Gram-negative bacteria were noted on the surface of the more apical portion of the bacterial layer. No flagellated cells or spirochetes were present. Gingivitis samples yielded a relatively more voluminous and complex supragingival flora with relatively more filamentous bacteria and more cells with a Gram-negative cell wall ultrastructure. These samples also contained corncob formations on the surface of supragingival deposits, and flagellated cells with spirochetes within the predominantly Gram-negative flora of the sulcus bottom. Supragingival bacterial deposits of periodontitis samples were similar to those observed in gingivitis. The subgingival flora consisted of relatively fewer cells adherent to the root surface with a concomitant increase in the population of Gram-negative and flagellated cells, as well as spirochetes. The tissue side of the subgingival flora generally exhibited a distinctive concentration of "test-tube brush" formations, spirochetes of predominantly medium size, and assorted cell types peculiar to this region. A transitional flora generally separated the supra- from the subgingival microbial population. Periodontosis samples had a relatively sparse, predominantly Gram-negative flora. A unique electron-dense, lobulated cuticular deposit covered the majority of the samples studied. Postperiodontosis samples were much more similar in their microbial flora to the periodontitis group. The results suggest that (1) a certain microbial flora may be compatible with a state of periodontal health; (2) a different flora is associated with varying degrees of periodontal disease; (3) the structure and composition of the supragingival flora differs markedly from that of the subgingival flora; (4) with the exception of periodontis, the alterations of the microbial flora as periodontal disease increases inseverity parallel the changes described previously in the microbial population collected on artificial crowns during experimentally induced gingivitis. The use of the expressions "microbial flora" or "microbial population" is considered preferable to the terms "plaque", "materia alba", or "debris" in reference to the microbiota of the gingival sulcus region.

The Selection of Foods by Rats, Humans, and Other Animals

Abstract: Publisher Summary This chapter discusses the selection of food by rats, humans, and other animals, and focuses on the complex problems, especially in food recognition and choice, in the omnivores or generalists. Food selection implies food ingestion. Food ingestion implies the presence of food. Therefore, background for the study of food selection includes the food search process: search images and search mechanisms for finding appropriate food stimuli in the environment. Honey bees provide fine examples of a highly developed food search system. Food selection also implies the ability to obtain or capture food, and to assimilate it, for which many often exotic mechanisms have been evolved. Given the presence of potential food, ingestion then usually depends on an internal state or detector indicating a “need” for the particular food or class of foods, and recognition of the potential food as food. Omnivores, such as rats and humans, faced with an enormous number of potential foods, must choose wisely. They are always in danger of eating something harmful or eating too much of a good thing. Although there are some helpful internal mechanisms, such as poison detoxification, nutrient biosynthesis, and nutrient storage, the major share of the burden for maintaining nutritional balance must out of necessity come from incorporation of appropriate nutrients in the environment and, hence, behavior. The most striking parallel between human and rat feeding is in the neophobia seen in both. The chapter discusses the multiple determinants of food selection in man that are divided into biological factors and effects of individual experience, on one hand, and cultural influences, on the other.

The effects of glucose and insulin on renal electrolyte transport.

Abstract: The effects of hyperglycemia and hyperinsulinemia on renal handling of sodium, calcium, and phosphate were studied in dogs employing the recollection micropuncture technique. Subthreshold sustained hyperglycemia resulted in an isonatric inhibition of proximal tubular sodium, fluid, calcium, and phosphate reabsorption by 8-14%. Fractional excretion of sodium and phosphate, however, fell (P is less than 0.01) indicating that the increased delivery of these ions was reabsorbed in portions of the nephron distal to the site of puncture and in addition net sodium and phosphate transport was enhanced resulting in a significant antinatriuresis and antiphosphaturia. The creation of a steady state plateau of hyperinsulinemia while maintaining the blood glucose concentration of euglycemic levels mimicked the effects of hyperglycemia on proximal tubular transport and fractional excretion of sodium and calcium. Tubular fluid to plasma insulin ratio fell, similar to the hyperglycemic studies. These results suggest that the effects of hyperglycemia on renal handling of sodium and calcium may be mediated through changes in plasma insulin concentration. In contrast to hyperglycemia, however, hyperinsulinemia cuased a significant fall in tubular fluid to plasma phosphate ratio with enhanced proximal tubular phosphate reabsorption (P is less than 0.02). This occurred concomitantly with a significant inhibition of proximal tubular sodium transport. These data indicate that insulin has a direct effect on proximal tubular phosphate reabsorption, and this effect of insulin is masked by the presence of increased amounts of unreabsorbed glucose in the tubule that ensues when hyperinsulinemia occurs secondary to hyperglycemia. Fractional excretion of phosphate fell significantly during insulin infusion but unlike the hyperglycemic studies, the fall in phosphate excretion could be entirely accounted for by enhanced proximal reabsorption.

Social Change and Transitions to Adulthood in Historical Perspective

Abstract: *John Modell is Associate Professor of History, University of Minnesota, and Research Associate, Philadelphia Social History Project. Frank F. Furstenberg, Jr. is Associate Professor of Sociology, University of Pennsylvania. Theodore Hershberg is Associate Professor of History, University of Pennsylvania, and Director, Philadelphia Social History Project. An earlier version of this paper was presented at the annual meetings of the American Sociological Association in San Francisco, August, 1975. Rules can be found in every society governing the passage to adulthood. In some

Ultraviolet Photoionization Cross Sections for N 2 and CO

Abstract: I have calculated ultraviolet photoionization cross sections for ${\mathrm{N}}_{2}$ and CO in the gas phase and the differential cross sections for oriented molecules. The gas-phase results agree well with recent data and display shape resonances, predicted by Dehmer and Dill, about 1 Ry above threshold for certain levels. For oriented molecules I find distinctive angular distributions which could be used to identify levels or determine the bond geometry of molecules adsorbed at surfaces.

Why do women live longer than men

Abstract: In the contemporary United States, males have 60 percent higher mortality than females. In Part I, published in the previous issue, we showed that 40 percent of this sex differential in mortality is due to a twofold elevation of arteriosclerotic heart disease among men. Major causes of higher rates of arteriosclerotic heart disease in men include greater cigarette smoking among men; probably a greater prevalence of the competitive, aggressive Coronary Prone Behavior Pattern among men; and possibly a protective role of female hormones. In addition, men have higher death rates for lung cancer and emphysema, primarily because more men smoke cigarettes. In Part II we analyze the other major causes of men's higher death rates: accidents, suicide, and cirrhosis of the liver. Each of these is related to behaviors which are encouraged or accepted more in men than in women in our society--for example, using guns, being adventurous and acting unafraid, working at hazardous jobs and drinking alcohol. We conclude with suggestions for reducing male mortality; for example, by changing the social conditions which foster in men the behaviors that elevate their mortality.

Variations in writing posture and cerebral organization

Abstract: Two tachistoscopic tests of cerebral lateralization were administered to 73 subjects classified by handedness, sex, and hand orientation in writing. The results indicated that the direction of cerebral lateralization could be indexed from a subject's handedness and hand posture during writing. In subjects with a normal writing posture, the linguistically specialized hemisphere was contralateral to the dominant hand, and the visuospatially specialized hemisphere was ipsilateral; the reverse was true in subjects with an "inverted" hand position during writing. Females and subjects having an inverted hand posture manifested smaller degrees of lateral differentiation than males and subjects with a typical hand posture.

The hematopoietic microenvironment of the bone marrow: An ultrastructural study of the stroma in rats

Abstract: The bone marrow contains branching vascular sinuses lying in a fibroblastic stroma which supports hematopoiesis. This paper describes the stroma and vascular sinuses by scanning and transmission electron microscopy and in freeze-fracture etch replicas in normal fat femoral marrow and in rats made eosinophilic by larvae of trichinella spiralis. The stroma consists primarily of reticular cells which ensheath sinuses as adventitial cells and branch into the surrounding hematopoietic space. They form a spongework on which hematopoietic cells are arranged. Erythroblasts, clustered into islets, and megakaryocytes lie just outside sinuses. Granulocytes, until the metamyelocyte stage, lie in the midst of the hematopoietic cords. Lymphocytes, monocytes and likely stem cells, are clustered about arterial vessels. Macrophages occur throughout the marrow. Fat cells occur adventitial to vascular sinuses and appear to be reticular cells which accumulate fat. Processes of reticular cells closely envelope hematopoietic cells or protrude into them. Reticular cells contain rough ER and are likely fibroblastic. The argyrophilic reticular fibers of the marrow are, however, slender and scanty. Reticular cells are rich in filaments and they may contain many microtubules. They are not phagocytic and possess few lysosomes. The reticular cell cover of a vascular sinus is lifted away as maturing hematopoietic cells approach the sinus, preparatory to crossing the endothelium and entering the circulation. Maturing granulocytes often show microvilli on reaching the basal endothelial surface. The level of eosinophils in the marrow may increase from approximately four to more than 20% after injection of trichinella larvae. Close distinctive association of reticular cells and eosinophils are marked. Reticular cells provide a physical spongwork on which hematopoietic cells are supported. But I postulate that they also trap and induce differentiation of hematopoietic stem cells, and sort the differentiating hematopoietic cells into characteristic locations in their spongework.

Two-photon absorption by rotating diatomic molecules

Abstract: Explicit forms for the two-photon absorption cross section in linearly and circularly polarized light for rotating diatomic molecules have been developed. The ratio (σλλ/σ cc ) of the cross sections for individual rotational transitions is precisely two-thirds for all branches of ΔΩ = 0, ±1, ±2 transitions except for the unique case—the Q branch of a ΔΩ=0 transition. In the latter case the ratio becomes J-dependent and may range from infinity to 4/1 (for high J) for different relative contributions to the absorption cross section of intermediate states having either the same or different electronic symmetry. These contributions are thus experimentally accessible in this favourable situation.

A dual algorithm for the one-machine scheduling problem

Abstract: A branch and bound algorithm is presented for the problem of schedulingn jobs on a single machine to minimize tardiness. The algorithm uses a dual problem to obtain a good feasible solution and an extremely sharp lower bound on the optimal objective value. To derive the dual problem we regard the single machine as imposing a constraint for each time period. A dual variable is associated with each of these constraints and used to form a Lagrangian problem in which the dualized constraints appear in the objective function. A lower bound is obtained by solving the Lagrangian problem with fixed multiplier values. The major theoretical result of the paper is an algorithm which solves the Lagrangian problem in a number of steps proportional to the product ofn 2 and the average job processing time. The search for multiplier values which maximize the lower bound leads to the formulation and optimization of the dual problem. The bounds obtained are so sharp that very little enumeration or computer time is required to solve even large problems. Computational experience with 20-, 30-, and 50-job problems is presented.

Langerhans cells form a reticuloepithelial trap for external contact antigens

Abstract: THE outermost covering of the body, the epidermis, is a thin epithelial sheath comprising three distinct cell types, keratinocytes, melanocytes and Langerhans cells. The physicochemical and photo-protective role of the first two is well known, but the function of the third is still unknown, over a hundred years since its discovery1. The Langerhans cell was reported earlier as having a sensory role, or as being an effete form of the dendritic malanocyte below it2, but it occurs in the dermis3 and is mesenchymal, rather than neuroectodermal, in origin. Its fine structure reveals no melanin, but distinctive racquet-shaped granules. It has also been proposed that it is a macrophage4 or that it may be involved in keratinisation, but recent evidence has suggested an immune function for the Langerhans cell in the development of contact dermatitis5,6. To investigate this possibility, we have exposed separated epidermal sheets to metals, aldehydes and amines known to act as contact antigens, and have observed their distribution histologically. We report here the selective uptake of antigens causing allergic contact dermatitis by Langerhans cells of the epidermis in guinea pigs and man.

Speech events and natural speech: some implications for sociolinguistic methodology,

Abstract: Samples of speech suitable for sociolinguistic analysis may be sought in several ways. Interviews (either formal or informal), and tape-recorded group sessions, are the methods most used currently. In research on a specific variable, the historical present tense (HP), none of these methods proved neutral or adequate. Although the historical present tense is very widely used in conversational narratives, its occurrence within interviews is so infrequent as to be striking. An explanation was found in the way in which the interview has a specific known place as a speech event in the culture of those whose speech was being studied. The so-called spontaneous interview does not have such a place, and for that very reason is even less satisfactory a source of data. The notion of natural speech is taken as properly equivalent to that of appropriate speech; as not equivalent to unselfconscious speech; and as observable easily, and often best, by simple techniques of participation. (Sociolinguistic methodology; speech events, interviews, observation, natural speech; United States English).

Production of amorphous alloy ribbons and effects of apparatus parameters on ribbon dimensions

Abstract: An apparatus for the production of amorphous alloy ribbon is described. The alloy is induction-melted in a small quartz crucible and ejected by argon gas pressure through a small orifice in the bottom of the crucible. The liquid jet impinges at a small angle with respect to a radius of a copper disk rotating at several thousand rev/min, flattens while rapidly cooling and solidifying, and leaves the circumferential surface of the disk as a result of centrifugal force. The resulting ribbon geometry for an alloy of Fe 40 Ni 40 B 20 has been studied as a function of orifice sizes between 340 and 480 μm in diameter, of disk speeds between 5 and 10 \times 10^{3} rev/min (20 and 40 m/sec), and of ejection pressures between 4 and 10 psig (28 and 70 kPa). The cross-sectional area of the ribbon can be predicted quite accurately from the disk speed, the orifice diameter, and the velocity of the liquid jet as given by the Bernoulli equation. Experimental data are in the form of ribbon thicknesses, ranging between 10 and 40 μm, and mass/ length, ranging between 0.05 and 0.24 mg/mm. None of the ribbons produced showed any signs of crystallinity, as determined by X-ray diffraction.