Showing papers by "University of Pennsylvania published in 1969"

Formation of arrowhead complexes with heavy meromyosin in a variety of cell types.

Abstract: Heavy meromyosin (HMM) forms characteristic arrowhead complexes with actin filaments in situ. These complexes are readily visualized in sectioned muscle. Following HMM treatment similar complexes appear in sectioned fibroblasts, chondrogenic cells, nerve cells, and several types of epithelial cells. Thin filaments freshly isolated from chondrogenic cells also bind HMM and form arrowhead structures in negatively stained preparations. HMM-filament complexes are prominent in the cortex of a variety of normal metaphase and Colcemid-arrested metaphase cells. There is no detectable binding of HMM with other cellular components such as microtubules, 100-A filaments, tonofilaments, membranes, nuclei, or collagen fibrils. The significance of HMM-filament binding is discussed in view of the finding that arrowhead complexes form in types of cells not usually thought to contain actin filaments.

Auto-maintenance in the pigeon: sustained pecking despite contingent non-reinforcement.

Abstract: If a response key is regularly illuminated for several seconds before food is presented, pigeons will peck it after a moderate number of pairings; this “auto-shaping” procedure of Brown and Jenkins (1968) was explored further in the present series of four experiments. The first showed that pecking was maintained even when pecks turned off the key and prevented reinforcement (auto-maintenance); the second controlled for possible effects of generalization and stimulus change. Two other experiments explored procedures that manipulated the tendency to peck the negatively correlated key by introducing alternative response keys which had no scheduled consequences. The results indicate that pecking can be established and maintained by certain stimulus-reinforcer relationships, independent of explicit or adventitious contingencies between response and reinforcer.

A concept of corporate planning

Abstract: In this article, Professor Ackoff develops a new concept of planning, Adaptive Planning—in a systematic way and attempts to exploit the management and behavioural sciences to the fullest. He discusses the nature of planning, the parts of the planning system, and the different philosophies of planning—which he calls satisficing, optimizing, and adaptivizing. He concludes that “at the present time satisficing planning is the only one of the three approaches to which we can normally adhere completely.”

Exchange Interaction in Alloys with Cerium Impurities

Abstract: Starting with the Anderson model for the $4{f}^{1}$ configuration of cerium, the transformation of Schrieffer and Wolff is performed, taking into account combined spin and orbit exchange scattering. The resultant interaction Hamiltonian differs qualitatively from the conventional $s\ensuremath{-}f$ exchange interaction. The Kondo effect, the spin-disorder resistivity, the Ruderman-Kittel interaction, and the depression of the super-conducting transition temperature with impurity concentration are worked out for alloys containing cerium impurities on the basis of this new interaction.

Simultaneously recorded trains of action potentials: analysis and functional interpretation.

Abstract: A new kind of statistical display, the joint peri-stimulus-time scatter diagram, facilitates the analysis and interpretation of two or more simultaneously recorded trains of action potentials. The display is a generalization of the cross correlation and the peri-stimulus-time histogram, and it reflects specific underlying neuronal interactions. The technique yields quantitative measures of interaction in terms of effectiveness of synaptic connections.

The histogenesis of rat intercostal muscle.

Abstract: Intercostal muscle from fetal and newborn rats was examined with the electron microscope. At 16 days' gestation, the developing muscle was composed of primary generations of myotubes, many of which were clustered together in groups. Within these groups, the membranes of neighboring myotubes were interconnected by specialized junctions, including tight junctions. Morphologically undifferentiated cells surrounded the muscle groups, frequently extended pseudopodia along the interspace between adjacent myotubes, and appeared to separate neighboring myotubes from one another. At 18 and 20 days' gestation, the muscle was also composed of groups of cells but the structure of the groups differed from that of the groups observed at 16 days. Single, well differentiated myotubes containing much central glycogen and peripheral myofibrils dominated each group. These large cells were interpreted as primary myotubes. Small, less differentiated muscle cells and undifferentiated cells clustered around their walls. Each cluster was ensheated by a basal lamina. The small cells were interpreted as primordia of new generations of muscle cells which differentiated by appositional growth along the walls of the large primary myotubes. All generations of rat intercostal muscle cells matured to myofibers between 20 days' gestation and birth. Coincidentally, large and small myofibers diverged from each other, leading to disintegration of the groups of muscle cells. Undifferentiated cells frequently occurred in the interspaces between neighboring muscle cells at the time of separation. Myofibers arising at different stages of muscle histogenesis intermingled in a checkerboard fashion as a result of this asynchronous mode of development. The possibility of fusion between neighboring muscle cells in this developing system is discussed.

Vitellogenic Blood Protein Synthesis by Insect Fat Body

Abstract: The female fat body of a moth and a roach incorporated labeled amino acids in vitro into substances precipitable by antibodies formed in response to the sex-limited vitellogenic blood proteins of these species. The fat body of males failed to do so, as did that of females before the appearance of these proteins in the blood.

Mitosis and the processes of differentiation of myogenic cells in vitro

Abstract: The relation between the mitotic cycle and myoblast fusion has been studied in chick skeletal muscle in vitro The duration of the cell cycle phases was the same in both early and late cultures By tracing a cohort of pulse-labeled cells, it was found that myoblast fusion does not occur in S, G2, or M Cell surface alterations required for fusion are dependent upon the position of the cell in the division cycle In early cultures, fusion takes place only after a minimum delay of 5 hr from the time the cell has entered G1 The mitosis preceding fusion may condition the cell for the abrupt shift in synthetic activity that occurs in the subsequent G1 In older cultures fusion of labeled cells is diminished Two factors account for the cessation of fusion in older cultures First, the number of myogenic stem cells declines, but these cells do not disappear as the cultures mature Their persistence was demonstrated by labeling dividing mononucleated cells in older cultures and challenging them with nascent myotubes Some of these labeled cells were incorporated into the forming myotubes Second, a block to fusion develops during myotube maturation Well developed myotubes challenged with labeled competent myogenic cells failed to incorporate the labeled nuclei

The fine structure of motor endplate morphogenesis.

Abstract: The fine structure of the developing neuromuscular junction of rat intercostal muscle has been studied from 16 days in utero to 10 days postpartum. At 16 days, neuromuscular relations consist of close membrane apposition between clusters of axons and groups of myotubes. Focal electron-opaque membrane specializations more intimately connect axon and myotube membranes to each other. What relation these focal contacts bear to future motor endplates is undetermined. The presence of a group of axons lying within a depression in a myotube wall and local thickening of myotube membranes with some overlying basal lamina indicates primitive motor endplate differentiation. At 18 days, large myotubes surrounded by new generations of small muscle cells occur in groups. Clusters of terminal axon sprouts mutually innervate large myotubes and adjacent small muscle cells within the groups. Nerve is separated from muscle plasma membranes by synaptic gaps partially filled by basal lamina. The plasma membranes of large myotubes, where innervated, simulate postsynaptic membranes. At birth, intercostal muscle is composed of separate myofibers. Soleplate nuclei arise coincident with the peripheral migration of myofiber nuclei. A possible source of soleplate nuclei from lateral fusion of small cells' neighboring areas of innervation is suspected but not proven. Adjacent large and small myofibers are mutually innervated by terminal axon networks contained within single Schwann cells. Primary and secondary synaptic clefts are rudimentary. By 10 days, some differentiating motor endplates simulate endplates of mature muscle. Processes of Schwann cells cover primary synaptic clefts. Axon sprouts lie within the primary clefts and are separated from each other. Specific neural control over individual myofibers may occur after neural processes are segregated in this manner.

Conditional Demand Functions and Consumption Theory

Abstract: Introduction, 60. — I. Conditional demand functions, 61. — II. Conditional demand functions and ordinary demand functions, 64. — III. A new decomposition of the cross price derivatives, 65. — IV. Consumer behavior under straight rationing, 70. — V. Hicksian aggregation, 74. — VI. The Le Chatelier Principle and beyond, 75.

Escherichia coli K-12 mutants resistant to nalidixic acid: genetic mapping and dominance studies.

Abstract: Escherichia coli K-12 strains tested so far (approximately 20) can be separated into three groups on the basis of their abilities to form colonies on nutrient agar supplemented with nalidixic acid (NAL): (i) Nals or wild type (no growth at 1 to 2 μg/ml); (ii) NalAr (growth at 40 μg/ml or higher); and (iii) NalBr (growth at 4 μg/ml, but no growth at 10 μg/ml). The NalAr group has a spectrum of sensitivity ranging from 60 to over 100 μg/ml. All Hfr strains of the NalAr and NalBr groups transfer NAL resistance to recipient cells at genetic loci which are at 42.5 ± 0.5 and 51 ± 1 min, respectively, on the Taylor-Trotter map. Some members of the NalAr group also have the genetic locus for NalBr. The nalAs allele is completely dominant to nalAr in a partial diploid configuration. In haploids, nalAr-nalBr is phenotypically NalAr; nalAr-nalBs is NalAr; and nalAs-nalBr is NalBr. The map location of nalA and the easy differentiation between NalAr and NalAs allow this marker to be used as a counterselector in bacterial conjugation experiments.

A Media Planning Calculus

Abstract: A convenient on-line computer system selects and schedules advertising media. The system consists of a market-response model, a heuristic search routine, and a conversational input-output program. The user supplies a list of media options, a budget, and various objective and subjective data about the media options and the desired audience. The system selects a set of options and schedules them over time, seeking to maximize total market response. The model of market response works as follows: The population is divided into market segments. People in each segment are characterized by their sales potential and media habits. Ads placed in the media options lead people to be exposed to the advertising. The pattern of exposures in each market segment is determined by media coverage and duplication data. People tend to forget exposures and so the retained exposure level decays in the absence of new advertising. The response of an individual, in terms of the fraction of sales potential realized by the advertiser, increases with exposure level but with diminishing returns. Total market response is a sum over people, market segments, and time periods. The calculation of response is based on analytic formulas that are computationally very efficient. A maximum-seeking, heuristic calculation starts with any schedule, adds options with a high increment of response per dollar and deletes options with a low increment per dollar until no more improvement can be found for the given budget. An on-line system, called mediac, permits the use of model and heuristic at a remote console of a time-shared computer. Communication with the computer is conversational and largely self-explanatory. The system is operational. Computing costs have been a fraction of a per cent of the cost of the media scheduled. Improvements over previous schedules, as calculated by the model from the user's input data, have run from 5 per cent to over 20 per cent.

Historical foundations of the common law

Abstract: PART I: INSTITUTIONAL BACKGROUND PART II: PROPERTY IN LAND PART III: OBLIGATIONS PART IV: CRIME

The loss of phenotypic traits by differentiated cells. VI. Behavior of the progeny of a single chondrocyte.

Abstract: A single, functional, mitotically quiescent chondrocyte may be induced to reenter the mitotic cyde, and produce a progeny of over 1011 cells. Sessile, adherent, polygonal cells deposit matrix, whereas amoeboid, dispersed, flattened fibroblastic cells do not. The prior synthetic history of a cell is of greater importance in determining whether the characteristic chondrogenic phenotype will be expressed, rather than growth in "permissive" or "nonpermissive" medium. Clonal conditions select for stem-like cells, some of whose progeny may become polygonal chondrocytes. The retention of the characteristic chondrogenic phenotype in vitro is favored by pruning the dedifferentiated chondrocytes which arise in these cultures. Dedifferentiated chondrocytes interfere with the deposition and synthesis of chondroitin sulfate by neighboring functional chondrocytes. Possible mechanisms are proposed to explain this type of cell-cell or cell exudate interference. If the progeny of a single, genetically programmed chondrocyte may or may not synthesize chondroitin sulfate, then extragenic sites in the cytoplasm or cell surface must influence the decision as to which cluster of "luxur" molecules the cell will synthesize.

Contribution to the Theory of Disordered Alloys

Abstract: A simple model of a disordered substitutional alloy, similar in some respects to transition-metal alloys, is studied in several approximations. A formalism is presented in which the Green's function for the alloy is represented in the form of an infinite perturbation series, the lowest term of which is the coherent-potential approximation introduced earlier. The average density of states for several model alloys is investigated, and it is found that corrections to the rigid-band model can be significant even in situations in which the constitutents are not very dissimilar. Study of certain terms in the perturbation series suggests that the coherent-potential approximation is adequate in many situations. The density of states localized about a particular type of atom is shown to bear little resemblance to the average density of states. It can be a strong function of the environment, but if an average environment is taken, the coherent-potential scheme gives good results. The variation of average and local state densities as a function of concentration is studied for a particular model.

Ternäre Erdalkali-und Seltene Erdmetall-Silicide und-Germanide mit ThCr 2 Si 2 -Struktur

Abstract: Es wurden 53 neue Verbindungen mit der ZusammensetzungRM 2 B 2 IV hergestellt, wobeiR ein Selten-Erdelement, Ca oder Sr bedeutet,M eines der Elemente: Cr, Fe, Co, Ni oder Cu ist undB IV entweder Si oder Ge bezeichnet. Alle Verbindungen kristallisieren im tetragonalen ThCr2Si2-(oder CeAl2Ga2-) Strukturtyp. Der letztere stellt eine geordnete ternare Variante des BaAl4-Typs dar, bei dem die zwei ungleichwertigen Al-Punktlagen mit verschiedenartigen Atomen besetzt sind.

The Chemical Energetics of Muscle Contraction. II. The Chemistry, Efficiency and Power of Maximally Working Sartorius Muscles

Abstract: Sartorius muscles from Rana pipiens were stretched and then stimulated electrically at 0°C whilst being allowed to shorten at constant predetermined velocities on a Levin-Wyman ergometer. The muscles developed tensions appropriate to their instantaneous lengths and velocities. A comparison with the unstimulated paired control muscle allowed measurements to be made of the changes in phosphate compounds during these maximally-working, constant-velocity contractions. In contractions lasting less than 1.5 s, no significant dif­ferences were found in the usage of adenosine triphosphate or production of inorganic phosphate, for the performance of a constant amount of work, in normal aerobic muscles, anaerobic muscles pretreated with iodoacetate to inhibit lactate production, or muscles pre­treated with 2, 4-dinitrofluorobenzene so that adenosine triphosphate was the only energy source. In slow contractions lasting longer than 1.5 s allowance had to be made for myokinase and other enzymic reactions. The amount of external work done by the muscles, as a result of the hydrolysis of each mole of adenosine triphosphate, was found to be very dependent on velocity, being low at low and high speeds of shortening with a maximum below 1 muscle length/second. The free energy available per mole of adenosine triphosphate was calculated and the thermo­dynamic efficiency of the muscles was found to be high. On the basis of 10 kcal/mol adenosine triphosphate the overall efficiency was over 66 ± 6% at 2 cm/s in experiments with muscles pretreated with 2, 4-dinitrofluorobenzene. The amount of adenosine triphosphate used for processes other than mechanical work (mainly calcium pumping) was estimated to be about one quarter of the total. After allowance had been made for this the efficiency was found to be 98 ± 15% at a constant shortening velocity of 2 cm/s. Conversely, the minimum free energy available for doing external work from ATP hydrolysis under these conditions must be 9.8 ± 1.5 kcal/mol.

Translocators in Bimolecular Lipid Membranes: Their Role in Dissipative and Conservative Bioenergy Transductions

Abstract: Publisher Summary This chapter explains translocators in bimolecular lipid membranes: their role in dissipative and conservative bioenergy transductions. The theory is consistent with and relies heavily on findings in the ancillary fields of monolayer and surface chemistry. An ionic translocator mechanism is energized chemically to permit the synthesis of active transport and other bioenergy transductions in experimental lipid membranes. In an ideal situation, both the surface energies of the torus and of the bilayer are zero and the bilayer are torn or cut without retracting into the torus or forming a drop. The geometry and framing of the planar bilayer and the presence of special solvents create additional energy terms, which are absent in the spherical bilayers. When some lipid membranes are mechanically broken, they persist as sheets that do not contract into a drop. The extremely low ionic conductance of the bilayer must be attributed to the hydrocarbon region. Translocators show different degrees of functional complexity and are either simple or complex and show selectivity or variable dissociation for the translocated species and are also regulatable, that is, gated either by the translocated entity or by other agents. The energy conversions are linked to a central ion translocating system, which is capable of transporting ions against an electrochemical gradient

Hydrogen-Tritium Exchange of the Random Chain Polypeptide

Abstract: The Hydrogen–tritium exchange character of poly-D,L-alanine was studied in detail as a model for the hydrogen exchange behavior of the unhindered, polymeric peptide group. The random chain nature of poly-D,L-alanine was evident in the uniformity of exchange rate of all its hydrogens and in the similarity between this rate and that of random chain poly-D,L-lysine and other known, unhindered secondary amide groups. An equilibrium isotope effect favoring the binding of tritium over protium to the extent of 21% was measured. Specific acid and base catalysis of the exchange and the absence of detectable general catalysis were demonstrated. Apparent energy of activation is 17 kcal/mole for deprotonation, largely due to dependence of Kw on temperature, and 15 kcal/mole for protonation, which correlates with the extreme apparent pK. The hydrogen –tritium exchange half-time rate; of poly-D,L-alamine at any pH and temperature (T: °C) is given by the equation: