Showing papers by "Cornell University published in 1978"

Transformation of yeast

Abstract: A stable leu2- yeast strain has been transformed to LEU2+ by using a chimeric ColE1 plasmid carrying the yeast leu2 gene. We have used recently developed hybridization and restriction endonuclease mapping techniques to demonstrate directly the presence of the transforming DNA in the yeast genome and also to determine the arrangement of the sequences that were introduced. These studies show that ColE1 DNA together with the yeast sequences can integrate into the yeast chromosomes. This integration may be additive or substitutive. The bacterial plasmid sequences, once integrated, behave as a simple Mendelian element. In addition, we have determined the genetic linkage relationships for each newly introduced LEU2+ allele with the original leu2- allele. These studies show that the transforming squences integrate not only in the leu2 region but also in several other chromosomal locations.

Charmonium: The model

Abstract: A comprehensive treatment of the charmonium model of the ψ family is presented. The model's basic assumption is a flavor-symmetric instantaneous effective interaction between quark color densities. This interaction describes both quark-antiquark binding and pair creation, and thereby provides a unified approach for energies below and above the threshold for charmed-meson production. If coupling to decay channels is ignored, one obtains the “naive” model wherein the dynamics is completely described by a single charmed-quark pair. A detailed description of this “naive” model is presented for the case where the instantaneous potential is a superposition of a linear and Coulombic term. A far more realistic picture is attained by incorporating those terms in the interaction that couple charmed quarks to light quarks. The coupled-channel formalism needed for this purpose is fully described. Formulas are given for the inclusive e + e − cross section and for e + e − e annihilation into specific charmed-meson pairs. The influence of closed decay channels on ψ states below charm threshold is investigated, with particular attention to leptonic and radiative widths.

A simple dynamical model of intermittent fully developed turbulence

Abstract: We present a phenomenological model of intermittency called the P-model and related to the Novikov-Stewart (1964) model. The key assumption is that in scales N &2-” only a fraction /3n of the total space has an appreciable excitation. The model, the idea of which owes much to Kraichnan (1972, 1974)’ is dynamical in the sense that we work entirely with inertial-range quantities such as velocity amplitudes, eddy turnover times and energy transfer. This gives more physical insight than the traditional approach based on probabilistic models of the dissipation. The P-model leads in an elementary way to the concept of the self-similarity dimension D, a special case of Mandelbrot’s (1974, 1976) ‘fractal dimension’. For threedimensional turbulence, the correction B to the Q exponent of the energy spectrum is equal to +( 3 - D) and is related to the exponent p of the dissipation correlation function by B = Qp (0.17 for the currently accepted value). This is a borderline case of the Mandelbrot inequality B < Qp. It is shown in the appendix that this inequality may be derived from the Navier-Stokes equation under the strong, but plausible, assumption that the inertial-range scaling laws for second- and fourth-order moments have the same viscous cut-off. The predictions of the P-model for the spectrum and for higher-order statistics are in agreement with recent conjectures based on analogies with critical phenomena (Nelkin 1975) but generally diasgree with the 1962 Kolmogorov lognormal model. However, the sixth-order structure function (8v6(Z)) and the dissipation correlation function (e(r) e(r + 1)) are related by

Epidural spinal cord compression from metastatic tumor: Diagnosis and treatment

Abstract: The clinical findings in 130 conseucutive cases of spinal cord compression by metastatic extradural tumors were analyzed. These 130 patients were combined with a previous survey of 105 patients to compare the effectiveness of radiation therapy (RT) alone with that of surgical decompression followed by RT. Ambulation after treatment was considered a successful outcome. The most common primary tumors producing spinal cord compression were (in order) breast, lung, prostate, and kidney. In 68% of these tumors the thoracic region was involved. Pain was the primary symptom of 96% of the patients, while motor or sensory deficits (or both) were found in 82% of them. Therapy consisted of surgery and RT in 65 patients and RT alone in 170 patients. There were no differences in outcome between those treated by surgery combined with RT and those managed by RT alone. Patients with radiosensitive tumors and those ambulatory at the onset of treatment benefited whether treated by surgery or by RT. Seventy-five percent of living patients who improved from treatment remained ambulatory at 6 months, and approximately 50% of living patients were ambulatory at 1 year. We conclude that RT without decompressive laminectomy is as effective as decompressive laminectomy in treating epidural spinal cord compression from systemic cancer.

Computing integrals involving the matrix exponential

Abstract: A new algorithm for computing integrals involving the matrix exponential is given. The method employs diagonal Pade approximation with scaling and squaring. Rigorous truncation error bounds are given and incorporated in a Fortran subroutine. The computational aspects of this program are discussed and compared with existing techniques.

The structure of vortex breakdown

Abstract: The term 'vortex breakdown', as used in the reported investigation, refers to a disturbance characterized by the formation of an internal stagnation point on the vortex axis, followed by reversed flow in a region of limited axial extent. Two forms of vortex breakdown, which predominate, are shown in photographs. One form is called 'near-axisymmetric' (sometimes 'axisymmetric'), and the other is called 'spiral'. A survey is presented of work published since the 1972 review by Hall. Most experimental data taken since Hall's review have been in tubes, and the survey deals primarily with such cases. It is found that the assumption of axial-symmetry has produced useful results. The classification of flows as supercritical or subcritical, a step that assumes symmetry, has proved universally useful. Experiments show that vortex breakdown is always preceded by an upstream supercritical flow and followed by a subcritical wake. However, a comparison between experiments and attempts at prediction is less than encouraging. For a satisfactory understanding of the structure of vortex breakdown it is apparently necessary to take into account also aspects of asymmetry.

The Thomas and Cross Models of Psychological Nigrescence A Review

Abstract: Adult Black identity change that took place within the context of the recent Black sociopolitical movement is the focus of a literature review. The review summarizes two models that depict the various stages that might be associated with the psychological metamorphosis of Black Americans and examines the empirical studies that have been conducted to test the models. Although the models seem to predict major changes in both the self- concept and reference group orientation of converts, the empirical evidence suggests that only the reference group orientation of converts was subject to permanent modification.

A Model and an Algorithm for the Dynamic Traffic Assignment Problems

Abstract: A discrete time model is presented for dynamic traffice assignment with a single destination. Congestion is treated explicitly in the flow equations. The model is a nonlinear and nonconvex mathematical programming problem. A piecewise linear version of the model, with additional assumptions on the objective function, can be solved for a global optimum using a one-pass simplex algorithm---branch-and-bound is not required. The piecewise linear program has a staircase structure and can be solved by decomposition techniques or compactification methods for sparse matrices.

Best Algorithms for Approximating the Maximum of a Submodular Set Function

Abstract: A real-valued function z whose domain is all of the subsets of N = {1,..., n is said to be submodular if zS + zT ≥ zS ∪ T + zS ∩ T, ∀S, T ⊆ N, and nondecreasing if zS ≤ zT, ∀S ⊂ T ⊆ N. We consider the problem maxS⊂N {zS: |S| ≤ K, z submodular and nondecreasing, zO = 0}. Many combinatorial optimization problems can be posed in this framework. For example, a well-known location problem and the maximization of certain boolean polynomials are in this class. We present a family of algorithms that involve the partial enumeration of all sets of cardinality q and then a greedy selection of the remaining elements, q = 0,..., K-1. For fixed K, the qth member of this family requires Onq+1 computations and is guaranteed to achieve at least $$\biggl[1-\biggl\frac{K-q}{K}\biggr\biggl\frac{K-q-1}{K-q}\biggr^{K-q}\biggr]\times100 \quad\mbox {percent of the optimum value}.$$ Our main result is that this is the best performance guarantee that can be obtained by any algorithm whose number of computations does not exceed Onq+1.

Human Territoriality: An Ecological Reassessment

Abstract: The question of human territoriality has frequently been debated, but most previous discussions have not sufficiently emphasized ecological variables as major factors determining territoriality. We argue that current theories in sociobiology, especially the model focusing on economic defendability of resources, need to be considered in analyzing human territoriality. According to this model, territoriality is expected to occur when critical resources are sufficiently abundant and predictable in space and time, so that costs of exclusive use and defense of an area are outweighed by the benefits gained from resource control. This model is developed, and then applied to several locally adapted human populations (Northern Ojibwa, Basin-Plateau Indians, and Karimojong). Variations in territorial responses for these groups seem to accord with the predictions of the economic defendability model. [territoriality, resource defense, human ecology, sociobiology, spatial organization]

The Hadronic Properties of the Photon in High-Energy Interactions

Abstract: High-energy photon interactions are discussed in terms of the hadronic structure of the photon, which is expressed by means of a formulation which is akin to, but somewhat more general than, vector-meson-dominance or specific generalized vector-dominance models. Experiments which demonstrate and yield information about this hadronic structure are discussed critically, and the resulting information is carefully evaluated. Special attention is paid to diffractive processes such as the photoproduction of vector mesons and to photon shadowing effects on nuclei. Relationships to other views of photon interactions, such as the parton model and the space-time description, are also discussed; these views are seen to complement the hadronic structure picture rather than to be in conflict. The general overview is that there is ample evidence which shows that the photon's hadronic structure plays a significant role in its interactions. What further work would most significantly enhance the understanding of the hadronic structure of the photon is also pointed out.

Study of the Superfluid Transition in Two-Dimensional He 4 Films

Abstract: We have studied the superfluid transition of a thin two-dimensional helium film adsorbed on an oscillating substrate. The superfluid mass and dissipation when analyzed in terms of the dynamic theory of Ambegaokar, Halperin, Nelson, and Siggia support the Kosterlitz-Thouless picture of the phase transition in a two-dimensional superfluid. The value for the jump in the superfluid density at the transition given by Kosterlitz and Thouless, ${\ensuremath{\rho}}_{s}({{T}_{c}}^{\ensuremath{-}})=8\ensuremath{\pi}{k}_{\mathrm{B}}{(\frac{m}{h})}^{2}{T}_{c}$, is in good agreement with estimates from experiment.

Assessing personal, role, and organizational predictors of managerial commitment.

Abstract: Using a role and exchange theory framework, this study examines the commitment to their organization and to the federal service of 634 managers in 71 federal government organizations. Results indicate that certain role factors such as tenure and work overload and personal factors such as attitude toward change and job involvement are strong influences on commitment. Implications of the findings and the need for further theoretical and methodological refinements are discussed.

Sequence of the lacI gene.

Abstract: The structural gene for the lac repressor of Escherichia coli, the lacI gene has been sequenced. This 1,080 base pair region of the E. coli chromosome codes for the lac repressor protein of 360 amino acids. The DNA sequence largely confirms but extends the previously reported protein sequence and allows a structural analysis of genetic phenomena.

Yang-Lee Edge Singularity and ϕ 3 Field Theory

Abstract: The edge of the gap in the distribution of Yang-Lee zeros at $H=i{H}_{0}(T)$ on the imaginary magnetic field axis in ferromagnets above ${T}_{c}$ is essentially a critical point. In terms of the edge exponents $\ensuremath{\delta}$ and $\ensuremath{\eta}$, the density of zeros obeys $\mathcal{G}({H}^{\ensuremath{'}\ensuremath{'}})\ensuremath{\sim}{[{H}^{\ensuremath{'}\ensuremath{'}}\ensuremath{-}{H}_{0}(T)]}^{\ensuremath{\sigma}}$, with $\ensuremath{\sigma}=\frac{1}{\ensuremath{\delta}}=\frac{(d\ensuremath{-}2+\ensuremath{\eta})}{({d}_{2}\ensuremath{-}\ensuremath{\eta})}$. Classical behavior ($\ensuremath{\sigma}=\frac{1}{2}$) occurs for $dg{d}^{\ifmmode\times\else\texttimes\fi{}}=6$. The appropriate field-theoretic renormalization group entails a $w{\ensuremath{\phi}}^{3}$ coupling and, with $\ensuremath{\epsilon}=6\ensuremath{-}dg~0$, yields $\ensuremath{\eta}\ensuremath{\approx}\ensuremath{-}\frac{\ensuremath{\epsilon}}{9}$ for all $nl\ensuremath{\infty}$. This correlates well with refined series estimates for $d=2$ and $d=3$ and with exact results for $d=1$ ($\ensuremath{\eta}=\ensuremath{-}1$).

The Chain-of-Bundles Probability Model For the Strength of Fibrous Materials I: Analysis and Conjectures

Abstract: Analytical results are discussed for the chain-of-bundles probability model for the strength of fibrous materials. Two load sharing rules are considered for failed and nonfailed fibers in a bundle. The first is the equal load sharing rule of classical analysis, and the second is a local load sharing rule which is more realistic for composite materials. A rather detailed discussion of past statistical analysis is given. From a careful study of previous results, several conjectures and key questions about the behavior of the strength are generated. Also, an exact analysis of failure is per formed so that the properties of the strength distribution can be studied. Difficulties of a general analysis are discussed in detail. The sequel will contain a thorough numerical investigation of the model with emphasis on studying the convergence of certain transformed distributions and on answering key questions raised in this study.

An experimental study of the decay of temperature fluctuations in grid-generated turbulence

Abstract: Previous measurements of the decay rate of the fluctuation intensity of passive scalars in grid-generated turbulence show large variation. New results presented here show that the decay rate of passive temperature fluctuations produced by heating the grid is a function of the initial temperature fluctuation intensity. Although a full reason for this is wanting, spectra of the temperature fluctuations show that, by varying the heat applied to the grid, the wavenumber of the maximum in the temperature spectrum changes, indicating that the geometry of the thermal fluctuations is being altered in some way. In these experiments the one-dimensional temperature spectrum shows an anomalous slope. In order to eliminate the dependence of the decay rate of the temperature fluctuations on their intensity, we describe a new way of generating temperature fluctuations by means of placing a heated parallel array of fine wires (a mandoline) downstream from the unheated grid. Results of this experiment show that the decay rate of passive thermal fluctuations is uniquely determined by the wave-number of the initial temperature fluctuations. In this type of flow there appears to be no equilibrium value for the thermal fluctuation decay rate and hence for the mechanical/thermal time-scale ratio since the thermal fluctuation decay rate does not change within the tunnel length, which is the equivalent of nearly one turbulence decay time.

Optimality Conditions for a Dynamic Traffic Assignment Model

Abstract: We consider a dynamic traffic assignment model formulated as a nonlinear and noneonvex mathematical program. Necessary optimality conditions require equalization of certain marginal costs for all the paths that are being used, and these optimality conditions are shown to be a generalization of the optimality conditions of a conventional static traffic assignment problem. We also examine the behavior of the dynamic model under static demand conditions and show that in this case our model is a generalized version of a standard static model. Our model suggests a promising refinement of the objective function for the static case.

Color spaces for computer graphics

Abstract: Normal human color perception is a product of three independent sensory systems. By mirroring this mechanism, full-color display devices create colors as mixtures of three primaries. Any displayable color can be described by the corresponding values of these primaries. Frequently it is more convenient to define various other color spaces, or coordinate systems, for color representation or manipulation. Several such color spaces are presented which are suitable for applications involving user specification of color, along with the defining equations and illustrations. The use of special color spaces for particular kinds of color computations is discussed.

Universality aspects of the metal-nonmetal transition in condensed media

Abstract: Our objective in this paper is to provide a simple, conceptual, framework for describing the metalnonmetal (MNM) transition in systems that can be viewed in terms of a lattice of impurity states embedded in a host matrix. From an extensive analysis of experimental data, we find that a particular (scaled) form of the Mott criterion, ${n}_{c}^{\frac{1}{3}}{a}_{H}^{*}=0.26\ifmmode\pm\else\textpm\fi{}0.05$, is applicable over a range of approximately ${10}^{10}$ in critical densities (${n}_{c}$) and approximately 600 \AA{} in Bohr radii (${a}_{H}^{*}$). Here ${a}_{H}^{*}$ is defined as an appropriate radius associated with a realistic wave function for the localized state in the low-electron-density regime. The systems of interest range from tight-binding (Frenkel) metal-atom states in the rare-gas solids to shallow (Wannier-like) states in the group-IV $a$ semiconductors and indium antimonide. The possible origins of this apparent universality have been formulated from a consideration of Berggren's interpretation of the Hubbard model for the transition, as applied to condensed systems. In essence, it appears that the role of the host matrix in the phenomenon of MNM transition is important primarily in the sense that it determines the form of the radial distribution of the (localized) impurity state. We suggest that once these matrix-induced modifications to the (gas-phase) donor state are taken into account, the ensuing transition to the metallic state (at finite impurity concentrations) reduces to a one-electron problem in a suitably renormalized concentration grid.

Unstable angina pectoris: National cooperative study group to compare surgical and medical therapy: II. In-Hospital experience and initial follow-up results in patients with one, two and three vessel disease

Abstract: A prospective randomized study comparing intensive medical therapy with urgent coronary bypass surgery for the acute management of patients with unstable angina pectoris was carried out by nine cooperating medical centers under the auspices of the National Heart, Lung, and Blood Institute. Between 1972 and 1976, a total of 288 patients were entered into the study. All patients had transient S-T or T wave changes, or both, in the electrocardiogram during pain; 90 percent had pain at rest in the hospital, and 76 percent had multivessel coronary disease. The medically and surgically treated patients were comparable with respect to clinical, electrocardiographic and angiographic characteristics and left ventricular function. During the total study period, the hospital mortality rate was 5 percent in the surgical group and 3 percent in the medical group (difference not significant). The rate of in-hospital myocardial infarction was 17 and 8 percent in the respective groups (P In the 1st year after hospital discharge class III or IV angina (New York Heart Association criteria) was more common in medically than in surgically treated patients with one vessel disease (22 percent versus 3 percent, P The results indicate that patients with unstable angina pectoris can be managed acutely with intensive medical therapy, including the administration of propranolol and long-acting nitrates in pharmacologic doses, with adequate control of pain in most patients and no increase in early mortality or myocardial infarction rates. Later, elective surgery can be performed with a low risk and good clinical results if the patient's angina fails to respond to intensive medical therapy.