Showing papers by "Massachusetts Institute of Technology published in 1970"
TL;DR: Two independent groups of investigators have found evidence of an enzyme in virions of RNA tumour viruses which synthesizes DNA from an RNA template, apparently the classical process of information transfer from DNA to RNA can be inverted.
Abstract: Two independent groups of investigators have found evidence of an enzyme in virions of RNA tumour viruses which synthesizes DNA from an RNA template. This discovery, if upheld, will have important implications not only for carcinogenesis by RNA viruses but also for the general understanding of genetic transcription: apparently the classical process of information transfer from DNA to RNA can be inverted.
1,872 citations
Book•
01 Jan 1970TL;DR: The second edition of this classic book as discussed by the authors provides an updated look at crystal field theory and its applications and highlights the properties of minerals that make them compounds of interest to solid-state chemists and physicists as well as to all earth and planetary scientists.
Abstract: The second edition of this classic book provides an updated look at crystal field theory - one of the simplest models of chemical bonding - and its applications. Crystal field theory provides a link between the visible region spectra and thermodynamic properties of numerous rock-forming minerals and gems that contain the elements iron, titanium, vanadium, chromium, manganese, cobalt, nickel or copper. These elements are major constituents of terrestrial planets and significantly influence their geochemical and geophysical properties. A unique perspective of the second edition is that it highlights the properties of minerals that make them compounds of interest to solid-state chemists and physicists as well as to all earth and planetary scientists. This book will be useful as a textbook for advanced students as well as a valuable reference work for all research workers interested in this subject.
1,479 citations
TL;DR: In this article, a resonant post technique for characterizing dielectric and magnetic materials at microwave frequencies was proposed and experimental results of the temperature dependence of the relative dielectrics constant of nonmagnetic materials with /spl epsilon/sub r/, varying from 4 to 60, and also loss tangent measurements at room temperature.
Abstract: Theory and experimental results are presented to show the possibility of using a resonant post technique for characterizing dielectric and magnetic materials at microwave frequencies. Results of the temperature dependence of the relative dielectric constant of nonmagnetic materials with /spl epsilon//sub r/, varying from 4 to 60 are presented and also loss tangent measurements at room temperature. The complex permittivity and permeability of a number of garnet materials has also been measured with 4/spl pi//spl gamma/M/sub s/ / /spl omega/ varying from 0.25 to 0.8. The measured real part of the permeability is in good agreement with the theoretical predictions of Schlomann and the imaginary part of the permeability agrees with measurements by Green et al. on similar materials.
1,247 citations
TL;DR: Discussions center on the general nature of the problem, mathematical modeling, an interative technique for calculating the state estimate, and concepts underlying the detection and identification of modeling errors.
Abstract: The static state of an electric power system is defined as the vector of the voltage magnitudes and angles at all network buses The static-state estimator is a data processing algorithm far converting redundant meter readings and other available information into an estimate of the static-state vector Discussions center on the general nature of the problem, mathematical modeling, an interative technique for calculating the state estimate, and concepts underlying the detection and identification of modeling errors Problems of interconnected systems are considered Results of some initial computer simulation tests are discussed
1,227 citations
TL;DR: The mechanics of the knee joint were simplified and defined in mathematical terms and the assumptions made in defining the joint ‘model’ described were discussed.
1,037 citations
TL;DR: In this paper, it was shown that the matrix elements of the symmetric energy-momentum tensor are cut-off dependent in renormalized perturbation theory for most renormalizable field theories.
1,002 citations
TL;DR: In this article, the optimal control of linear time-invariant systems with respect to a quadratic performance criterion is discussed and an algorithm for computing FAST is presented.
Abstract: The optimal control of linear time-invariant systems with respect to a quadratic performance criterion is discussed. The problem is posed with the additional constraint that the control vector u(t) is a linear time-invariant function of the output vector y(t) (u(t) = -Fy(t)) rather than of the state vector x(t) . The performance criterion is then averaged, and algebraic necessary conditions for a minimizing F\ast are found. In addition, an algorithm for computing F\ast is presented.
906 citations
TL;DR: In this article, the authors provide a mathematical framework for the process of making repeated measurements on continuous observables in a statistical system and make a mathematical definition of an instrument, a concept which generalises the notion of an observable and that of an operation.
Abstract: In order to provide a mathmatical framework for the process of making repeated measurements on continuous observables in a statistical system we make a mathematical definition of an instrument, a concept which generalises that of an observable and that of an operation. It is then possible to develop such notions as joint and conditional probabilities without any of the commutation conditions needed in the approach via observables. One of the crucial notions is that of repeatability which we show is implicitly assumed in most of the axiomatic treatments of quantum mechanics, but whose abandonment leads to a much more flexible approach to measurement theory.
890 citations
TL;DR: An optimum rejection rule is described and a general relation between the error and reject probabilities and some simple properties of the tradeoff in the optimum recognition system are presented.
Abstract: The performance of a pattern recognition system is characterized by its error and reject tradeoff. This paper describes an optimum rejection rule and presents a general relation between the error and reject probabilities and some simple properties of the tradeoff in the optimum recognition system. The error rate can be directly evaluated from the reject function. Some practical implications of the results are discussed. Examples in normal distributions and uniform distributions are given.
841 citations
TL;DR: In this paper, a thermodynamic model which predicts the properties of the burnt and unburnt gases during the combustion process is developed, and rate equations for nitric oxide concentrations as a function of time in the post-flame gases are derived.
Abstract: The nonequilibrium formation of nitric oxide within the internal combustion engine cylinder is examined. A thermodynamic model which predicts the properties of the burnt and unburnt gases during the combustion process is developed. A set of reactions which govern the formation of nitric oxide is proposed, and rate equations for nitric oxide concentrations as a function of time in the post-flame gases are derived. The results of time-resolved measurements carried out on a CFR engine are described, where emitted light intensities at wavelengths selected to record radiation from the CO + O and NO + O continua were used to determine the nitric oxide concentration. The comparison between theoretical and experimental results for fuel-lean mixtures confirms that the important features of the model presented are correct.
763 citations
TL;DR: In this paper, the authors present an alternative way to relate the expected utility and mean-variance approaches, and present proofs of the usefulness of mean and variance in situations involving less and less risk.
Abstract: Publisher Summary The chapter presents an alternative way to relate the expected utility and mean-variance approaches. It presents proofs of the two general theorems involved in an aspect of the mean-variance model—namely, the usefulness of mean and variance in situations involving less and less risk. It describes a defense of mean-variance analysis and highlights its exact limitations along with those for any r-moment model. The mean and variance of wealth are approximately sufficient parameters for the portfolio selection model when the probability distribution of wealth is compact. In the compact case, moments of order 3 and higher are small in magnitude relative to the first two moments of the portfolio return; hence, a limiting approximation indicates that only the first two moments are relevant for optimal portfolio selection.
01 Jan 1970
TL;DR: In this paper, a model is defined as a solution of the equations that describe the system under consideration, i.e., a solution to the equations governing a system as complex as the magnetosphere is clearly impossible, and to construct a theoretical model the equations must be simplified to the point of tractability.
Abstract: The phrase ‘magnetospheric model’ can have several different meanings. Here I am using the term ‘model’ in the sense described by Parker (1968): “We construct idealized and simplified theoretical models for the purpose of demonstrating how the basic laws of physics lead to a certain observed effect.” A model in this sense is a solution of the equations that describe the system under consideration. Obtaining an exact solution of the equations governing a system as complex as the magnetosphere is clearly impossible, and to construct a theoretical model the equations must be simplified (often drastically) to the point of tractability. The aim is to isolate those aspects of the physical situation that are essential to the particular phenomenon one is attempting to understand. One thus proceeds by solving the basic equations under a variety of simplifying assumptions and noting what assumptions are required to reproduce the essential features of the phenomenon under study. Of course, no model will predict in precise quantitative detail all the features of the observations, but then our primary goal is understanding, not forecasting.
TL;DR: In this paper, a model for determining the density of states of pure stoichiometric NiO is proposed, taking into account the free-ion energy levels, and taking the Madelung potential, screening and covalency effects, crystalline-field stabilizations, and overlap effects.
Abstract: The electrical and optical properties of materials which are characterized by narrow bands in the vicinity of the Fermi energy are discussed. For such materials, electronic correlations and the electron-phonon coupling must be considered explicitly. Correlations in $f$ bands and in extremely narrow $d$ bands can be handled in the ionic limit of the Hubbard Hamiltonian. It is shown that free carriers in such bands form small polarons which contribute to conduction only by means of thermally activated hopping. Wider bands may also exist near the Fermi energy. Carriers in these bands may form large polarons and give a bandlike contribution to conductivity. A model is proposed for determining the density of states of pure stoichiometric crystals, beginning with the free-ion energy levels, and taking into account the Madelung potential, screening and covalency effects, crystalline-field stabilizations, and overlap effects. Exciton states are considered explicitly. The Franck-Condon principle necessitates the construction of different densities of states for electrical conductivity and optical absorption. Because of the bulk of experimental data presently available, the model is applied primarily to NiO. The many-particle density of states of pure stoichiometric NiO is calculated and is shown to be in agreement with the available experimental data. When impurities are present or nonstoichiometry exists, additional transitions must be discussed from first principles. The case of Li-doped NiO is discussed in detail. The calculations are consistent with the large mass of experimental information on this material. It is concluded that the predominant mechanism for conduction between 200 and 1000 \ifmmode^\circ\else\textdegree\fi{}K is the transport of hole-like large polarons in the oxygen $2p$ band. A method for representing the many-particle density of states on an effective one-electron diagram is discussed. It is shown that if correlations are important, donor or acceptor levels cannot be drawn as localized levels in the energy gap when multiple conduction or valence bands are present. This result comes about because extrinsic ionization energies of two correlated bands differ by an energy which bears no simple relation to the difference in energies of the intrinsic excitations, which are conventionally used to determine the relative positions of the bands.
TL;DR: Comparison with laboratory measurements on meteorites and Apollo 11 samples indicates that the surface of Vesta has a composition very similar to that of certain basaltic achondrites.
Abstract: The spectral reflectivity (0.30 to 1.10 microns) of several asteroids has been measured for the first time. The reflection spectrum for Vesta contains a strong absorption band centered near 0.9 micron and a weaker absorption feature between 0.5 and 0.6 micron. The reflectivity decreases strongly in the ultraviolet. The reflection spectrum for the asteroid Pallas and probably for Ceres does not contain the 0.9-micron band. Vesta shows the strongest and best-defined absorption bands yet seen in the reflection spectrum for the solid surface of an object in the solar system. The strong 0.9-micron band arises from electronic absorptions in ferrous iron on the M2 site of a magnesian pyroxene. Comparison with laboratory measurements on meteorites and Apollo 11 samples indicates that the surface of Vesta has a composition very similar to that of certain basaltic achondrites.
TL;DR: Preparations of many different types of viruses contain defective particles which consist of viral structural proteins and a part of the viral genome and may play a major part in the evolution of viral diseases.
Abstract: Preparations of many different types of viruses contain defective particles which consist of viral structural proteins and a part of the viral genome. Such particles are capable of specifically interfering with the growth of homologous, standard virus and may play a major part in the evolution of viral diseases.
TL;DR: In this paper, the authors define a graded ring K, F associated to any rational function field F and construct a homomorphism associated with a discrete valuation on F with residue class field F.
Abstract: The first section of this paper defines and studies a graded ring K . F associated to any field F. By definition, K~F is the target group of the universal n-linear function from F ~ x ... • F ~ to an additive group, satisfying the condition that al • " ' x a, should map to zero whenever a i -q-a i + ~ = 1. Here F ~ denotes the multiplicative group F 0 . Section 2 constructs a homomorphism ~: K,F---, K~__I_~ associated with a discrete valuation on F with residue class field F. These homomorphisms ~ are used to compute the ring K, F(t) of a rational function field, using a technique due to John Tate. Section 3 relates K . F to the theory of quadratic modules by defining certain " Stiefel-Whitney invariants" of a quadratic module over a field F of characteristic . 2 . The definition is closely related to Delzant [-5]. Let W be the Witt ring of anisotropic quadratic modules over F, and let I c W be the maximal ideal, consisting of modules of even rank. Section 4 studies the conjecture that the associated graded ring
TL;DR: In this article, a simple general relation for bubble growth rates in a uniformly superheated liquid was derived, and the relation was valid in both regions: inertia controlled and heat diffusion controlled growth, respectively.
TL;DR: In this article, the authors measured the linewidth and the frequency of the q = 0 optical phonon in silicon over the temperature range of 20-770, and deduced an absolute halfwidth of 2.1
Abstract: We have measured the linewidth and the frequency of the q=0 optical phonon in silicon over the temperature range of 20-770\ifmmode^\circ\else\textdegree\fi{}K. The temperature dependence of the linewidth has been interpreted as arising from the decay of the optical phonon to two LA phonons at half the optical frequency. From the observed temperature variation, we deduce an absolute half-width $\ensuremath{\Gamma}$ of 2.1 ${\mathrm{cm}}^{\ensuremath{-}1}$ at 0\ifmmode^\circ\else\textdegree\fi{}K. This value is considerably smaller than that obtained theoretically by Cowley on the basis of numerical calculations which include decay to phonons throughout the Brillouin zone. His numerical calculations also predict a temperature dependence of the linewidth which does not agree with experiment. However, the observed change in frequency with temperature correlates very well with Cowley's theory. We have also studied the relative intensities of Stokes and anti-Stokes components of Raman spectra. The observed temperature dependence of the relative intensities is compared with that predicted on the basis of the Bose-Einstein population factor for the optical phonon.
TL;DR: In this paper, the authors present a hypothesis regarding the causes of agricultural serfdom or slavery. But the hypothesis is limited to the Russian experience in the sixteenth and seventeenth centuries, and it aims at a wider applicability.
Abstract: The purpose of this paper is to present, or more correctly, to revive, a hypothesis regarding the causes of agricultural serfdom or slavery (used here interchangeably). The hypothesis was suggested by Kliuchevsky's description of the Russian experience in the sixteenth and seventeenth centuries, but it aims at a wider applicability.
TL;DR: It appears that the reduced protein synthesis during mitosis results from a lowered rate of attachment of ribosomes to messenger RNA and initiation of polypeptide synthesis.
TL;DR: An approximate mathematical model related to the dc load-flow model yields noniterative-state estimation equations, simplified prediction of effects of network and generation-load pattern changes on network flow, and simplified detection and identification of modeling errors.
Abstract: The static state of an electric power system is defined as the vector of the voltage magnitudes and angles at all network buses. The static-state estimator is a data-processing algorithm for converting redundant meter readings and other available information into an estimate of the static-state vector. Discussions center on an approximate mathematical model (related to the dc load-flow model). This model yields noniterative-state estimation equations, simplified prediction of effects of network and generation-load pattern changes on network flow, and simplified detection and identification of modeling errors. Results of some initial computer studies on the real power-voltage angle portion of the approximate model are discussed.
TL;DR: Discussions center on implementation problems associated with computation time requirements, dimensionality resulting from a large number of buses, and the actual time-varying (nonstatic) character of power systems.
Abstract: The static state of an electric power system is defined as the vector of the voltage magnitudes and angles at all network buses. The static-state estimator is a data processing algorithm for converting redundant meter readings and other available information into an estimate of the static-state vector. Discussions center on implementation problems associated with computation time requirements, dimensionality resulting from a large number of buses, and the actual time-varying (nonstatic) character of power systems. Various potentially useful approaches are discussed and compared.
TL;DR: Communication networks in R & D laboratories are shown to have structural characteristics, which when properly understood can be employed to more effectively maintain the laboratories' personnel abreast of technological developments.
Abstract: Communication networks in R & D laboratories are shown to have structural characteristics, which when properly understood can be employed to more effectively maintain the laboratories' personnel abreast of technological developments. Informal relations and physical location are shown to be important determinants of this structure. Informal relations can be developed through formation of project teams and intergroup transfers and loans. The effect of physical location on communications is especially strong and should be given serious consideration when designing research facilities.
TL;DR: In this paper, the authors propose a reduction to the Hermitian Hyperbolic case and derive the Conical Functions and Finite-Dimensional Representations of X and S.
TL;DR: In this article, the authors discussed the nature of damping mechanisms and how the damping depends on the amplitude and frequency of the cyclic motion of the system. But they did not consider the effect of the frequency and amplitude on damping.
TL;DR: In this article, it was shown that in a rotating stratified fluid bounded by a single rigid wall, edge waves may occur at all frequencies less than or equal to N sin a (a is the angle of the wall from the horizontal and N the Brunt Vaisala frequency).
Abstract: It is found that in a rotating stratified fluid bounded by a single rigid wall, edge waves may occur at all frequencies less than or equal to N sin a (a is the angle of the wall from the horizontal and N the Brunt‐Vaisala frequency). These decay exponentially away from the boundary, in a distance of O(S) wavelengths, for α = O(1), or O(S ‐1) wavelengths, for αS ≤ O(1), where S is the ratio of N to the Coriolis parameter f, taken for illustration to be large. The phase and energy both move with a component to the left, facing shallow water. The waves could, for example, appear as an internal tide at the continental rise or as baroclinic meandering of currents over a slope. The low‐frequency limit, αS ≪ 1, is studied in detail. To allow for large scales of motion other rigid boundaries and variations in f are included. The edge (actually “bottom") waves then merge with topographic‐planetary waves as the wavelengths increase; the familiar depth‐independent mode is found to be possible in the sea for...
TL;DR: Relationships between the probability of error, the equivocation, and the Chernoff bound are examined for the two-hypothesis decision problem and the results are extended to the case of any finite number of hypotheses.
Abstract: Relationships between the probability of error, the equivocation, and the Chernoff bound are examined for the two-hypothesis decision problem. The effect of rejections on these bounds is derived. Finally, the results are extended to the case of any finite number of hypotheses.
TL;DR: The results support the notion that, among the disorders caused by right posterior injuries, there does exist a material-specific deficit in recognizing faces.
TL;DR: Laser-excited Raman spectra of a simple native protein, lysozyme, in aqueous solution are reported and partially interpreted with the help of the specta of its constituent amino acids and appear to be potentially useful in assessment of conformational changes caused by denaturation.
TL;DR: Structural similarities between different poliovirus-specific polypeptides have been investigated by chromatography of tryptic hydrolysates of pairs of differentially-labeled proteins and suggest that the procapsid protein, VP-0, is cleaved into two of the virion proteins,VP-2 and -4.