Showing papers by "Harvard University published in 1969"

Proposed Experiment to Test Local Hidden Variable Theories.

Abstract: A theorem of Bell, proving that certain predictions of quantum mechanics are inconsistent with the entire family of local hidden-variable theories, is generalized so as to apply to realizable experiments. A proposed extension of the experiment of Kocher and Commins, on the polarization correlation of a pair of optical photons, will provide a decisive test between quantum mechanics and local hidden-variable theories.

Traumatic arthritis of the hip after dislocation and acetabular fractures: treatment by mold arthroplasty. An end-result study using a new method of result evaluation

Abstract: An end-result analysis is presented of thirty-nine mold arthroplasties performed at the Massachusetts General Hospital between 1945 and 1965 in thirty-eight consecutive private patients for arthritis of the hip following fractures of the acetabulum or dislocations of the hip. Of the nineteen unilateral cases in the second half of the series, sixteen were rated good or excellent. Results in the second half of the series were significantly better statistically than those in the first half of the series. Possible reasons for this improvement are discussed. No significant deterioration occurred with the passage of time. Among the thirty-nine hips, three revisions were required. One patient had postoperative sepsis after arthroplasty. Four patients who had had intra-articular sepsis prior to arthroplasty showed no evidence of sepsis postoperatively. Factors influencing the choice between hip fusion and hip arthroplasty in these cases are presented. A new system for rating hip function is proposed and is compared with the systems of Larson and Shepherd.

A PCAC puzzle: π0→γγ in the σ-model

Abstract: The effective coupling constant for π0→γγ should vanish for zero pion mass in theories with PCAC and gauge invariance. It does not so vanish in an explicit perturbation calculation in the σ-model. The resolution of the puzzle is effected by a modification of Pauli-Villars-Gupta regularization which respects both PCAC and gauge invariance.

Under what conditions can a glass be formed

Abstract: Summary Generally substances are more stable in a crystalline than in a glassy state. Therefore, to form a glass, crystallization must be bypassed. Under certain conditions, the melts of many substances can be cooled to the glass state. Whether or not the melt of a given material forms a glass is determined principally by a set of factors which can be specified to some extent in the laboratory, namely, the cooling rate, - T, the liquid volume, v], and the seed density, ps and upon a set of materials constants: the reduced crystal–liquid interfacial tension, α the fraction, f, of acceptor sites in the crystal surface, and the reduced glass temperature, Trg . The glass-forming tendency will be greater the larger are - T and Trg and the smaller are v]. ps, and f. The number and variety of substances which have been prepared in a glassy or ‘amorphous solid’ form have been greatly increased with techniques in which the material is condensed from solution on to a surface held well below its glass temperature. T...

An Experimental Study of the Small World Problem

Abstract: Arbitrarily selected individuals (N=296) in Nebraska and Boston are asked to generate acquaintance chains to a target person in Massachusetts, employing “the small world method” (Milgram, 1967). Sixty-four chains reach the target person. Within this group the mean number of intermediaries between starters and targets is 5.2. Boston starting chains reach the target person with fewer intermediaries than those starting in Nebraska; subpopulations in the Nebraska group do not differ among themselves. The funneling of chains through sociometric “stars” is noted, with 48 per cent of the chains passing through three persons before reaching the target. Applications of the method to studies of large scale social structure are discussed.

Structure of phenomenological lagrangians. ii.

Abstract: The general method for constructing invariant phenomenological Lagrangians is described. The fields are assumed to transform according to (nonlinear) realizations of an internal symmetry group, given in standard form. The construction proceeds through the introduction of covariant derivatives, which are standard forms for the field gradients. The case of gauge fields is also discussed.

The Unbound Prometheus: Technological Change and Industrial Development in Western Europe from 1750 to the Present

Abstract: Preface to the new edition Preface to the original edition 1. Introduction 2. The industrial revolution in Britain 3. Continental emulation 4. Closing the gap 5. Short breath and second wind 6. The interwar years 7. Reconstruction and growth since 1945 8. Conclusion 9. Epilogue Index.

Conceptual models and the Cuban missile crisis

Abstract: The Cuban missile crisis is a seminal event. For thirteen days of October 1962, there was a higher probability that more human lives would end suddenly than ever before in history. Had the worst occurred, the death of 100 million Americans, over 100 million Russians, and millions of Europeans as well would make previous natural calamities and inhumanities appear insignificant. Given the probability of disaster—which President Kennedy estimated as “between 1 out of 3 and even”—our escape seems awesome. This event symbolizes a central, if only partially thinkable, fact about our existence. That such consequences could follow from the choices and actions of national governments obliges students of government as well as participants in governance to think hard about these problems.Improved understanding of this crisis depends in part on more information and more probing analyses of available evidence. To contribute to these efforts is part of the purpose of this study. But here the missile crisis serves primarily as grist for a more general investigation. This study proceeds from the premise that marked improvement in our understanding of such events depends critically on more self-consciousness about what observers bring to the analysis. What each analyst sees and judges to be important is a function not only of the evidence about what happened but also of the “conceptual lenses” through which he looks at the evidence. The principal purpose of this essay is to explore some of the fundamental assumptions and categories employed by analysts in thinking about problems of governmental behavior, especially in foreign and military affairs.

Density operators and quasiprobability distributions.

Abstract: The problem of expanding a density operator $\ensuremath{\rho}$ in forms that simplify the evaluation of important classes of quantum-mechanical expectation values is studied. The weight function $P(\ensuremath{\alpha})$ of the $P$ representation, the Wigner distribution $W(\ensuremath{\alpha})$, and the function $〈\ensuremath{\alpha}|\ensuremath{\rho}|\ensuremath{\alpha}〉$, where $|\ensuremath{\alpha}〉$ is a coherent state, are discussed from a unified point of view. Each of these quasiprobability distributions is examined as the expectation value of a Hermitian operator, as the weight function of an integral representation for the density operator and as the function associated with the density operator by one of the operator-function correspondences defined in the preceding paper. The weight function $P(\ensuremath{\alpha})$ of the $P$ representation is shown to be the expectation value of a Hermitian operator all of whose eigenvalues are infinite. The existence of the function $P(\ensuremath{\alpha})$ as an infinitely differentiable function is found to be equivalent to the existence of a well-defined antinormally ordered series expansion for the density operator in powers of the annihilation and creation operators $a$ and ${a}^{\ifmmode\dagger\else\textdagger\fi{}}$. The Wigner distribution $W(\ensuremath{\alpha})$ is shown to be a continuous, uniformly bounded, square-integrable weight function for an integral expansion of the density operator and to be the function associated with the symmetrically ordered power-series expansion of the density operator. The function $〈\ensuremath{\alpha}|\ensuremath{\rho}|\ensuremath{\alpha}〉$, which is infinitely differentiable, corresponds to the normally ordered form of the density operator. Its use as a weight function in an integral expansion of the density operator is shown to involve singularities that are closely related to those which occur in the $P$ representation. A parametrized integral expansion of the density operator is introduced in which the weight function $W(\ensuremath{\alpha},s)$ may be identified with the weight function $P(\ensuremath{\alpha})$ of the $P$ representation, with the Wigner distribution $W(\ensuremath{\alpha})$, and with the function $〈\ensuremath{\alpha}|\ensuremath{\rho}|\ensuremath{\alpha}〉$ when the order parameter $s$ assumes the values $s=+1, 0, \ensuremath{-}1$, respectively. The function $W(\ensuremath{\alpha},s)$ is shown to be the expectation value of the ordered operator analog of the $\ensuremath{\delta}$ function defined in the preceding paper. This operator is in the trace class for $\mathrm{Res}l0$, has bounded eigenvalues for $\mathrm{Res}=0$, and has infinite eigenvalues for $s=1$. Marked changes in the properties of the quasiprobability distribution $W(\ensuremath{\alpha},s)$ are exhibited as the order parameter $s$ is varied continuously from $s=\ensuremath{-}1$, corresponding to the function $〈\ensuremath{\alpha}|\ensuremath{\rho}|\ensuremath{\alpha}〉$, to $s=+1$, corresponding to the function $P(\ensuremath{\alpha})$. Methods for constructing these functions and for using them to compute expectation values are presented and illustrated with several examples. One of these examples leads to a physical characterization of the density operators for which the $P$ representation is appropriate.

Factor stimulating transcription by RNA polymerase.

Abstract: A protein component usually associated with RNA polymerase can be separated from the enzyme by chromatography on phosphocellulose. The polymerase is unable to transcribe T4 DNA unless this factor is added back.

Piezoelectric Effects in Liquid Crystals

Abstract: A theory of the relationship between curvature strains and electric polarization in liquid crystals is developed in analogy to piezoelectric theory in ordinary crystals. The theory may explain some recently observed phenomena in nematic liquid crystals.

Singularities in the X-Ray Absorption and Emission of Metals. III. One-Body Theory Exact Solution

Abstract: The singularities of x-ray absorption or emission in metals are studied by a new "one-body" method, which describes the scattering of conduction electrons by the transient potential due to the deep hole. Using the linked-cluster theorem, the net transition rate in the time representation is expressed as the product of two factors: a one-electron transient Green's function $L$, and the deep-level Green's function $\mathcal{G}$. These factors obey simple Dyson equations, which can be solved asymptotically by using Muskhelishvili's method. The x-ray transition rate is found to behave as $\frac{1}{{\ensuremath{\epsilon}}^{\ensuremath{\alpha}}}$, where $\ensuremath{\epsilon}$ is the frequency measured from the threshold, and $\ensuremath{\alpha}$ an exponent involving the various phase shifts ${\ensuremath{\delta}}_{l}$ which describe scattering by the deep hole. $\ensuremath{\alpha}$ may be g0 (infinite threshold) or 0 (zero threshold). The experimental implications of these results and their relation to the Friedel sum rule are briefly discussed.

Ordered Expansions in Boson Amplitude Operators

Abstract: The expansion of operators as ordered power series in the annihilation and creation operators $a$ and ${a}^{\ifmmode\dagger\else\textdagger\fi{}}$ is examined. It is found that normally ordered power series exist and converge quite generally, but that for the case of antinormal ordering the required $c$-number coefficients are infinite for important classes of operators. A parametric ordering convention is introduced according to which normal, symmetric, and antinormal ordering correspond to the values $s=+1,0,\ensuremath{-}1$, respectively, of an order parameter $s$. In terms of this convention it is shown that for bounded operators the coefficients are finite when $sg0$, and the series are convergent when $sg\frac{1}{2}$. For each value of the order parameter $s$, a correspondence between operators and $c$-number functions is defined. Each correspondence is one-to-one and has the property that the function $f(\ensuremath{\alpha})$ associated with a given operator $F$ is the one which results when the operators $a$ and ${a}^{\ifmmode\dagger\else\textdagger\fi{}}$ occurring in the ordered power series for $F$ are replaced by their complex eigenvalues $\ensuremath{\alpha}$ and ${\ensuremath{\alpha}}^{*}$. The correspondence which is realized for symmetric ordering is the Weyl correspondence. The operators associated by each correspondence with the set of $\ensuremath{\delta}$ functions on the complex plane are discussed in detail. They are shown to furnish, for each ordering, an operator basis for an integral representation for arbitrary operators. The weight functions in these representations are simply the functions that correspond to the operators being expanded. The representation distinguished by antinormal ordering expresses operators as integrals of projection operators upon the coherent states, which is the form taken by the $P$ representation for the particular case of the density operator. The properties of the full set of representations are discussed and are shown to vary markedly with the order parameter $s$.

ENDOTHELIAL CONTRACTION INDUCED BY HISTAMINE-TYPE MEDIATORS : An Electron Microscopic Study

Abstract: Previous work has shown that endogenous chemical mediators, of which histamine is the prototype, increase the permeability of blood vessels by causing gaps to appear between endothelial cells. In the present paper, morphologic and statistical evidence is presented, to suggest that endothelial cells contract under the influence of mediators, and that this contraction causes the formation of intercellular gaps. Histamine, serotonin, and bradykinin were injected subcutaneously into the scrotum of the rat, and the vessels of the underlying cremaster muscle were examined by electron microscopy. To eliminate the vascular collapse induced by routine fixation, in one series of animals (including controls) the root of the cremaster was constricted for 2–4 min prior to sacrifice, and the tissues were fixed under conditions of mild venous congestion. Electron micrographs were taken of 599 nuclei from the endothelium of small blood vessels representing the various experimental situations. Nuclear deformations were classified into four types of increasing tightness (notches, foldsl closing folds, and pinches. In the latter the apposed surfaces of the nuclear membrane are in contact). It was found that: (1) venous congestion tends to straighten the nuclei in al groups; (2) mediators cause a highly significant increase in the number of pinches (P < 0.001), also if the vessels are distended by venous congestion; (3) fixation without venous congestion causes vascular collapse. The degree of endothelial recoil, as measured by nuclear pinches, is very different from that caused by mediators (P < 0.001). (4) Pinched nuclei are more frequent in leaking vessels, and in cells adjacent to gaps (P < 0.001); (5) mediators also induce, in the endothelium, cytoplasmic changes suggestive of contraction, and similar to those of contracted smooth muscle; (6) there is no evidence of pericyte contraction under the conditions tested. Occasional pericytes appeared to receive fine nerve endings. Various hypotheses to explain nuclear pinching are discussed; the only satisfactory explanation is that which requires endothelial contraction.

Termination Factor for RNA Synthesis

Abstract: A new protein has been isolated from E. coli which causes specific termination and release of RNA during synthesis in vitro. It has been given the name ρ-factor.

Nonzero-sum differential games

Abstract: Differential games theory with nonzero sum for application to economic analysis, discussing Nash equilibrium, minimax and noninferior strategies set

Choice as time allocation.

Abstract: When pigeons' standing on one or the other side of a chamber was reinforced on two concurrent variable-interval schedules, the ratio of time spent on the left to time spent on the right was directly proportional to the ratio of reinforcements produced by standing on the left to reinforcements produced by standing on the right. The constant of proportionality was less than unity for all pigeons, indicating a bias toward the right side of the chamber. The biased matching relation obtained here is comparable to the matching relation obtained with concurrent reinforcement of key pecks. The present results, together with related research, suggest that the ratio of time spent in two activities equals the ratio of the "values" of the activities. The value of an activity is the product of several parameters, such as rate and amount of reinforcement, contingent on that activity.

The arterial lesions underlying lacunes.

Abstract: The arterial lesions causing lacunes have been investigated using serial sections of blocks of the basal ganglia and pons from four cases with a history of hypertension and small strokes. In 45 of 50 consecutive lacunes there was a total occlusion of the artery supplying the territory of the infarct. The associated vascular lesions were as follows: segmental arterial disorganization 40 (with enlargement 31, with hemorrhage 26, with fibrinoid deposit 14), thrombosis of a fusiform asymmetric microaneurysm, 2; plaque of foam cells (atherosclerosis) 3; complete absence of any lesion 1; suspected segmental disorganization 3; and miscellaneous 1. Segmental arterial disorganization has been discussed in some detail. Others have termed this condition hyalinosis, angionecrosis with aneurysm formation, plasmatic destruction, fibrinoid necrosis, fibrinoid arteritis, etc.

High-energy electroproduction and the constitution of the electric current

Abstract: The asymptotic behavior of electroproduction cross sections is shown to contain information about the constitution of the electric current.

THE ULTRASTRUCTURE OF THE CAT MYOCARDIUM: I. Ventricular Papillary Muscle

Abstract: The ultrastructure of cat papillary muscle was studied with respect to the organization of the contractile material, the structure of the organelles, and the cell junctions. The morphological changes during prolonged work in vitro and some effects of fixation were assessed. The myofilaments are associated in a single coherent bundle extending throughout the fiber cross-section. The absence of discrete "myofibrils" in well preserved cardiac muscle is emphasized. The abundant mitochondria confined in clefts among the myofilaments often have slender prolongations, possibly related to changes in their number or their distribution as energy sources within the contractile mass. The large T tubules that penetrate ventricular cardiac muscle fibers at successive I bands are arranged in rows and are lined with a layer of protein-polysaccharide. Longitudinal connections between T tubules are common. The simple plexiform sarcoplasmic reticulum is continuous across the Z lines, and no circumferential "Z tubules" were identified. Specialized contacts between the reticulum and the sarcolemma are established on the T tubules and the cell periphery via subsarcolemmal saccules or cisterns. At cell junctions, a 20 A gap can be demonstrated between the apposed membranes in those areas commonly interpreted as sites of membrane fusion. In papillary muscles worked in vitro without added substrate, there is a marked depletion of both glycogen and lipid. No morphological evidence for preferential use of glycogen was found.

Method and theory in the study of avoidance.

Abstract: Two-factor theories of avoidance were conceived to explain responding in avoidance procedures that closely resemble the Pavlovian paradigm in superficial features, although differing in the fundamental contingency of reinforcement. Both typically involve an arbitrary conditioned stimulus and a trial-by-trial sequence of pairings between the conditioned and unconditioned stimuli. According to two-factor theory, the instrumental reinforcement of avoidance is based on the Pavlovian reinforcement of a drive state in the presence of the conditioned stimulus. It has been shown, however, that the presence of the conditioned stimulus is not necessary for the occurrence of avoidance responding. A procedure in which the sole effect of the avoidance response was a reduction in the average frequency of occurrence of an aversive electric shock proved to be fully adequate to maintain lever pressing in rats, thereby suggesting that not all avoidance requires two factors. Further experiments with various new procedures suggested that the conditioned stimulus may function as a discriminative stimulus for the avoidance response, rather than as a stimulus whose removal is inherently reinforcing, as two-factor theory requires. The conditioned reflex was to I. P. Pavlov (1928, pp. 59-60) the final answer to the problem of biological adaptation. As a mechanist, Pavlov sought a naturalistic explanation for everything an animal did, which had come to mean an explanation in terms of physical processes that could be isolated by the vivisectionist techniques of nineteenth-century physiology. But the behavior of many animals, for example, the dog, precluded any such simple machinery. Dogs clearly differed in what they did and seemed to know even though they might share virtually identical inheritances. The psyche of 1 Preparation of this paper, as well as the conduct of the previously unpublished experiments described herein, was supported by grants from the National Science Foundation to Harvard University. The author wishes to express thanks to P. N. Hineline for his generosity in allowing use of some of his as yet unpublished data and for help in formulating some of the notions here advanced. An early and much reduced version of this paper was presented at the 1966 meeting of the American Association for the Advancement of Science, Washington, D. C., as part of a symposium on Aversive Control. The author owes thanks to J. V. Brady for having organized the symposium and for inviting him to participate in it. To another of the participants, D. Anger, special thanks are owed for his vigorous and insightful criticisms of many of the author's theoretical ideas. the dog was, in other words, a sizable obstacle to the progress of a science of adapta

Theory of Electronic Transport in Disordered Binary Alloys: Coherent-Potential Approximation

Abstract: The coherent-potential approximation (CPA) for single-particle properties of electrons in a disordered alloy ${A}_{x}{B}_{1\ensuremath{-}x}$ (Soven and others) is extended to complex admittances. The one-electron Kubo formula is used. The CPA is viewed as a single-site decoupling of the averaged multiple-scattering expansion. It properly gives the exact formulas in the limits of weak scattering (Edwards) and of dilute alloys (Langer). For any $x$ and any random-potential strength, CPA satisfies a number of physical conditions, including energy and particle-number conservation. The CPA equations are exactly soluble for a single-band model with short-ranged random scatterers. The vertex corrections are related to the response of local densities to a given disturbance. For the electrical conductivity $\ensuremath{\sigma}$, they vanish. Variation of $\ensuremath{\sigma}$ with the randompotential strength is studied numerically. A low-mobility region appears well before the band splits. In the split-band limit, CPA yields a reasonable finite $\ensuremath{\sigma}$ in the host band, but it fails in the impurity band.