Causal Considerations Research Articles

Completeness of scattering states for rough interfaces: David H. Berman. Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa 52242

Abstract Using energy conservation and causality considerations, the completeness of scattering states is established for plane waves impinging on an irregular interface. Provided certain limiting operations commute with differentiation, it is shown that surface waves need not be explicity included in the Weyl representation of the Green's function in the presence of a rough interface. Rather, surface waves are implicity included through the poles of the scattering amplitudes. This result was used implicitly in a recently developed scheme to treat scattering in a duct using half-space scattering amplitudes (Berman, J. Acoust. Soc. Am. 92 (1992), 309–314).

How efficient is the Langacker-Pi mechanism of monopole annihilation?

We investigate the dynamics of monopole annihilation by the Langacker-Pi mechanism. We find taht considerations of causality, flux-tube energetics and the friction from Aharonov-Bohm scatteering suggest that the monopole annihilation is most efficient if electromagnetism is spontaneously broken at the lowest temperature ($T_{em} \approx 10^6 GeV$) consistent with not having the monopoles dominate the energy density of the universe.

The quest for optimality: A positive heuristic of science?

AbstractThis paper examines the strengths and weaknesses of one of science's most pervasive and flexible metaprinciples;optimalityis used to explain utility maximization in economics, least effort principles in physics, entropy in chemistry, and survival of the fittest in biology. Fermat's principle of least time involves both teleological and causal considerations, two distinct modes of explanation resting on poorly understood psychological primitives. The rationality heuristic in economics provides an example from social science of the potential biases arising from the extreme flexibility of optimality considerations, including selective search for confirming vidence, ex post rationalization, and the confusion of prediction with explanation. Commentators are asked to reflect on the extent to which optimality is (1) an organizing principle of nature, (2) a set of relatively unconnected techniques of science, (3) a normative principle for rational choice and social organization, (4) a metaphysical way of looking at the world, or (5) something else still.

Inversion of Apparent Attenuation and Phase Velocity to Determine Scattering Parameters

Summary We invert apparent attenuation in order to determine the scattering power spectrum. Examples are given illustrating this general inversion procedure including Wu's (1982) single-scattering theory for acoustic waves, and Lerche & Petroy's (1987) mean-field scattering model of both compressive and shear-waves by fluid-filled fractures. Frequency dependent phase velocity and attenuation factors for both compressive and shear-waves provide improvements in the inverse methods for separating intrinsic and apparent attenuation factors. In the cases where only total attenuation factors (phase velocities) are available, phase velocities (attenuation factors) can be determined by using causality considerations. For a small degree of attenuation per unit wavelength travelled approximate solutions provide relatively simple expressions connecting phase velocity and attenuation. If both phase velocity and apparent attenuation factors are measured for compressive and/or shear-waves, then the Kramers-Kronig causality relations provide consistency requirements which must be met. the non-linear nature of these causal requirements is used to explore an inverse method for separating intrinsic and apparent attenuation factors. the non-linear connections of (1) total attenuation to wave phase speeds, and (2) apparent attenuation to intrinsic attenuation, can be used to determine intrinsic properties of the propagation characteristic of the medium.

Parasuicide among Indian Adolescents: Some Cultural Perspectives

From the significant amount of research devoted to parasuicide it is evident that parasuicidal adolescents experience many unique problems. There is however a paucity of research in this regard on South African Indian patients. Culturally oriented research is necessary in order to gain a better understanding of the problems facing these patients, and for appropriate management and ultimate prevention of parasuicide. Accordingly a preliminary study of parasuicide among Indian adolescents was undertaken. The patients ( N = 54) were mostly older adolescent females who engaged in self-poisoning by overdose of medicinal substances. Culturally rooted authoritarian parenting and the effects of acculturation emerged as important causal considerations and are discussed in relation to the aetiology of parasuicidal behaviour in this group of patients.

Explanation of parity nonconservation

Space inversion and other discrete symmetries are treated within the frame of a theory of fundamental forces based only on general considerations of causality, symmetry, and stability, without ad hoc differential equations. The basic space-time M is the Einstein universe R(1) x S(3) as a causal (or conformal) rather than a pseudo-Riemannian manifold. Its connected symmetry group is then a 15-parameter group G locally equivalent to SO(2, 4), while the isometry group K of the Einstein universe is a 7-parameter subgroup. Correlation with conventional relativistic theory is based on a canonical imbedding of Minkowski space M(0) into M, together with the unique extendability of all transformations of the scaling-extended Poincaré group P from M(0) to global transformations on M. The fundamental fermion field F and boson field B are here restricted to be real and are fully invariant under G(e), where the superscript e denotes the inclusion of space and time inversions. The role of C on F is taken over by a real matrix having the eigenvalues +/-i, that commutes with G but anticommutes with space inversion. The spin space for B consists of the real linear transformations on that for F. There is a corresponding natural total Lagrangian that is both G(e) and O(2)-gauge invariant, the latter leading to lepton and baryon number conservation, and which is nonparametric except for scale. The Weyl and Maxwell equations are deduced, and compelling identifications made for neutrinos and the photon. The e and mu neutrino pairs occur in strikingly inequivalent positions in F, appearing symmetric only in the conventional relativistic limit R --> infinity, where R is the ( G-invariant) fundamental length interpretable as the radius of the space S(3). The photon occurs as the lowest member of a coherent subfamily of B that includes natural candidates for bare versions of the W and Z particles. In the relativistic limit the interaction Lagrangian becomes a sum over all elementary processes, one of which appears as quantum electrodynamics with Majorana-type electrons.

Juvenile Delinquency in China

It is clear that juvenile delinquency is now recognized as an important social issue within the People's Republic of China. The documents in this volume chronicle widely shared views concerning causal factors and treatment considerations from a variety of perspectives, only some of which are strictly educational. Indeed, the family, work unit, relevant public security organs as well as the school all have been delegated some responsibility for the prevention of juvenile delinquency. This being the case, it can be argued that the information presented here is illustrative of the strengths and weaknesses of a growing literature with a social science orientation, which addresses itself to the articulation and eventual solution of problems of youth in a general sense.

Representation and Explanation

Functionalism faces a problem in accounting for the semantic powers of beliefs and other mental states. Simple causal considerations will not solve this problem, nor will any appeal to the social utility of semantic interpretations. The correct analysis of semantic representation is a teleological one, in terms of the biological purposes of mental states: whereas functionalism focuses, so to speak, only on the structure of the cognitive mechanism, the semantic perspective requires in addition that we consider the purposes of the cognitive mechanism's parts.

Density fluctuations and particle-antiparticle annihilation

With the example of the primordial magnetic monopoles in mind, the time development of a system of particles and antiparticles undergoing irreversible annihilation is studied. The existence of spatial fluctuations in the initial particle and antiparticle densities is shown to lead to constraints on the asymptotic annihilation rate; the most general of these is based on causality considerations. The application of these constraints to several different types of systems is discussed, and computer simulations which were performed in order to test the constraints are described.

Dominance: The baby and the bathwater

AbstractThe concept of dominance is used in the behavioral and biological sciences to describe outcomes in a variety of competitive interactions. In some taxa, a history of agonistic encounters among individuals modifies the course of future agonistic encounters such that the existence of a certain type of relationship can be inferred. If one is to characterize such relationships as dominance, however, then they must be distinguished from other kinds of interaction patterns for which the term tends to be used, as well as from factors such as territoriality and "trained" winners and losers, which may also influence the expression of agonistic behavior. Operational definitions based on causal, functional, evolutionary, and ontogenetic considerations have been proposed. Reliability and validity problems have been discussed, but the dominance concept has proved useful despite methodological difficulties. The confusion of dominance relationships (which involve two or more individuals) with dominance ranks (which are assigned to a single individual) has obscured the possible evolutionary basis of dominance relationships. If benefits accrue to dominant members of pairs, then those attributes which allow an animal to establish dominance can be selected. Dominance per se and dominance ranks, on the other hand, cannot be genetically transmitted since they constitute relationships with other individuals rather than absolute attributes. Dominance rankings in particular may be useful for describing behavioral patterns within a group, but they may reflect our own ability to count rather than any important variable in social organization.

Energy Cost of Information Transfer

From thermodynamic and causality considerations a general upper bound on the rate at which information can be transferred in terms of the message energy is inferred. This bound is consistent with Shannon's bounds for a band-limited channel. It prescribes the minimum energy cost for information transferred over a given time interval. As an application, a fundamental upper bound of ${10}^{15}$ operations/sec on the speed of an ideal digital computer is established.

On: “A technique for the continuous representation of dispersion in seismic data” by J. C. Robinson (GEOPHYSICS, August 1979, p. 1345–1351).

Robinson’s paper concerns a topic of discussion in which geophysicists often find interest in attempting to describe the effect of the propagating medium on pulse wave shape and subsequently removing anelastic distortion. The present theory of linear anelastic wave propagation associates a dispersive mechanism and an absorptive mechanism with the change in pulse shape during propagation (Futterman, 1962; Ginzburg, 1955). In deference to causal considerations, these two mechanisms have been related to one another through the approximation of the Kramers‐Kronig relation.

Frequency-dependent feedback control of plasma instabilities

A general theory of simultaneous feedback stabilization of multimode oscillations in collisionless magnetized plasma is developed for reactive and dissipative instabilities. The gain and phase requirements of the feedback circuit are obtained using familiar stabilization techniques. From causality and stability considerations further requirements on phase and gain are determined for a physically realizable feedback system. It is shown that unstable modes can be suppressed without driving new instabilities or causing stable modes to become unstable. Although this method of stabilization provides marginal stability for instabilities of the reactive type by correctly choosing the frequency dependence of the feedback gain, this problem can be overcome, and the stability properties of the feedback loop can be improved. Applications to some known reactive instabilities are included as examples.

Observational validation of the chronometric cosmology: I. Preliminaries and the redshift-magnitude relation

Results of comprehensive observational tests of the cosmological theory proposed by Segal in 1972 are summarized in this and succeeding notes. Within a framework of natural and general causality and symmetry considerations, the theory is mathematically essentially unique. It implies definite relations between directly observed quantities (redshift, apparent magnitude and diameter, number counts, and the like) which are entirely free of adjustable parameters, such as the q(0) and Lambda of general relativistic cosmologies. Rigorous statistical analysis of large ( greater, similar100) or systematically defined samples of galaxies or quasars accepts these relations at substantial probability levels. Note I establishes uniform statistical procedures and compares the redshift-magnitude relations of major samples with the theoretical relations of the present and expansion theories.

Spectral Forms for Three-Point Functions

Single- and double-spectral forms for three-point functions are studied, in a detailed manner, within the framework of source theory. The methods developed, which are applicable beyond the present problem, are based on causal considerations and appear to provide some simplifications and advances over the conventional analytic methods. The spectral variables are any one or two of the momentum scalar products (${{p}_{\ensuremath{\alpha}}}^{2}, {{p}_{\ensuremath{\beta}}}^{2}, {{p}_{\ensuremath{\gamma}}}^{2}$) on which the three-point function depends, ${{p}_{\ensuremath{\alpha}}}^{2}$ and ${{p}_{\ensuremath{\alpha}}}^{2}\ensuremath{-}{{p}_{\ensuremath{\gamma}}}^{2}$, to be specific. After studying the lowest-order nontrivial contributions, a source-theoretic calculational scheme for contributions of arbitrary order is qualitatively developed, and it is used in establishing the spectral forms for general order. In lowest order the spectral weight functions are explicitly given, while in general order the main concern is the existence of the spectral forms. The spectral forms considered here are only ones with normal thresholds, and the methods give regions of those variables not in spectral form (${{p}_{\ensuremath{\beta}}}^{2}\ensuremath{-}{{p}_{\ensuremath{\gamma}}}^{2}$ and ${{p}_{\ensuremath{\beta}}}^{2}$) for which such spectral forms of general order occur, with all particles being allowed different masses. For the single-spectral studies the region is in agreement with that obtained conventionally. The region for the double-spectral form is all spacelike values of ${{p}_{\ensuremath{\beta}}}^{2}$; double-spectral forms for three-point functions of general order do not appear to have been investigated previously.

High-Energy Maxima in theπ−pCross Sections

It is pointed out that the consideration of causality requires that any description of the maximum in the ${\ensuremath{\pi}}^{\ensuremath{-}}\ensuremath{-}p$ total cross section at 800-Mev ${\ensuremath{\pi}}^{\ensuremath{-}}$ energy, and the maximum in the ${\ensuremath{\pi}}^{+}\ensuremath{-}p$ cross section at 1200-Mev, is necessarily equivalent to a description in terms of resonances and hence in terms of nucleon isobars.

TRENDS IN MAMMALIAN TERATOLOGY

It Might be worth while to begin a discussion of this topic with some historical considerations, because it may help to elucidate and to evaluate modern trends of mammalian teratology. It is probably true for all disciplines of science, but particularly so in the case of mammalian teratology, that the influence of the cultural environment of the time plays a decisive role in determining the attitude towards a particular science and its trends. It is obvious that teratologic phenomena are among those events of nature which fascinate and stimulate the imagination, not only of the scientist directly concerned with the problem, but also of the layman who happens to come across monstrosities of one or the other kind. Everybody knows of the role monsters played in Greek mythology. Descriptions of congenital abnormalities may be found in pre-Aristotelian times but it was Aristotle who made a first attempt at causal analysis, and thus introduced the scientific approach to problems of teratology. It is interesting to consider the argument with which he refuted the possible existence of monsters-which were thought to be part man, part animal: Aristotle was correct in denying the existence of such chimaerae but he was not correct in the choice of his argument which stated that different organisms could not develop together because of different gestation times. Modern trends of thought would lead us to argue against the existence of this type of monstrosity in terms of genetic differences. The generally static and dogmatic trend of the Middle Ages is reflected in the absence of any causal considerations of teratology during that time.

Some Protein Properties of Plant Protoplasm

ABSTRACT In attempting to explain the reactions and behaviour of living organisms, the experimental biologist is often tempted to fall back on the causal consideration of the observed phenomena in terms of the single living cell. While it is true that our physiological knowledge of this unit is almost negligible, there is at any rate a widely accepted belief that its properties may often be expressed in terms of two of its most important chemically active substances, the various proteins and their derivatives or the fatty bodies. So far as proteins are concerned, this assumption is justified by the classical analyses of Reinke and Rodewald,12’ which show that in the plasmodium of Fuligo varians, about 60 per cent, of the dry weight of protoplasm is composed of protein. It is therefore legitimate to consider the hypothesis that certain properties of normal plant cells appear to be most simply expressed in terms of their protein reactions.