Explicit Restrictions Research Articles

TIC: A timed calculus

Abstract TIC is a timed algebraic calculus which combines ideas from asynchronous and synchronous calculi. Time is introduced by assigning explicit time restrictions to the events of an asynchronous calculus. The semantics is defined in an operational way. Interleaving of behaviours is defined in such a way that a proper merge of events in time is achieved. Weak timed bisimulation is also defined. Examples are presented to show the applicability of the calculus to the study of timed behaviours.

Growth controls: policy analysis for the second generation

The 1970s spawned a ‘first generation’ of growth controls which featured explicit (or implicit) restrictions on residential housing construction. These restrictions were typically implemented in small, affluent, and predominantly white suburban communities. Policy analysis responded by focusing almost singlemindedly on how such supply-side restrictions might increase housing prices and drive out the poor. The 1980s and 1990s have, however, given birth to a more comprehensive ‘second generation’ of controls which many major cities and metropolitan areas are considering. This generation ties commercial and industrial as well as residential development to the reduction of the negative externalities and congestion costs associated with growth. To fully evaluate this second generation, policy analysis must take into account not only housing price effects and the rate of job creation but also the full range of ‘amenity effects’ associated with differing rates of growth and attendant levels of traffic congestion, air pollution, and other ‘public bads.’ We develop a framework for such ‘second generation’ growth control analysis using San Diego as an example.

A Canadian case study report: Towards self‐managed automation in small offices

Abstract This report discusses a variety of policies in Canada, both at the federal level and in the province of Ontario, that relate to technological change. It finds that the emphasis has been on the development of new technologies, rather than on their implementation. The industrial sector has been the main focus, with almost no attention specifically towards office automation. An open market philosophy prevails, with few explicit restrictions on the managerial deployment of technical and human resources. The report is principally devoted to an analysis of the introduction of microcomputers for administrative work in academic department offices and the description of a demonstration project which addressed some of the problems which emerged. It describes a union‐initiated attempt to show how workers can manage the introduction of personal computers into their offices. The Self‐Managed Office Automation Project provided a resource centre, knowledgeable experts, training sessions, library materials, tech...

On constitutive inequalities and bifurcation in elastic-plastic solids with a yield-surface vertex

A constitutive inequality for time-independent elastic-plastic models of polycrystalline metals at finite strain is derived from the known constitutive framework for single metal crystals obeying the normality and symmetry postulates. Consequences of the inequality are examined for a general class of nonlinear constitutive rate equations at a yield-surface vertex. It is demonstrated that existence of a strain-rate potential and the normality flow rule can be inferred from the inequality alone. With the help of the constitutive inequality, it is proved that bifurcation in velocities is ruled out by positive definiteness of the quadratic functional based on the tangent moduli. Micromechanically-based justification for linearization of the bifurcation problem along a regular deformation path is obtained in that way, without the need of specifying the full constitutive law. As another example of application of the constitutive inequality, explicit restrictions on phenomenological models of material behaviour at a yield-surface vertex are derived.

Learning in artificial neural systems

This paper presents an overview and analysis of teaming in artificial neural systems (ANSs). It begins with a general introduction to neural networks and connectionist approaches to information processing. The basis for learning in ANSs is then described and compared with classical machine learning. While similar in some ways, ANS learning deviates from tradition in its dependence on the modification of individual weights to bring about changes in a knowledge representation distributed across connections in a network. This unique form of learning is analyzed from two aspects: the selection of an appropriate network architecture for representing the problem, and the choice of a suitable learning rule capable of reproducing the desired function within the given network. The various network architectures are classified, and then identified with explicit restrictions on the types of functions they are capable of representing. The learning rules, i.e., algorithms that specify how the network weights are modified, are similarly taxonomized and, where possible, the limitations inherent to specific classes of rules are outlined.

Restrictions on dynamically propagating surfaces of strong discontinuity in elastic-plastic solids

F or dynamic three-dimensional deformations of elastic-plastic materials, we elicit conditions necessary for the existence of propagating surfaces of strong discontinuity (across which components of stress, strain or material velocity jump). This is accomplished within a small-displacement-gradient formulation of standard weak continuum-mechanical assumptions of momentum conservation and geometrical compatibility, and skeletal constitutive assumptions which permit very general elastic and plastic anisotropy including yield surface vertices and anisotropic hardening. In addition to deriving very explicit restrictions on propagating strong discontinuities in general deformations, we prove that for anti-plane strain and incompressible plane strain deformations, such strong discontinuities can exist only at elastic wave speeds in generally anisotropic elastic-ideally plastic materials unless a material's yield locus in stress space contains a linear segment. The results derived seem essential for correct and complete construction of solutions to dynamic elastic-plastic boundary-value problems.

The Stability of a Dynamic Model of Traffic Assignment—An Application of a Method of Lyapunov

This paper considers a dynamic model of traffic assignment in which drivers change their route choices to take advantage of cheaper routes. Using a method due to Lyapunov, we show that if the cost-flow function is monotone and there are no explicit capacity restrictions then any solution trajectory of our dynamical system converges to the set of Wardrop equilibria as time passes.

Self-tuning regulators with explicit variance restrictions

Self-tuning regulators with on-line adaptation of the weights in a quadratic loss function are considered. The criterion for control is to minimize the variances of one or several process variables. Design constraints are taken into account by introducing explicit state and input variance restrictions. The algorithm solves the necessary optimality conditions of the variance-constrained optimal control problem using a stochastic approximation method. A particularly simple algorithm is obtained if the control is based on a single-step loss function. An example taken from multivariate cement kiln control shows, however, that there are practical situations when it is necessary to use a more complex algorithm, which requires the on-line solution of a Riccati equation.

Generalized Wald Methods for Testing Nonlinear Implicit and Overidentifying Restrictions

The W- ld approach to testing direct explicit restrictions on a parameter vector is generalizetd to the case of nonlinear implicit constraints. When applied to subsystems of simultaneous equations models, the generalization enables the symmetric joinit testing of nonlinear overidentufying structural restrictions under very wide cornditions. By varying the choices of certain matrices used to construct the generalized Wald statistic, one produces a whole class of tests which have equal asymptotic power yet whose associated structural coefficient estim,-iators have different asymptotic efficiencies for any given rediuced-form estimator from which they are derived. restrictions on a parameter vector was originally formulated in terms of the unrestricted maximum-likelihood estimator of that vector. Stroud [13] showed clearly how Wald criteria can be defined in terms of consistent asymptotically normal estimators other than maximum likelihood. While this makes the Wald

Shearfree congruences of null geodesies and killing tensors

In this communication, the mutual connections between quantities that are generalizations of the notion of a Killing vector field are investigated. A classification of these quantities in terms of a complex vector fieldαa is given. A common feature of all these quantities is that they imply the existence of a pair of shearfree geodetic null congruences. There are no explicit restrictions posed on the Ricci tensor.

ALTERNATIVE FORMS OF PROTECTION AGAINST MARKET DISRUPTION

SUMMARYVoluntary export restraints (VRSs) and orderly marketing arrangements (OMAs) are increasingly important relative to explicit trade restrictions such as tariffs and quotas. Unlike the latter, which are applied by the importing countries, VERs and OMAs as protectionist techniques are implemented under duress by the exporting nations themselves. They are part of a growing ‘rifle approach’ to protection designed to curb imports specifically from ‘disruptive’ supplier countries. Textiles, footwear, consumer electronics and steel are some of the product groups affected in recent years, with Japan, South Korea, Hong Kong, Brazil, Taiwan and Singapore among the main victims. In 1976 an estimated $ 9.4 billion of international trade was covered by such restrictions, or about 16% of OECD imports in the affected product categories. It is often alleged that such ‘voluntary’ controls are less trade‐restrictive than outright quotas imposed on imports. This paper shows that, in the event that export licences are themselves tradeable and subject to monopolization ‐ which is often the case – precisely the opposite will tend to be the case. Even greater restrictiveness may occur when multiple products are covered by a single OMA or VER.

To Love, Honor, and Obey? Traditional Legal Marriage and Alternative Family Forms

The law imposes an unwritten marriage contract on all men and women who enter legal marriage. This traditional marriage contract recognizes the husband as head of the family, holds the husband responsible for support, and holds the wife responsible for domestic and child care services. These legal obligations of spouses are examined in the first half of this article. The law's narrow and limited conception of a family and its imposition of legal responsibilities on the basis of sex serves to constrain alternative family forms. The second half of the article examines explicit legal restrictions on alternative family forms-homosexual unions, communes, and egalitarian-partnership marriages. The final section reviews recent developments in the law which may provide increased legal protection for alternative families.

SELFADJOINTNESS CONDITIONS FOR STRONGLY ELLIPTIC SYSTEMS OF ARBITRARY ORDER

Sufficient conditions are obtained for the essential selfadjointness in L2(R2) of strongly elliptic systems of arbitrary even order (both semibounded and nonsemibounded) without assumptions concerning the boundedness of the leading coefficients or concerning uniform ellipticity. The conditions are formulated by means of operator inequalities and explicit restrictions on the coefficients. Bibliography: 27 items.

Elastic-plastic continua with simple force dipole

This paper is concerned with a nonlinear theory of elastic-plastic continua in the presence of simple force and stress dipoles. General constitutive equations for such continua are developed and explicit restrictions are derived from thermodynamics. Infinitesimal theory is discussed as a special case and is applied to the example of torsion of an elastic-plastic, isotropic, circular cylinder.

A class of viscoelastic-plastic media

A class of nonlinear constitutive equations of rate-type are considered for viscoelastic-plastic continua and explicit restrictions are derived from thermodynamics. Some aspects of the associated linearized theory with isothermal deformations are also discussed.

XVII.—Generalized Hypo-Elasticity

SynopsisThe theory of Hypo-Elasticity is generalized so as to include the theory of (anisotropic) elasticity as a special case, and to include thermal effects. Explicit restrictions on the constitutive equations, arising from thermodynamics, are obtained.

A restricted random series of numbers

When using a random number table, it is often necessary to arbitrarily select a “random appearing” or non-predictable group from the series. To facilitate the construction of suitable groups, two sets of two digit numbers, 00 to 99, are presented which have explicit restrictions on the frequency and sequence of the digits.

Approximate Solution to the MultichannelND−1Equations

By making a pole approximation to the spectral integral over the kinematical factor ${\ensuremath{\rho}}_{l}(z)$ it is shown that the partial-wave matrix $N{D}^{\ensuremath{-}1}$ integral equations are reduced to algebra. The approximation depends only on the particular partial wave and not the dynamics of the reaction, and it admits of systematic improvement. The resulting scattering amplitude ${T}_{l}(z)$ is symmetric, is independent of the subtraction point for the $D$ function, has the correct discontinuities on the right- and left-hand cuts, and can moreover be explicitly expressed as an algebraic function of the driving term ${B}_{l}(z)$. This last feature enables us to directly inspect the relation between the driving force and the scattering amplitude, and establishes the general usefulness of the method. We find, for example, that the solution imposes general conditions on ${B}_{l}(z)$ for the existence of bound states, resonances, or possible ghosts. The self-consistency property of bootstrap calculations imposes additional explicit restrictions on acceptable ${B}_{l}(z)$ for the existence of the bootstrap.

A comment on drucker's postulate in the theory of plasticity

A general theory of an elastic-plastic continuum, valid for nonisothermal deformations and accompanied by explicit thermodynamical restrictions, was developed recently byGreen andNaghdi. A special case of this theory, assuming isothermal conditions, leads to constitutive relations which are equivalent to those which can be derived fromDrucker's postulate. Here, we discuss further the implication ofDrucker's postulate in connection with a set of constitutive equations for an elastic-plastic continuum in which the postulate need not be satisfied.

Plasticity theory and multipolar continuum mechanics

A general theory of an elastic-plastic continuum which is valid for non-isothermal deformation and which includes explicit restrictions derived from thermodynamics has been given recently by Green and Naghdi [2]. In the development of this theory, the analysis was carried out for a symmetric plastic strain tensor, although it was noted that it is possible to use instead a plastic strain tensor which is nonsymmetric and this would require only a slight modification of the results.