Showing papers by "Stony Brook University published in 1969"

Nonanalytic Behavior Above the Critical Point in a Random Ising Ferromagnet

Abstract: It is shown that in a class of randomly diluted Ising ferromagnets the magnetization fails to be an analytic function of the field $H$ at $H=0$ for a range of temperatures above that at which spontaneous magnetization first appears.

The impact of college on students

Abstract: In this landmark work, Kenneth Feldman and Theodore Newcomb review and synthesize the findings of more than 1,500 studies conducted over four decades on the subject. Writing in 1991, Ernest Pascarella and Patrick Terenzini maintained that The Impact of College on Students not only provided the first comprehensive conceptual map of generally uncharted terrain, but also generated a number of major hypotheses about how college influences students. They also noted that Feldman and Newcombe helped to stimulate a torrent of studies on the characteristics of collegiate institutions and how students change and benefit during and after their college years from college attendance. The Impact of College on Students is now a standard text in graduate courses as well as a standard and frequently cited reference for scholars, students, and administrators of higher education. Much of what we understand about the developmental influence of college is based on this work.

Hypothesis of Limiting Fragmentation in High-Energy Collisions

Abstract: A hypothesis of limiting fragmentation of the target and of the projectile in a high-energy lepton-hadron or hadron-hadron collision is defined Arguments are given for the hypothesis Comparisons with various models and concepts are made Further speculations are made, including the absence of pionization processes in high-energy collisions and the dependence of multiplicity on the momentum transfer Experiments are suggested

A token reinforcement program in a public school: a replication and systematic analysis.

Abstract: A base rate of disruptive behavior was obtained for seven children in a second-grade class of 21 children. Rules, Educational Structure, and Praising Appropriate Behavior while Ignoring Disruptive Behavior were introduced successively; none of these procedures consistently reduced disruptive behavior. However, a combination of Rules, Educational Structure, and Praise and Ignoring nearly eliminated disruptive behavior of one child. When the Token Reinforcement Program was introduced, the frequency of disruptive behavior declined in five of the six remaining children. Withdrawal of the Token Reinforcement Program increased disruptive behavior in these five children, and reinstatement of the Token Reinforcement Program reduced disruptive behavior in four of these five. Follow-up data indicated that the teacher was able to transfer control from the token and back-up reinforcers to the reinforcers existing within the educational setting, such as stars and occasional pieces of candy. Improvements in academic achievement during the year may have been related to the Token Program, and attendance records appeared to be enhanced during the Token phases. The Token Program was utilized only in the afternoon, and the data did not indicate any generalization of appropriate behavior from the afternoon to the morning.

Incompleteness of the Critical Exponent Description for Ferromagnetic Systems Containing Random Impurities

Abstract: We consider the magnetic properties and spin correlation functions of a two-dimensional Ising model with random impurities near the critical temperature and find that the usual parametrization provided by the exponents $\ensuremath{\gamma}$, $\ensuremath{\delta}$, and $\ensuremath{\eta}$ and the correlation length $\ensuremath{\xi}$ for $T\ensuremath{\gtrsim}{T}_{c}$ does not describe our results. Experimental implications of this breakdown of the critical exponent forms are discussed.

Light Scattering and Pseudospinodal Curves: The Isobutyric-Acid-Water System in the Critical Region

Abstract: Intensity and linewidth measurements of light scattered by the isobutyric acid in water system are reported for various equilibrium states in the critical neighborhood of the temperature-concentration diagram. By extrapolation of these data to zero scattering angle and then to (unrealized) states below the phase separation temperature one may determine a common "pseudospinodal curve" ${T}_{\mathrm{sp}}(X)$ described by ${T}_{\mathrm{c}}\ensuremath{-}{T}_{\mathrm{sp}}(X)\ensuremath{\sim}{|X\ensuremath{-}{X}_{\mathrm{c}}|}^{\frac{1}{{\ensuremath{\beta}}^{\ifmmode\dagger\else\textdagger\fi{}}}}$ where $X$ is the concentration, and we find ${\ensuremath{\beta}}^{\ifmmode\dagger\else\textdagger\fi{}}\ensuremath{\simeq}0.37\ifmmode\pm\else\textpm\fi{}0.04$. As expected on the grounds of the homogeneity hypotheses, the value of ${\ensuremath{\beta}}^{\ifmmode\dagger\else\textdagger\fi{}}$ is essentially the same as the previously observed value of the exponent $\ensuremath{\beta}$ for the coexistence curve. Empirical equations of the form $I_{C,0}^{}{}_{}{}^{\ensuremath{-}1}\ensuremath{\propto}{[T\ensuremath{-}{T}_{\mathrm{sp}}(X)]}^{\ensuremath{\gamma}}$ and $D\ensuremath{\propto}{[T\ensuremath{-}{T}_{\mathrm{sp}}(X)]}^{{\ensuremath{\gamma}}^{*}}$ are used to effect the extrapolations to determine ${T}_{\mathrm{sp}}(X)$. Here ${I}_{C,0}$ and $D$ are the extrapolated zero-angle scattering intensity and the diffusion coefficient, while $\ensuremath{\gamma}$ and ${\ensuremath{\gamma}}^{*}$ are corresponding critical exponents. We show theoretically, however, that a value ${\ensuremath{\beta}}^{\ifmmode\dagger\else\textdagger\fi{}}\ensuremath{ e}\frac{1}{2}$ is inconsistent with the general validity of these empirical formulas, which should thus be discarded as over-all representations of the variations of $D$ and ${I}_{C,0}$. A tentative test is made of a more general scaling equation for ${I}_{C,0}$ by a convenient plot. Moderate success is obtained. The measurements confirm the exponent values $\ensuremath{\gamma}=1.24\ifmmode\pm\else\textpm\fi{}0.03$ and ${\ensuremath{\gamma}}^{*}=0.67\ifmmode\pm\else\textpm\fi{}0.03$. The distinction between pseudospinodal curves, determined by extrapolation from stable thermodynamics states, and a true spinodal curve which (if it exists) can only be observed by measurements on metastable states, is emphasized.

Regulation of Branched-Chain Amino Acid Biosynthesis in Salmonella typhimurium: Isolation of Regulatory Mutants

Abstract: 5′,5′,5′-Trifluoro-dl-leucine inhibited the activity of α-isopropylmalate synthetase (the initial enzyme unique to leucine biosynthesis) as well as the growth of Salmonella typhimurium. Mutants of S. typhimurium resistant to the analogue were isolated and characterized. In most cases, they overproduced and excreted leucine or leucine, valine, and isoleucine as a result of an alteration in the regulation of branched-chain amino acid biosynthesis. Biochemical and genetic tests allowed the mutants to be grouped into three classes: I, a moderately large group (13%) which had high, constitutive leucine biosynthetic enzyme levels and mutant sites linked to the leucine operon (operator constitutive); II, a single mutant in which the mutant site was linked to the leucine operon and in which α-isopropylmalate synthetase was not inhibited by leucine (feedback negative); III, a majority type which had constitutive levels of leucine, valine, and isoleucine biosynthetic enzymes and mutant sites unlinked to the leucine operon. Mutants of class I provide important evidence for the concept of an operon organization of genes involved in leucine biosynthesis. The properties of class III mutants indicate that there is some element involved in regulation which is common to the three pathways.

Marijuana and the politics of reality.

Abstract: It is asserted that the marijuana controversy is primarily a political, rather than a scientific, debate. It is a struggle to establish moral hegemony. Stances toward marijuana use and legalization are largely a manifestation of prior basic underlying ideological commitments. Scientific truth or falsity seem to have little or no impact on the positions taken-although both sides will invoke scientific findings and in fact will actually believe them-and have been preselected to verify a position already taken. Widely used concepts such as "drug abuse" reflect the ideological character of the controversy.

Direct Observation of Stress-Induced Shifts in Contact Potentials

Abstract: The effect of stress on contact potential has been measured semiquantitatively in Al, Cu, Au, steel, and brass using a high-sensitivity version of the Kelvin method. The observed shifts are in all samples positive (i.e., the electric field outside the sample is more positive when pressure is applied) and the magnitude is a few microvolts per kg/${\mathrm{cm}}^{2}$ applied stress. Both sign and magnitude agree with the theories of Dessler, Michel, Rorschach, and Trammell, and of Herring, provided one assumes that gravitationally produced stress is equivalent to hydraulically produced stress.

Idempotent-Separating Extensions Of Inverse Semigroups

Abstract: Extensions of semigroups have been studied from two points of view; ideal extensions and Schreier extension. In this paper another type of extension is considered for the class of inverse semigroups. The main result (Theorem 2) is stated in the form of the classical treatment of Schreier extensions (see e.g.[7]). The motivation for the definition of idempotentseparating extension comes primarily from G. B. Preston's concept of a normal set of subsets of a semigroup [6]. The characterization of such extensions is applied to give another description of bisimple inverse ω-semigroups, which were first described by N. R. Reilly [8]. The main tool used in the proof of Theorem 2 is Preston's characterization of congruences on an inverse semigroup [5]. For the standard terminology used, the reader is referred to [1].