Showing papers by "University of Maryland, College Park published in 1968"

Klein-Gordon Geon

Abstract: A study of the spherically symmetric eigenstates of the Klein-Gordon Einstein equations (Klein-Gordon geons) reveals that these geons have properties that are uniquely different from other gravitating systems that have been studied. The equilibrium states of these geons seem analogous to other gravitating systems; but when the question of stability is considered from a thermodynamical viewpoint, it is shown that, in contrast with other systems, adiabatic perturbations are forbidden. The reason is that the equations of state for the thermodynamical variables are not algebraic equations, but instead are differential equations. Consequently, the usual concept of an equation of state breaks down when Klein-Gordon geons are considered. When the question of stability is reconsidered in terms of infinitesimal perturbations of the basic fields, it is then found that Klein-Gordon geons will not undergo spherically symmetric gravitational collapse. Thus, Klein-Gordon geons are counterexamples to the conjecture that gravitational collapse is inevitable.

Gravitational Radiation in the Limit of High Frequency. I. The Linear Approximation and Geometrical Optics

Abstract: A formalism is developed for obtaining approximate gravitational wave solutions to the vacuum Einstein equations of general relativity in situations where the gravitational fields of interest are quite strong. To accomplish this we assume the wave to be of high frequency and expand the vacuum field equations in powers of the correspondingly small wavelength, getting an approximation scheme valid for all orders of $\frac{1}{r}$, for arbitrary velocities up to that of light, and for all intensities of the gravitational field. To lowest order in the wavelength, we obtain a gauge-invariant linearized equation for gravitational waves which is just a covariant generalization of that for massless spin-2 fields in a flat background space. This wave equation is solved in the WKB approximation to show that gravitational waves travel on null geodesics of the curved background geometry with their amplitude, frequency, and polarization modified by the curvature of space-time in exact analogy to light waves.

Gravitational radiation in the limit of high frequency. II - Nonlinear terms and the effective stress tensor.

Abstract: The high-frequency expansion of a vacuum gravitational field in powers of its small wavelength is continued. We go beyond the previously discussed linearization of the field equations to consider the lowest-order nonlinearities. These are shown to provide a natural, gauge-invariant, averaged stress tensor for the effective energy localized in the high-frequency gravitational waves. Under the assumption of the WKB form for the field, this stress tensor is found to have the same algebraic structure as that for an electromagnetic null field. A Poynting vector is used to investigate the flow of energy and momentum by gravitational waves, and it is seen that high-frequency waves propagate along null hypersurfaces and are not backscattered by the lowest-order nonlinearities. Expressions for the total energy and momentum carried by the field to flat null infinity are given in terms of coordinate-independent hypersurface integrals valid within regions of high field strength. The formalism is applied to the case of spherical gravitational waves where a news function is obtained and where the source is found to lose exactly the energy and momentum contained in the radiation field. Second-order terms in the metric are found to be finite and free of divergences of the $\frac{(\mathrm{ln}r)}{r}$ variety.

Improved Stark profile calculations for the hydrogen lines H alpha, H beta, H gamma, and H delta.

Abstract: The frequency distributions of the first four Balmer lines broadened by the local fields of both ions and electrons in a plasma are calculated in the classical path approximation. The electron collisions are treated by an impact theory accounting for upper- and lower-level perturbations and allowing (approximately) for level splittings caused by the ion fields, finite duration of the collisions, and screening of the electron fields. Ion effects are calculated in the quasistatic, linear Stark-effect approximation, using Hooper's distribution functions, which include correlation and shielding effects to high orders. Theoretical uncertainties (mainly from the impact approximation) generally increase with density, frequency separation from the line center, and decreasing temperature. However, they only exceed \ensuremath{\sim}10% when a substantial fraction of the electrons begins to act quasistatically, and agreement with measured linewidths is within 10% in all cases.

Quantum Spectroscopy of the Low-Field Oscillations in the Surface Impedance

Abstract: We present here a detailed theory of electronic surface quantum states in a low magnetic field, as well as of their effects on the microwave surface impedance. A marked oscillatory structure in the microwave absorption as a function of magnetic field has been carefully observed by Khaikin and by Koch et al. The quantized magnetic surface levels are bound states of electrons trapped against the surface by the magnetic field. Even though these levels are somewhat analogous to Landau levels, they have considerably different properties. Resonant transitions between these levels give rise to a series of spectral lines in the surface impedance, just as cyclotron resonance is a result of transitions between Landau levels. The present effect is essentially quantum in nature, however. A considerable amount of quantitative information can be extracted from the experimental data. The Fermi velocity, radius of curvature of the Fermi surface, and mean free time at certain points on the Fermi surface can be obtained. Most novel, however, is the fact that one can extract information on the scattering of electrons by the surface, as a function of impact angle.

Spectral properties of matrices which have invariant cones

Abstract: Matrix theorem giving necessary and sufficient conditions for leaving cone invariant, considering finite dimensional spaces

Anticipation and timing in human motor performance.

Abstract: Recent evidence concerning the role of anticipation and timing in human motor performance is reviewed Evidence generally indicates that anticipation and timing can be learned, and that there is substantial forgetting over retention intervals of up to 5 months The spatial and temporal predictability of the stimuli appear to be the most potent determiners of anticipation, but response-produced proprioceptive stimulus traces may also provide a basis for more accurate timing Changes in the nature of the stimulus predictability produce widely different response strategies, and after considerable practice, anticipated responses become automatic, freeing S to perform other tasks simultaneously There has been a general lack of interest concerning both "intraresponse" timing and the motor variables determining anticipation

Gravitational-Wave-Detector Events

Abstract: A new series of experiments is described, involving two gravitational wave detectors spaced about 2 km A number of coincident events have been observed, with extremely small probability that they are statistical It is clear that on rare occasions these instruments respond to a common external excitation which may be gravitational radiation

Motility in procaryotic organisms: problems, points of view, and perspectives.

Abstract: Summary 1. Procaryotic motility mechanisms are more difficult to investigate than those of the generally larger, hence more easily observable, eucaryotic forms. Furthermore, although the function—namely translational locomotion—is the same, the biomechanisms by which this end is accomplished may be, in fact, quite distinct in the two forms. 2. Observational techniques for studying procaryotic motility are relatively crude and qualitative. Progress toward a greater understanding of motility phenomena will be made correlative with advances derived from devising specific techniques involving approaches adapted from electrical engineering, biophysics and cybernetics. 3. There is a great amount of information at hand concerning the qualitative and quantitative chemical composition of procaryotic flagella, but there is no assurance that preparatory techniques include either the entire organelle on the one hand, or do not introduce subtle errors on the other hand. Similarly, the structural features of flagella as derived from electron-microscope studies of fixed preparations may be themselves influenced by the techniques employed to reveal them. 4. Chemotactic responses of bacteria have been noted almost since the beginning of bacteriology as a formal scientific endeavour, yet the study of transduction of environmental stimuli, using motile bacteria as experimental subjects, is a relatively recent development. We have proposed that the cytoplasmic membrane may act as a non-specific receptor-transmitter of such signals in motile bacteria. If this is found to be the case, perhaps a sensory code may be more amenable to discovery here than with more complex forms of organisms. 5. Knowledge of the physical aspects in procaryotic flagellar movement is extremely fragmentary. There is some information on the movements of living functional flagellar fascicles, but this form of movement of an individual flagellum is purely speculative. We have proposed that the procaryotic flagellum is a rigid or semi-rigid helix, which does not transmit helical waves of contraction, and that its movements are governed by a specialized area of the cytoplasmic membrane. The flagellum may rotate or wobble within the flagellar basal bulb to produce the motion necessary for propulsion. This view ‘explains’ many of the known properties of procaryotic flagella. 6. The basis of gliding motility remains unknown even after a great deal of experimental work. In our view, the secretion of slime is necessary for adhesion to a solid surface, and movement is believed to be mediated by a mechanism involving contractile waves. 7. Studies on procaryotic motility may yield valuable information on certain areas of general biological interest. Among these are: (a) the transduction of environmental stimuli and the sensory code; (b) the development of reproducible observational techniques for quantitative data on the hydrodynamic and biophysical parameters of cell motion in procaryotic forms; (c) the phenomenon of unicellular ‘behaviour’ and the survival value and evolutionary significance of motility; and (d) the elucidation of the mechanism of gliding with perhaps an assessment of its utility in a wide variety of micro-organisms. All of these areas are ripe for imaginative and innovative experimentation; let us hope it will be forthcoming!

Long-Range Forces from Neutrino-Pair Exchange

Abstract: The long-range forces arising from neutrino-pair exchange between elementary systems are studied with the use of dispersion-theoretic techniques previously applied to the study of multiphoton exchange. It is shown that the potential decreases as ${r}^{\ensuremath{-}5}$ for large separation $r$, independently of the particles or systems under consideration. The weak lepton-lepton force does not seem to be observable at present in laboratory experiments. The long-range forces on neutrinos are also studied. For the case of two neutral molecules, a numerical comparison is made of the three types of long-range forces: gravitational, electromagnetic, and weak.

Nonlinear oscillations in a cold plasma.

Abstract: Nonlinear large amplitude electrostatic and electromagnetic oscillations in cold plasma having one dimensional spatial variations and fixed neutralized ion background

On the validity of the kirkwood-riseman theory.

Abstract: The theory of transport processes in polymer solutions, including hydrodynamic interaction between segments of the polymer chain, has been developed extensively along lines originally indicated by Kirkwood and Riseman. 1 2 They applied the Oseen approximation3 4 to the \"pearl necklace\" model of a polymer. That approximation is equivalent to the assumption that each monomer is a point source of friction in the solvent. One of the steps in the calculation of the transport coefficients is the solution of a set of equations of the form

Musical Consonance as Musical Preference: A Cross-Cultural Study

Abstract: (1968). Musical Consonance as Musical Preference: A Cross-Cultural Study. The Journal of General Psychology: Vol. 79, No. 1, pp. 129-142.

Transition Probabilities in the Spectra of Ne i, Ar i, and Kr i*

Abstract: Theoretical transition probabilities and oscillator strengths are given for a number of infrared-transition arrays in Ne i and Ar i, and for the visible 5s–5p array in Kr i. About 100 Ne i gas-laser lines, and about 10 from Ar i, are included. Our calculations are based on the intermediate-coupling aproximation. Configurations were chosen for line-strength calculations on the basis of goodness of fit of observed energies and Lande g values to those calculated in intermediate coupling; of the many transition arrays possible we chose only the strongest arising from each configuration, as being least susceptible to the effects of configuration interaction. On the basis of comparisons with experimental results for other s–p transition arrays in these gases we estimate that the relative strengths of the strongest half of the lines in each array are correct to about 35%. The results for the p–d arrays are probably as good. The Coulomb approximation was used to obtain absolute line strengths; we estimate that the values of σ2 so obtained are correct to about 25%. The transition arrays treated were: Ne i 4s–3p, 4s–4p, 5s–4p, 5s–5p, 6s–5p, 6s–6p, 7s–6p, 7s–7p, 3p–3d, 4p–3d, 4p–4d, 5p–4d, 5p–5d, 6p–5d, 6p–6d, 7p–6d; Ar i 5s–4p, 5s–5p, 6s–5p, 6s–6p, 7s–6p; Kr i 5s–5p.

Motivation, Incentive Systems, and the Political Party Organization*

Abstract: Several different models of local political party organization can be found in the accumulating studies of American local politics. One model is typified by the research of Forthal, Gosnell, Kent, and Salter, and presents a picture of the party organization as attracting and disciplining workers through material incentives, non-ideological in its appeals, and oriented toward obtaining votes for securing or maintaining the party in political control of the government. An alternative model has been described in more recent research by Wilson, Hirschfield, and Carney. They portray the party activist as being more ideologically oriented, responding to ideological rather than material incentives, and seeking governmental reform or improved governmental services. Changes in the environment have been identified as the causal forces for this change in political party organizational style. For example, Greenstein points out that urban party machines developed to provide required services for which demand was generated by rapid urbanization, disorganized governmental structures, and the needs of recent immigrants. The research describing the material-incentive-motivated political machines was produced primarily during the 1920's and 1930's when the need for accommodation to urban problems of the type described existed to a greater degree than at present.The social characteristics of the activists as well as the political style of the two types of party organizations described in the professional and amateur models also differ. The professional model presents a party organization whose members are male, oriented toward material rewards or a career in government, and exhibit little concern for issues.