Showing papers by "California Institute of Technology published in 1979"

Trace ideals and their applications

Abstract: Preliminaries Calkin's theory of operator ideals and symmetrically normed ideals convergence theorems for $\mathcal J_P$ Trace, determinant, and Lidskii's theorem $f(x)g(-i abla)$ Fredholm theory Scattering with a trace condition Bound state problems Lots of inequalities Regularized determinants and renormalization in quantum field theory An introduction to the theory on a Banach space Borel transforms, the Krein spectral shift, and all that Spectral theory of rank one perturbations Localization in the Anderson model following Aizenman-Molchanov The Xi function Addenda Bibliography Index.

Hybridization of synthetic oligodeoxyribonucleotides to ΦX 174 DNA: the effect of single base pair mismatch

Abstract: Oligodeoxyribonucleotides complementary to the DNA of the wild type (wt) bacteriophage ΦX174 have been synthesized by the phosphotriester method. The ollgomers, 11, 14, and 17 bases long, are complementary to the region of the DNA which accounts for the am-3 point mutation. When hybridized to am-3 DNA, the oligonucleotides form duplexes with a single base pair mismatch. The thermal stability of the duplexes formed between wt and am-3 DNAs has been measured. The am-3 DNA: ollgomer duplexes dissociate at a temperature about 10°C lower than the corresponding wt DNA: ollgomer duplexes. This dramatic decrease in thermal stability due to a single mismatch makes it possible to eliminate the formation of the mismatched duplexes by the appropriate choice of hybridization temperature. These results are discussed with respect to the use of oligonucleotides as probes for the isolation of specific cloned DNA sequences.

The excitation of density waves at the Lindblad and corotation resonances by an external potential.

Abstract: We calculate the linear response of a differentially rotating two-dimensional gas disk to a rigidly rotating external potential. The main assumptions are that the sound speed is much smaller than the orbital velocity and that the external potential varies on the scale of the disk radius. We investigate disks both with and without self-gravity. The external potential exerts torques on the disk only at the Lindblad and corotation resonances. The torque is positive at the outer Lindblad resonance and negative at the inner Lindblad resonance; at corotation the torque has the sign of the radial gradient of vorticity per unit surface density. The torques are of the same order of magnitude at both types of resonance and are independent of the sound speed in the disk. The external potential also excites density waves in the vicinity of the Lindblad and corotation resonances. The long trailing wave is excited at a Lindblad resonance. It transports away from the resonance all of the angular momentum which is deposited there by the external torque. Short trailing waves are excited at the corotation resonance. The amplitudes of the excited waves are the same on both sides of the resonance and are small unless the disk is almost gravitationally unstable. No net angular momentum is transported away from the corotation region by the waves. Thus the angular momentum deposited there by the external torque accumulates in the gas. We briefly discuss the behavior of particle disks and prove that the external torques on particle disks are identical to those on gas disks.

Dynamical Role of Light Neutral Leptons in Cosmology

Abstract: Using the Vlasov equation, we show that massive galactic halos cannot be composed of stable neutral leptons of mass \ensuremath{\lesssim} 1 MeV. Since most of the mass in clusters of galaxies probably consists of stripped halos, we conclude that the "missing mass" in clusters does not consist of leptons of mass \ensuremath{\lesssim} 1 MeV (e.g., muon or electron neutrinos). Lee and Weinberg's hypothetical heavy leptons (mass \ensuremath{\lesssim} 1 GeV) are not ruled out by this argument.

The jupiter system through the eyes of voyager 1.

Abstract: The cameras aboard Voyager 1 have provided a closeup view of the Jupiter system, revealing heretofore unknown characteristics and phenomena associated with the planet's atmosphere and the surfaces of its five major satellites. On Jupiter itself, atmospheric motions-the interaction of cloud systems-display complex vorticity. On its dark side, lightning and auroras are observed. A ring was discovered surrounding Jupiter. The satellite surfaces display dramatic differences including extensive active volcanism on Io, complex tectonism on Ganymede and possibly Europa, and flattened remnants of enormous impact features on Callisto.

The application of model-referenced adaptive control to robotic manipulators

Abstract: The achievement of quality dynamic performance in manipulator systems is difficult using conventional control methods because of both the inherent geometric nonlinearities of these systems and the dependence of the system dynamics on the characteristics of manipulated objects. A model-referenced adaptive control law is developed for maintaining uniformly good performance over a wide range of motions and payloads. The effectiveness of the approach is demonstrated in several simulations and the system stability as a function of input is investigated. Also developed is a 'learning signal' approach designed to minimize initial transients arising from abrupt changes in the inertial payload.

Acoustic fluidization: A new geologic process?

Abstract: A number of geologic processes, particularly seismic faulting, impact crater slumping, and long runout landslides, require the failure of geologic materials under differential stresses much smaller than expected on the basis of conventional rock mechanics. This paper proposes that the low strengths apparent in these phenomena are due to a state of 'acoustic fluidization' induced by a transient strong acoustic wave field. The strain rates possible in such a field are evaluated, and it is shown that acoustically fluidized debris behaves as a newtonian fluid with a viscosity in the range 100,000 to 10,000,000 P for plausible conditions. Energy gains and losses in the acoustic field are discussed, and the mechanism is shown to be effective if internal dissipation in the field gives a Q approximately greater than 100. Whether such values for Q are realized is not known at present. However, acoustic fluidization provides a qualitatively correct description of the failure of rock debris under low differential stresses in the processes of faulting, crater slumping, and long runout landslides. Acoustic fluidization thus deserves serious consideration as a possible explanation of these phenomena.

Regulation of gene expression: possible role of repetitive sequences

Abstract: Large contrasts are observed between the messenger RNA populations of different tissues and of embryos at different stages of development. Nevertheless, coding sequences for genes not expressed in a cell appear to be present in its nuclear RNA. Though many nuclear RNA transcripts of single copy DNA sequences are held in common between tissues, an additional set, probably consisting of non-message sequences, is not shared. Nuclear RNA also contains transcripts of repetitive DNA sequences. Certain repeat families are represented at high levels in the nuclear RNA of particular tissues and much lower levels in others. It is surprising that both complements of most repeat sequences are present in nuclear RNA. These observations lead to model for regulation of gene expression in which the formation of repetitive RNA-RNA duplexes controls the production of messenger RNA.

Ionic basis of the receptor potential in a vertebrate hair cell.

Abstract: Vertebrate hair cells, the primary receptors of auditory, vestibular and lateral-line organs, occur in epithelia which separate fluids of differing ionic composition. The apical surfaces of hair cells, on which the mechanosensitive hair bundles are situated, face a high-K+ fluid (termed endolymph in the inner ear); the basolateral surfaces instead contact fluid (perilymph or a related substance) of a composition similar to that of other extracellular fluids1–3. The universal occurrence of high-K+ fluid on the apical surfaces of hair cells in vertebrates has been taken as evidence that it is important for the transduction process, in particular that it relates to the ionic specificity4 of the conductance change5 underlying the receptor potential. There is, however, conflicting experimental evidence regarding this specificity. K+ has generally been thought to carry the receptor current, as replacement of endolymph with perilymph in the guinea pig cochlea abolishes the extracellularly recorded microphonic potential6. Yet microphonic potentials, as well as intracellular receptor potentials, have been recorded in other preparations when the apical surfaces of the hair cells faced instead a high-Na+ saline, and thus when the electrochemical gradient for K+ was near zero5,7. Ca2+ has also been proposed to carry the receptor current8, but its concentration is quite low in endolymph3, particularly that of the mammalian cochlea9. We present evidence here that the receptor current in a vertebrate hair cell is carried in vivo by K+, but that the transduction channel is in fact nonspecific, being permeable to Li+, Na+, K+, Rb+, Cs+, Ca2+, and at least one small organic cation.

The galilean satellites and jupiter: voyager 2 imaging science results.

Abstract: Voyager 2, during its encounter with the Jupiter system, provided images that both complement and supplement in important ways the Voyager 1 images. While many changes have been observed in Jupiter's visual appearance, few, yet significant, changes have been detected in the principal atmospheric currents. Jupiter's ring system is strongly forward scattering at visual wavelengths and consists of a narrow annulus of highest particle density, within which is a broader region in which the density is lower. On Io, changes are observed in eruptive activity, plume structure, and surface albedo patterns. Europa's surface retains little or no record of intense meteorite bombardment, but does reveal a complex and, as yet, little-understood system of overlapping bright and dark linear features. Ganymede is found to have at least one unit of heavily cratered terrain on a surface that otherwise suggests widespread tectonism. Except for two large ringed basins, Callisto's entire surface is heavily cratered.

Compensation for channel dispersion by nonlinear optical phase conjugation.

Abstract: It is proposed that the process of nonlinear optical phase conjugation can be utilized to compensate for channel dispersion and hence to correct for temporal pulse broadening. Specifically, a four-wave nonlinear interaction is shown to achieve pulse renarrowing. Spectral bandwidth constraints of the input pulse are presented for typical phase-conjugate interaction parameters.

On electromagnetic waves in chiral media

Abstract: We analyze the propagation of electromagnetic waves through chiral media, i.e., through composite media consisting of macroscopic chiral objects randomly embedded in a dielectric. The peculiar effects that such media have on the polarization properties of the waves are placed in evidence. To demonstrate the physical basis of these effects, a specific example, chosen for its analytical simplicity, is worked out from first principles.

Some practical universal noiseless coding techniques

Abstract: Some practical adaptive techniques for the efficient noiseless coding of a broad class of such data sources are developed and analyzed. Algorithms are designed for coding discrete memoryless sources which have a known symbol probability ordering but unknown probability values. A general applicability of these algorithms to solving practical problems is obtained because most real data sources can be simply transformed into this form by appropriate preprocessing. These algorithms have exhibited performance only slightly above all entropy values when applied to real data with stationary characteristics over the measurement span. Performance considerably under a measured average data entropy may be observed when data characteristics are changing over the measurement span.

Viking relativity experiment - Verification of signal retardation by solar gravity

Abstract: Analysis of 14 months of data obtained from radio ranging to the Viking spacecraft verified, to an estimated accuracy of 0.1%, the prediction of the general theory of relativity that the round-trip times of light signals traveling between the earth and Mars are increased by the direct effect of solar gravity. The corresponding value for the metric parameter gamma is 1.000 plus or minus 0.002, where the quoted uncertainty, twice the formal standard deviation, allows for possible systematic errors.

Luminescent solar concentrators. 1: Theory of operation and techniques for performance evaluation.

Abstract: Techniques and calculations are presented that give explicit expressions for the over-all performance of a luminescent solar concentrator (LSC) in terms of the intrinsic spectral response and quantum efficiency of its constituents. We examine the single dye (or inorganic ion) LSC with emphasis on the planar geometry. Preliminary data on the degradation of candidate LSC dyes under severe weathering conditions are also given. Armed with our experimental results and analysis of solar absorption, self-absorption, and solar cell efficiency, we present a new genre of solar concentrator with a theory of operation for the device.

Restoration of visual cortical plasticity by local microperfusion of norepinephrine.

Abstract: Using a newly developed technique of continuous microperfusion, we obtained further evidence in support of our hypothesis that the neocortical catecholamines (CAs), particularly norepinephrine (NE), are responsible for a high level of cortical plasticity. We used the visual cortical changes in ocular dominance which follow a brief monocular deprivation as a simple and reliable index of cortical plasticity. Local perfusion of kitten visual cortex with 1 mg/ml (4.0 mM) 6-hydroxydopamine (6-OHDA) prevented the effects of monocular deprivation in kittens, thus replicating the results we had obtained using intraventricular injections (Kasamatsu and Pettigrew, '76b, '79). Locally perfused NE at a concentration of of 10(-2) mg/ml (48.6 micron) restored visual cortical plasticity in animals which were no longer susceptible to brief monocular lid-suture. These numbers refer to the concentration of solutions in the cannula/minipump system. The effective concentrations at the site of recording (about 2 mm away) are probably much lower than these. This effect of NE perfusion was seen both in kittens which had received prior 6-OHDA treatment as well as in older animals which had outgrown the susceptible period. In the kittens we obtained as a nearly complete shift in ocular dominance toward the open eye and in the older animals a decrease in binocularity was obtained. The changes were found only in the local region of visual cortex perfused with either NE or 6-OHDA, while nearby cortical regions in the same animals were unaffected. There were no obvious changes in receptive field properties of individual neurons other than ocularity, and externally perfused NE did not itself reduce binocularity in normal animals: the effects of NE described about only occurred when the animal's visual experience was simultaneously altered. These results support the view that NE plays an important role in cortical plasticity.

Mechanisms of sound localization in the barn owl (Tyto alba)

Abstract: 1. We investigated the mechanisms by which the barn owl (Tyto alba) determines the azimuth and elevation of a sound source. Our measure of localizing ability was the accuracy with which the owl oriented its head to a sound source. 2. When localizing tonal signals, the owl committed the smallest errors at frequencies between 4 and 8 kHz. The azimuthal component of these errors was frequency independent from 1 to 8 kHz, but the elevational component increased dramatically for frequencies below 4 kHz. 3. The owl's mean error when localizing wide band noise was nearly three times less than its mean error when localizing the optimal frequency for tonal localization (6 kHz). 4. Occluding the right ear caused the owl to orient below and to the left of the sound source; occluding the left ear caused it to orient above and to the right of the sound source. 5. With ruff feathers (facial ruff) removed, the owl continued to localize sounds accurately in azimuth, but failed to localize sounds in elevation. 6. We conclude from these results that the barn owl uses interaural comparisons of sound spectrum to determine the elevation of a sound source. Both interaural onset time and interaural spectrum are used to identify the azimuth of the sound source. If onset time is not available (as in a continuous sound), the owl can derive the azimuth of the source from interaural spectrum alone, but its spatial resolution is poorer.

The anthropic principle and the structure of the physical world

Abstract: The basic features of galaxies, stars, planets and the everyday world are essentially determined by a few microphysical constants and by the effects of gravitation. Many interrelations between different scales that at first sight seem surprising are straightforward consequences of simple physical arguments. But several aspects of our Universe—some of which seem to be prerequisites for the evolution of any form of life—depend rather delicately on apparent ‘coincidences’ among the physical constants.

Quantum number and energy scaling for nonreactive collisions

Abstract: Two new theoretical developments are presented in this article. First an energy corrected sudden (ECS) approximation is derived by explicitly incorporating both the internal energy level spacing and the finite collision duration into the sudden S‐matrix. An application of this ECS approximation to the calculation of rotationally inelastic cross sections is shown to yield accurate results for the H+–CN system. Second, a quantum number and energy scaling relationship for nonreactive S‐matrix elements is derived based on the ECS method. A few detailed illustrations are presented and scaling predictions are compared to exact results for R–T, V–T, and V–R, T processes in various atom–molecule systems. The agreement is uniformly very good — even when the sudden approximation is inaccurate. An important result occurs in the analysis of V–T processes: the effects of anharmonic wave functions (coupling) and decreasing vibrational energy gaps (energetics) are separated. Each factor makes significant contributions to the deviation of the anharmonic from the harmonic scaling relationship.

Preservation of binocularity after monocular deprivation in the striate cortex of kittens treated with 6-hydroxydopamine.

Abstract: The results of single unit recordings from Area 17 of monocularly deprived kittens were compared with similar ones from littermates who had been monocularly lid-sutured for the same period of time, but who had in addition been given intraventricular injections of 6-hydroxydopamine (6-OHDA) to deplete brain catecholamines. This visual cortices of all catecholamine-depleted kittens showed high proportions of binocular neurons, in contrast to the control group, a majority of whose visual cortical neurons were driven exclusively by the non-deprived eye. Preservation of binocularity in 6-OHDA-treated kittens was dose-related. Even after a 1 to 2-week period of lidsuture which reduced binocularity to 20% in controls, normal proportions of binocular neurons (greater than 75%) were preserved if the cumulative dose had been 10 mg 6-OHDA or more. The density of single neurons sampled from electrode tracks through the cortex of drug-treated kittens was high and did not differ significantly from controls. Neurons were isolated every 100 micron on the average. There was some indication that the drug's effect in preventing an ocular dominance shift disappears by six weeks following cessation of 6-OHDA treatment. This reversal of the physiological effects in cortex is preceded by recovery from the behavioral manifestations of 6-OHDA treatments. Binocularity was only slightly increased in a kitten who received large doses of 6-OHDA after a period of monocular deprivation. This observation, together with control recordings from normal kittens and adults treated with 6-OHDA, indicates that the direct effects of 6-OHDA on cortical neurons' response properties play a minor role in comparison to its effects in reducing the sensitivity of the cortex to monocular deprivation. The overwhelming majority of cortical neurons in 6-OHDA-treated kittens remained normal in receptive field properties after a period of monocular deprivation. These data support the hypothesis that catecholamines are required for the maintenance of visual cortical plasticity during the critical period.

High-Resolution X-Ray Photoelectron Spectroscopy as a Probe of Local Atomic Structure: Application to Amorphous Si O 2 and the Si-Si O 2 Interface

Abstract: The chemical structure of thin Si${\mathrm{O}}_{2}$ films and Si${\mathrm{O}}_{2}$-Si interfaces has been investigated using high-resolution x-ray photoelectron spectroscopy. The data are consistent with a continuous random network of four-, six-, seven-, and eight-member rings of Si${\mathrm{O}}_{4}$ tetrahedra joined together by bridging oxygens. This distribution changes substantially within 30 \AA{} of the Si${\mathrm{O}}_{2}$-Si interface. The near-interface region is comprised of ${\mathrm{Si}}_{2}$${\mathrm{O}}_{3}$, SiO, and ${\mathrm{Si}}_{2}$O. This structure is interpreted by means of a structure-induced-charge-transfer model.

Local atomic and electronic structure of oxide/GaAs and SiO2/Si interfaces using high-resolution XPS

Abstract: The chemical structures of thin SiO2 films, thin native oxides of GaAs (20-30 A), and the respective oxide-semiconductor interfaces, have been investigated using high-resolution X-ray photoelectron spectroscopy. Depth profiles of these structures have been obtained using argon ion bombardment and wet chemical etching techniques. The chemical destruction induced by the ion profiling method is shown by direct comparison of these methods for identical samples. Fourier transform data-reduction methods based on linear prediction with maximum entropy constraints are used to analyze the discrete structure in oxides and substrates. This discrete structure is interpreted by means of a structure-induced charge-transfer model.

Plasma Observations Near Uranus: Initial Results from Voyager 2

Abstract: Extensive measurements of low-energy positive ions and electrons in the vicinity of Uranus have revealed a fully developed magnetosphere. The magnetospheric plasma has a warm component with a temperature of 4 to 50 electron volts and a peak density of roughly 2 protons per cubic centimeter, and a hot component, with a temperature of a few kiloelectron volts and a peak density of roughly 0.1 proton per cubic centimeter. The warm component is observed both inside and outside of L = 5, whereas the hot component is excluded from the region inside of that L shell. Possible sources of the plasma in the magnetosphere are the extended hydrogen corona, the solar wind, and the ionosphere. The Uranian moons do not appear to be a significant plasma source. The boundary of the hot plasma component at L = 5 may be associated either with Miranda or with the inner limit of a deeply penetrating, solar wind-driven magnetospheric convection system. The Voyager 2 spacecraft repeatedly encountered the plasma sheet in the magnetotail at locations that are consistent with a geometric model for the plasma sheet similar to that at Earth.

The motion of a deformable drop in a second-order fluid

Abstract: The cross-stream migration of a deformable drop in a unidirectional shear flow of a second-order fluid is considered. Expressions for the particle velocity due to the separate effects of deformation and viscoelastic rheology are obtained. The direction and magnitude of migration are calculated for the particular cases of Poiseuille flow and simple shear flow and compared with experimental data.