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P L Knight

Publications and source records attributed to P L Knight.

12 recordsLinked to original sources
PubMed2002

Role of the intramolecular phase in high-harmonic generation.

We study numerically the generation of high-order harmonics by two-center molecules for arbitrary angles between the molecular axis and the laser polarization axis. For fixed angle, the harmonic spectrum exhibits a minimum at a frequency which is independent of the laser parameters. The amplitude of each harmonic is strongly angle dependent, and a pronounced minimum is found at the same angle where a sudden jump in the harmonic phase occurs. By calculating the spatial dependence of the harmonic amplitudes and phases, we are able to explain these effects in terms of interfering contributions from various regions within the molecule.

Journal Article↗
PubMed2001

Subsystem purity as an enforcer of entanglement.

We show that entanglement can always arise in the interaction of an arbitrarily large system in any mixed state with a single qubit in a pure state. This small initial purity is enough to enforce entanglement even when the total entropy is close to maximum. We demonstrate this feature using the Jaynes-Cummings interaction of a two-level atom in a pure state with a field in a thermal state at an arbitrarily high temperature. We find the time and temperature variation of a lower bound on the amount of entanglement produced and study the classical correlations quantified by the mutual information.

Journal Article↗
PubMed2000

Breakdown of stabilization of atoms interacting with intense, high-frequency laser pulses

An analysis of the influence of the magnetic field of an intense, high-frequency laser pulse on the stabilization of an atomic system is presented. We demonstrate that at relatively modest intensities the magnetic field can significantly alter the dynamics of the system. In particular, a breakdown of stabilization occurs, thereby restricting the intensity regime in which the atom is relatively stable against ionization. Counterpropagating pulses do not negate the detrimental effects of the magnetic field. We compare our quantum mechanical results with classical Monte Carlo simulations.

Journal Article↗
PubMed1975

Representation of cochlea within primary auditory cortex in the cat.

The representation of sound frequency (and of the cochlear partition) within primary auditory cortex has been investigated with use of microelectrode-mapping techniques in a series of 25 anesthetized cats. Among the results were the following: 1) Within vertical penetrations into AI, best frequency and remarkably constant for successively studied neurons across the active middle and deep cortical layers. 2) There is an orderly representation of frequency (and of represented cochlear place) within AI. Frequency is rerepresented across the mediolateral dimension of the field. On an axis perpendicular to this plane of rerepresentation, best-frequency (represented cochlear place) changes as a simple function of cortical location. 3) Any given frequency band (or sector of the cochlear partition) is represented across a belt of cortex of nearly constant width that runs on a nearly straight axis across AI. 4) There is a disproportionately large cortical surface representation of the highest-frequency octaves (basal cochlea) within AI. 5) The primary and secondary field locations were somewhat variable, when referenced to cortical surface landmarks. 6) Data from long penetrations passing down the rostral bank of the posterior ectosylvian sulcus were consistent with the existence of a vertical unit of organization in AI, akin to cortical columns described in primary visual and somatosensory cortex. 7) Responses to tonal stimuli were encountered in fields dorsocaudal, caudal, ventral, and rostral to AI. There is an orderly representation of the cochlea within the field rostal to AI, with a reversal in best frequencies across its border with AI. 8) Physiological definitions of AI boundaries are consistent with their cytoarchitectonic definition. Some of the implications of these findings are discussed.

Acoustic Stimulation↗
PubMed1973

Sirenomelia.

Explore the source record for details and available documents.

Adult↗
PubMed1970

Effect of bile acid deconjugation on the fecal excretion of steroids.

The effect of microbiological deconjugation of bile acids on total bile acid and neutral sterol fecal excretion by adult male rats has been studied. A screening method utilizing mice allowed selection of a Clostridium perfringens type A strain, which accelerated cholesterol catabolism in mice. When this species of bacteria was associated with germfree rats, the fecal bile acids were excreted as free bile acids (deconjugated), however the quantities of bile acids excreted were not increased compared with those of germfree rats. Conventional rats excrete twice as much bile acids (all deconjugated) as do the germfree and C. perfringens-associated rats. It is, therefore, unlikely that the microbiological deconjugation of bile acids is responsible for the increased fecal excretion of bile acids seen in conventional rats. The C. perfringens-associated rats excreted identical kinds and quantities of fecal neutral sterols as did the germfree rats.

Animals↗