The onset of coulomb explosions in polyatomic molecules

With the development of high intensity femtosecond lasers, the ionisation and dissociation dynamics of molecules has become an area of considerable interest. Using the technique of femtosecond laser mass spectrometry (FLMS), the molecules carbon disulphide, pyrimidine, toluene, cyclohexanone and benzaldehyde are studied with pulse widths of 50 fs in the near infrared (IR) wavelength region (790 nm). Results are presented and contrasted for laser beam intensities around 10(15) and 10(16) W cm(-2). For the lower intensities, the mass spectra yield dominant singly charged parent ions. Additionally, the appearance of doubly charged parent ions is evident for carbon disulphide, toluene and benzaldehyde with envelopes of doubly charged satellite species existing in these local regions. Carbon disulphide also reveals a small triply charged component. Such atomic-like features are thought to be a strong fingerprint of FLMS at these intensities. However, upon increasing the laser intensity to approximately 10(16) W cm(-2), parent ion dominance decreases and the appearance of multiply charged atomic species occurs, particularly carbon. This phenomenon has been attributed to Coulomb explosions in which the fast absorption of many photons may produce transient highly ionised parent species which can subsequently blow apart. Copyright 1999 John Wiley & Sons, Ltd.     

Three-dimensional annihilation imaging of trapped antiprotons

We demonstrate three-dimensional imaging of antiprotons in a Penning trap, by reconstructing annihilation vertices from the trajectories of the charged annihilation products. The unique capability of antiparticle imaging has allowed, for the first time, the observation of the spatial distribution of the particle loss in a Penning trap. The radial loss of antiprotons on the trap wall is localized to small spots, strongly breaking the azimuthal symmetry expected for an ideal trap. Our observations have important implications for detection of antihydrogen annihilations.     

Determination of loads applied perpendicularly to the outer boundary of a ring using coefficients of influence

A procedure is explained to determined the amount of several pairs of diametrical loads applied to the outside boundary of a ring when stresses at selected points of the inside or outside boundaries are known. Coefficients of influence are used, following an approach similar to the one presented in a previous paper. Examples of application are given and the possible increase in precision is shown when the number of points of measurements is larger than the number of loads to be determined.     

Observation of the developing optical continuum along a nonlinear waveguide

We describe what is to our knowledge the first nondestructive measurement of the evolution of an optical continuum as a function of distance along a nonlinear waveguide. Spectral mapping is achieved on a subwavelength scale by utilizing near-field microscopy to probe the waveguide's evanescent field. The measured continuum broadening along the waveguide agrees in general form with predictions of broadening from theoretical calculations, but differs in some important details. Subwavelength resolution measurements are made both along and across the waveguide to reveal spectral variations not seen before by other techniques.     

CIDNP study of the photocleavage of benzyl derivatives

Evidence of the mechanistic pathways involved in the acetone sensitized homolytic photocleavage of benzyltrialkylammonium salts and other benzyl derivatives is obtained by CIDNP.     

Evidence for Ps formation in spurs in high-density gaseous CO2

Measurements of Ps yields in mixtures of CO₂ and Ar with the electron scavengers CCl₄ and CCl₂F₂ are reported. It is shown that the CO₂ mixtures provide direct evidence for Ps formation in spurs in this gas. Further, some support is also given to recent models which consider Ps formation in gases by both Ore and spur processes. The results obtained for the Ar mixtures are consistent with the Ore model of Ps formation.     

Determination of natural responses of mechanical systems using correlation techniques

The natural responses of linear systems may be found by observation of the system's response to a known stimulus. In such tests, the observations required ore the response as a function of time when the stimulus is deterministic in form. In practical situations, the application of this method is often hampered by the presence in the response of extraneous noise and the necessity of using large-amplitude excitations. The difficulties of the method outlined may be avoided by using random stimuli and cross correlations to obtain a statistical estimate of the natural modes. This paper describes one application in which the critical speeds and relative deflection amplitudes of a machine shaft-rotor system were found with the system either stationary or running at some arbitrary speed.     

A vibrational spectroscopic study of TiCl3

The α-, β- and γ-isomorphs of TiCl₃ have been investigated using Raman spectroscopy. For this purpose a cell was designed specially for air sensitive compounds. The possibility of resonance effects in the Raman spectrum is discussed and some evidence is found for a pre-resonance Raman spectrum for the β-isomorph. Infra-red spectra are discussed in terms of the different types of lattice found in TiCl₃.     

Measurements of nuclear data of minor actinides for transmutation of high-level waste

For nuclear transmutation of minor actinides, delayed neutron emission measurement for²⁴¹Am was carried out in thermal neutron irradiation location. The neutron capture cross sections of²⁴¹Am were also measured radiochemically. The transmutation process of²⁴¹Am in reactor is discussed by calculating the yields of minor actinides with the nuclear data measured in this study and the evaluated values. The accelerator driven transmutation of minor actinides by high-flux neutrons from spallation reactions is also presented.     

Vocal cues indicate level of arousal in infant African elephant roars

Arousal-based physiological changes influence acoustic features of vocalizations in mammals. In particular, nonlinear phenomena are thought to convey information about the caller's arousal state. This hypothesis was tested in the infant African elephant (Loxodonta africana) roar, a call type produced in situations of arousal and distress. Ninety-two percent of roars exhibited nonlinear phenomena, with chaos being the most common type. Acoustic irregularities were strongly associated with elevated fundamental frequency values. Roars produced in situations of highest urgency, based on the occurrence of behavioral indicators of arousal, were characterized by the lowest harmonics-to-noise ratio; this indicates low tonality. In addition, roars produced in these situations lasted longer than those produced in contexts of lower presumed urgency. Testing the infant roars for individual distinctiveness revealed only a moderate classification result. Combined, these findings indicate that infant African elephant roars primarily function to signal the caller's arousal state. The effective communication of this type of information may allow mothers to respond differentially based on their infant's degree of need and may be crucial for the survival of infant African elephants in their natural environment.