A characterization of the scattered acoustic intensity field in the resonance region for simple spheres

The properties of the scattered acoustic vector fields generated by simple spheres illuminated by monotonic continuous wave (CW) plane waves are investigated. Analytical solutions are derived from general acoustic pressure scattering models and analyzed for wave numbers in the resonance region. Of particular interest is the understanding of the characteristics of the scattered acoustic vector field in the near-to-far-field transition region. The separable active and reactive components of the acoustic intensity are used to investigate the structural features of the scattered field components. Numerical results are presented for the near and transition regions for a rigid sphere. A method of mapping nulls in the scattered intensity field components is described. The analysis is then extended to include a simple fluid-filled boundary and finally the evacuated thin-walled shell. Near field acoustic intensity field structures are compared against mechanical material properties of vacuous shells. The ability to extract scattered field features is illustrated with measurements obtained from a recent in-air experiment using an anechoic chamber and acoustic vector sensor probes to measure the scattered acoustic vector field from rigid spheres.     

Probing the independence of formant control using altered auditory feedback

Two auditory feedback perturbation experiments were conducted to examine the nature of control of the first two formants in vowels. In the first experiment, talkers heard their auditory feedback with either F1 or F2 shifted in frequency. Talkers altered production of the perturbed formant by changing its frequency in the opposite direction to the perturbation but did not produce a correlated alteration of the unperturbed formant. Thus, the motor control system is capable of fine-grained independent control of F1 and F2. In the second experiment, a large meta-analysis was conducted on data from talkers who received feedback where both F1 and F2 had been perturbed. A moderate correlation was found between individual compensations in F1 and F2 suggesting that the control of F1 and F2 is processed in a common manner at some level. While a wide range of individual compensation magnitudes were observed, no significant correlations were found between individuals' compensations and vowel space differences. Similarly, no significant correlations were found between individuals' compensations and variability in normal vowel production. Further, when receiving normal auditory feedback, most of the population exhibited no significant correlation between the natural variation in production of F1 and F2.     

Bending insensitivity of fiber Bragg gratings in suspended-core optical fibers

This Letter presents simulation and experimental results that explore bending insensitivity of fiber Bragg gratings in suspended-core optical fibers. The implementation of thin silica bridge in the fibers enhances index contrast of the fiber core and reduces bending-induced strain transfer to the fiber core. This fiber design lead to a reduction of over 7 times in strain-induced fiber Bragg grating resonant peak shifts in the suspended-core fiber compared with that in standard telecommunication fiber, and an 0.14 dB bending loss at a bending radius of 6.35 mm.     

Feedback localization of freely diffusing fluorescent particles near the optical shot-noise limit

We report near-optimal tracking of freely diffusing fluorescent particles in a quasi-two-dimensional geometry via photon counting and real-time feedback. We present a quantitative statistical model of our feedback network and find excellent agreement with the experiment. We monitor the motion of a single fluorescent particle with a sensitivity of 15 nm/sqrt Hz while collecting fewer than 5000 fluorescence photons/s. Fluorescent microspheres (diffusion coefficient 1.3 microm2/s) are tracked with a root-mean-square tracking error of 170 nm, within a factor of 2 of the theoretical limit set by photon counting shot noise.     

Two-dimensional infrared spectroscopy detected by chirped pulse upconversion

A two-dimensional (2D) infrared spectrum of Mn2(CO)10 is measured by using chirped-pulse upconversion (CPU) of the nonlinear signal field plus a reference local oscillator. By converting the spectrum to the visible, a silicon CCD camera can be used. The method offers an attractive alternative to direct IR detection due to the technological maturity of silicon and its greater intrinsic detectivity over HgCdTe. Using CPU, we acquired a rephasing 2D IR spectrum in a few seconds.     

Application of Mie theory to determine the structure of spheroidal scatterers in biological materials

We present here the results of a numerical study on light scattering from nonspherical particles with relevance to detecting precancerous states in epithelial tissues. In previous studies of epithelial cell nuclei, the experimental light scattering data have been analyzed by comparison with Mie theory. However, given the spheroidal shape of many cell nuclei, the validity of this assumption demands a thorough investigation. We investigate this assumption by using the T-matrix method to model light scattered from spheroids with parameters relevant to epithelial cell nuclei. In our previous studies, we have developed a data analysis procedure that extracts the oscillatory component of the angular-scattering distribution for an ensemble of epithelial cell nuclei for comparison with Mie theory. We demonstrate that application of our analysis procedure to the predictions of the T-matrix method for spheroids, oriented such that their axis of symmetry is aligned with the incident light propagation direction, generally yields the spheroid dimension that is transverse to the incident light propagation direction with subwavelength accuracy.     

3D MRI of non-Gaussian (3)He gas diffusion in the rat lung

In (3)He magnetic resonance images of pulmonary air spaces, the confining architecture of the parenchymal tissue results in a non-Gaussian distribution of signal phase that non-exponentially attenuates image intensity as diffusion weighting is increased. Here, two approaches previously used for the analysis of non-Gaussian effects in the lung are compared and related using diffusion-weighted (3)He MR images of mechanically ventilated rats. One approach is model-based and was presented by Yablonskiy et al., while the other approach utilizes the second order decay contribution that is predicted from the cumulant expansion theorem. Total lung coverage is achieved using a hybrid 3D pulse sequence that combines conventional phase encoding with sparse radial sampling for efficient gas usage. This enables the acquisition of nine 3D images using a total of only approximately 1 L of hyperpolarized (3)He gas. Diffusion weighting ranges from 0 s/cm(2) to 40 s/cm(2). Results show that the non-Gaussian effects of (3)He gas diffusion in healthy rat lungs are directly attributed to the anisotropic geometry of lung microstructure as predicted by the Yablonskiy model, and that quantitative analysis over the entire lung can be reliably repeated in time-course studies of the same animal.     

An improved algorithm for computing topological entropy

A new algorithm is presented for computing the topological entropy of a unimodal map of the interval. The accuracy of the algorithm is discussed and some graphs of the topological entropy which are obtained using the algorithm are displayed.     

Observation of eta'c production in gammagamma fusion at CLEO

We report on the observation of the eta(')(c)(2(1)S0), the radial excitation of the eta(c)(1(1)S0) ground state of charmonium, in the two-photon fusion reaction gammagamma-->eta(')(c)-->K(0)(S)K+/-pi(-/+) in 13.6 fb(-1) of CLEO II/II.V data and 13.1 fb(-1) of CLEO III data. We obtain M(eta(')(c))=3642.9+/-3.1(stat)+/-1.5(syst) MeV and M(eta(c))=2981.8+/-1.3(stat)+/-1.5(syst) MeV. The corresponding values of hyperfine splittings between 1S0 and 3S1 states are DeltaM(hf)(1S)=115.1+/-2.0 MeV and DeltaM(hf)(2S)=43.1+/-3.4 MeV. Assuming that the eta(c) and eta(')(c) have equal branching fractions to K(S)Kpi, we obtain Gamma(gammagamma)(eta(')(c))=1.3+/-0.6 keV.