Generalized limits for single-parameter quantum estimation

We develop generalized bounds for quantum single-parameter estimation problems for which the coupling to the parameter is described by intrinsic multisystem interactions. For a Hamiltonian with k-system parameter-sensitive terms, the quantum limit scales as 1/Nk, where N is the number of systems. These quantum limits remain valid when the Hamiltonian is augmented by any parameter-independent interaction among the systems and when adaptive measurements via parameter-independent coupling to ancillas are allowed.     

Self-collimation and beam splitting in low-index photonic crystals

We study self-collimation and beam splitting in low-refractive-index photonic crystals created within chalcogenide glass. We propose a beam splitter structure that allows direct experimental verification of photonic-crystal effects at optical wavelengths in a straightforward and definitive manner. The beam splitter provides angular separation of 90° using a highly compact spatial footprint, thus delivering direct application in highly integrated photonic devices.     

Joint seismic-infrasonic processing of recordings from a repeating source of atmospheric explosions

A database has been established of seismic and infrasonic recordings from more than 100 well-constrained surface explosions, conducted by the Finnish military to destroy old ammunition. The recorded seismic signals are essentially identical and indicate that the variation in source location and magnitude is negligible. In contrast, the infrasonic arrivals on both seismic and infrasound sensors exhibit significant variation both with regard to the number of detected phases, phase travel times, and phase amplitudes, which would be attributable to atmospheric factors. This data set provides an excellent database for studies in sound propagation, infrasound array detection, and direction estimation.     

The millimeter wave rotational spectrum of pyruvic acid

The rotational spectrum of pyruvic acid has been investigated for the first time in the millimeter-wave region, at 160-314 GHz, and also in supersonic expansion, at 10-17.4 GHz. The analysis of the broadband spectra recorded in this work was carried out with the newly developed AABS software package for Assignment and Analysis of Broadband Spectra, and precise spectroscopic constants are reported for the ground state, the first excited state of the low-frequency skeletal torsional mode ν₂₄, and the first excited state of the methyl torsional mode ν₂₃. Limited results have also been obtained for several higher excited states. The dataset for the ground state currently exceeds 1500 lines and for both the A and E internal rotor sublevels spans the complete range of values of K_a at the mid values of J for the measured transitions. The results were analysed with three freely available computer programs employing different strategies for dealing with internal rotation and a comparative discussion of their merits is made.     

Variations in recorded acoustic gunshot waveforms generated by small firearms

Analysis of recorded acoustic gunshot signals to determine firearm waveform characteristics requires an understanding of the impulsive signal events, how the waveforms vary among different sources, and how the waveforms are affected by the environment and the recording system. This paper presents empirical results from waveforms produced by different small firearms and an analysis of their variations under different and controlled conditions. Acoustic signals were generated using multiple firearm makes and models firing different ammunition types. Simultaneous recordings from the microphones located at different distances from the source and at different azimuth angles (from the line-of-fire) were used to study source characteristics and sound propagation effects. The results indicate that recorded gunshot waveforms generally consist of multiple acoustic events, and these are observable depending on the received distance and azimuth angle. The source blast size, microphone distance, and microphone azimuth angle are the primary factors affecting the recorded muzzle blast characteristics. Ground or object reflections and ballistic shockwaves and their reflections can interfere with the muzzle blast waveform and its measurements. This experiment confirmed and quantified the wide range of correlation results between waveforms recorded from different source, microphone distance, and microphone angle configurations.     

n-Type GaAs/AlGaAs heterostructure detector with a 3.2 THz threshold frequency

Terahertz detection using the free-carrier absorption requires a small internal work function of the order of a few millielectron volts. A threshold frequency of 3.2 THz (93 microm or approximately 13 meV work function) is demonstrated by using a 1 x 10(18) cm(-3) Si-doped GaAs emitter and an undoped Al(0.04)Ga(0.96)As barrier structure. The peak responsivity of 6.5 A/W, detectivity of 5.5 x 10(8) Jones, and quantum efficiency of 19% were obtained at 7.1 THz under a bias field of 0.7 kV/cm at 6 K, while the detector spectral response range spans from 3.2 to 30 THz.     

Ultra-Precise Mass Measurements Using the UW-PTMS

Based on the use of a single ion, isolated at the center of a cryogenically cooled Penning trap, an environment is produced which makes this mass spectrometer remarkably free of systematic errors. The most notable developments in our quest for an ultra-high accuracy instrument were (a) the compensation of the trapping potential, (b) the discovery that motional sidebands could manipulate radial energies, (c) the use of multiply-charged ions that could improve signal-to-noise, and (d) the use of an ultra-stable superconducting magnet/cryostat system with drift <0.010 ppb/h. The dominant systematic errors are associated with radial electric fields caused by image charges in the trap electrodes and with the rf-electrical drive field used to determine the harmonic axial resonance. To illustrate the potential of this improved spectrometer, the four-fold improved measurement of the proton's mass and the eight-fold improved measurement of oxygen's atomic mass will be described. This revised version was published online in July 2006 with corrections to the Cover Date.     

Representation of Isotropic Turbulence by Scalar Functions

The maximum number N(n) of scalar functions of wavevector needed to represent the general cumulant of order n of isotropic turbulence is determined. In addition to reproducing the known results that N(2) = 1, N(3) = 2, it is shown that N(4) = 4, N(5) = 4, N(6) = 9, etc.     

Statistical analyses of electromyographic activity in spasmodic dysphonic and normal control subjects

Heterogeneity in the quality and task sensitivity of vocal symptoms in the spasmodic dysphonia (SD) population contributes to controversy as to whether this is a single disorder or two disorders with different etiologies (neurogenic versus psychogenic). Perceptual and acoustic assessments of vocal symptoms are inadequate to resolve this controversy. However, myoelectric events are intimately proximal to the source of vocal disruption and may be informative. The present report employs statistical modeling of quantitative amplitude measures of electromyographic activity recorded from thyroarytenoid to examine neuromotor bases of vocal symptoms in SD. Consideration of perceptual ratings of the quality and task sensitivity of vocal symptoms in the context of statistical models provides support for the conclusion that the range of vocal symptoms identified as SD represents a single, neurogenic disorder.