On a zero equation model of turbulence

In this paper we study a widely used zero equation model of turbulence. The governing equations are derived by applying to the incompressible Navier-Stokes equations the Reynolds time averaging procedure. We achieve closure by employing the eddy viscosity concept. Using the Implicit Function Theorem we obtain an existence and uniquencess result. We also discuss the existence of nonsingular solutions. Finally, we present an algorithm for solving the modeled equations.     

Radiative lifetimes of ions measured with the photoelectron spectrometer

Using a modified photoelectron spectrometer the radiative lifetimes of some electronically excited diatomic and triatomic molecular ions have been determined. The method is based on measuring the time delay between the ejection of a photoelectron from a molecule and the emission of a photon from the resulting ion.     

Spectra and structure of organogermanes: Part XX. Infrared and Raman spectra of (CH3)3GeNCO and (CH3)3GeNCS

The infrared and Raman spectra of gaseous and solid (CH₃)₃ GeNCO and solid (CH₃)₃GeNCS have been recorded over the frequency range 20–4000 cm^?1 . The Raman spectra of the liquids have also been recorded. Assignments of the normal modes have been made on the bases of band types, Raman depolarization values, and characteristic frequencies. Spectral data indicate that (CH₃)₃ GeNCO is non-linear in all phases and that (CH₃)₃GeNCS has a linear or quasi-linear heavy atom skeleton in the fluid phases.     

Fission track mapping of uranium in black spruce (Picea Mariana) twigs

Fission track analysis (FTA) has been used to investigate the biological uptake of uranium. Examination of fission track maps of black spruce twigs (from areas of uranium mineralization and mill tailings) shows uranium to be concentrated in the inner bark while decreasing in the outer bark of the twigs. Track clusters in the bark, too large to be uraniferous airborne particulate matter, are identified as being associated with resin canals in the twigs. The results of this work help clarify the mechanisms by which uranium is incorporated in black spruce twigs. The observation of decreasing uranium content with the increasing age of black spruce twigs by an earlier worker, can now be explained by the relative reduction in volume of the uranium enriched inner bark with age.     

Radiation-driven hydrodynamics of high- hohlraums on the national ignition facility

The first hohlraum experiments on the National Ignition Facility (NIF) using the initial four laser beams tested radiation temperature limits imposed by plasma filling. For a variety of hohlraum sizes and pulse lengths, the measured x-ray flux shows signatures of filling that coincide with hard x-ray emission from plasma streaming out of the hohlraum. These observations agree with hydrodynamic simulations and with an analytical model that includes hydrodynamic and coronal radiative losses. The modeling predicts radiation temperature limits with full NIF (1.8 MJ), greater, and of longer duration than required for ignition hohlraums.     

Nonequilibrium raftlike membrane domains under continuous recycling

We present a model for the kinetics of spontaneous membrane domain (raft) assembly that includes the effect of membrane recycling ubiquitous in living cells. We show that domains can have a broad power-law distribution with an average radius that scales with the 1/4 power of the domain lifetime when the line tension at the domain edges is large. For biologically reasonable recycling and diffusion rates, the average domain radius is in the tens of nm range, consistent with observations. This represents one possible link between signaling (involving rafts) and traffic (recycling) in cells. Finally, we present evidence that suggests that the average raft size may be the same for all scale-free recycling schemes.     

Detecting cortical lesions in multiple sclerosis at 7 T using white matter signal attenuation

Cortical lesions have recently been a focus of multiple sclerosis (MS) MR research. In this study, we present a white matter signal attenuating sequence optimized for cortical lesion detection at 7 T. The feasibility of white matter attenuation (WHAT) for cortical lesion detection was determined by scanning eight patients (four relapsing/remitting MS, four secondary progressive MS) at 7 T. WHAT showed excellent gray matter-white matter contrast, and cortical lesions were hyperintense to the surrounding cortical gray matter, The sequence was then optimized for cortical lesion detection by determining the set of sequence parameters that produced the best gray matter-cortical lesion contrast in a 10-min scan. Despite the B1 inhomogeneities common at ultra-high field strengths, WHAT with an adiabatic inversion pulse showed good cortical lesion detection and would be a valuable component of clinical MS imaging protocols.     

Audibility and recognition of stop consonants in normal and hearing-impaired subjects

The purpose of this study was to examine the effect of spectral-cue audibility on the recognition of stop consonants in normal-hearing and hearing-impaired adults. Subjects identified six synthetic CV speech tokens in a closed-set response task. Each syllable differed only in the initial 40-ms consonant portion of the stimulus. In order to relate performance to spectral-cue audibility, the initial 40 ms of each CV were analyzed via FFT and the resulting spectral array was passed through a sliding-filter model of the human auditory system to account for logarithmic representation of frequency and the summation of stimulus energy within critical bands. This allowed the spectral data to be displayed in comparison to a subject's sensitivity thresholds. For normal-hearing subjects, an orderly function relating the percentage of audible stimulus to recognition performance was found, with perfect discrimination performance occurring when the bulk of the stimulus spectrum was presented at suprathreshold levels. For the hearing-impaired subjects, however, it was found in many instances that suprathreshold presentation of stop-consonant spectral cues did not yield recognition equivalent to that found for the normal-hearing subjects. These results demonstrate that while the audibility of individual stop consonants is an important factor influencing recognition performance in hearing-impaired subjects, it is not always sufficient to explain the effects of sensorineural hearing loss.