Frequency glides in the impulse responses of auditory-nerve fibers

Previous reports of frequency modulations, or glides, in the impulse responses of the auditory periphery have been limited to analyses of basilar-membrane measurements and responses of auditory-nerve (AN) fibers with best frequencies (BFs) greater than 1.7 kHz. These glides increased in frequency as a function of time. In this study, the instantaneous frequency as a function of time was measured for impulse responses of AN fibers in the cat with a range of BFs (250-4500 Hz). Impulse responses were estimated from responses to wideband noise using the reverse-correlation technique. The impulse responses had increasing frequency glides for fibers with BFs greater than 1500 Hz, nearly constant frequency as a function of time of BFs between 750 and 1500 Hz, and decreasing frequency glides for BFs below 750 Hz. Over the levels tested, the glides for fibers at all BFs were nearly independent of stimulus level, consistent with previous reports of impulse responses of the basilar membrane and AN fibers. Implications of the different glide directions observed for different BFs are discussed, specifically in relation to models for the auditory periphery as well as for the derivation of impulse responses for the human auditory periphery based on psychophysical measurements.     

“Age” determination of irradiated materials utilizing inductively coupled plasma mass spectrometric (ICP-MS) detection

A gas pressurized extraction chromatography (GPEC) system has been developed to perform elemental separations on radioactive samples to determine total and isotopic compositions of Cs and Ba from an irradiated salt sample, fuel sample and two sealed radiation sources. The GPEC system employs compressed nitrogen to move liquid through the system, compared to gravity or pumped liquids that are typically used for separations. A commercially available Sr-Resin™ was used to perform the separation for the above mentioned analytes. A 1% acetic acid solution was determined to be the best extractant for Ba. A flow rate of 0.1 mL/min was determined to be optimal for the separation of Ba. Complete recovery of the Cs and Ba was achieved, within the systematic uncertainties of the experiments.     

Compound Poisson Law for Hitting Times to Periodic Orbits in Two-Dimensional Hyperbolic Systems

We show that a compound Poisson distribution holds for scaled exceedances of observables \(\phi \) uniquely maximized at a periodic point \(\zeta \) in a variety of two-dimensional hyperbolic dynamical systems with singularities \((M,T,\mu )\), including the billiard maps of Sinai dispersing billiards in both the finite and infinite horizon case. The observable we consider is of form \(\phi (z)=-\ln d(z,\zeta )\) where d is a metric defined in terms of the stable and unstable foliation. The compound Poisson process we obtain is a Pólya-Aeppli distibution of index \(\theta \). We calculate \(\theta \) in terms of the derivative of the map T. Furthermore if we define \(M_n=\max \{\phi ,\ldots ,\phi \circ T^n\}\) and \(u_n (\tau )\) by \(\lim _{n\rightarrow \infty } n\mu (\phi >u_n (\tau ) )=\tau \) the maximal process satisfies an extreme value law of form \(\mu (M_n \le u_n)=e^{-\theta \tau }\). These results generalize to a broader class of functions maximized at \(\zeta \), though the formulas regarding the parameters in the distribution need to be modified.     

beta-Hematin (hemozoin) mediated decompostion of polyunsaturated fatty acids to 4-hydroxy-2-nonenal

beta-Hematin is an important heme metabolite of malarial infection. Its role as an agent mediating the formation of the reactive electrophile 4-hydroxynonenal (HNE) from polyunsaturated fatty acids was investigated. In vitro formation of HNE was found to be facilitated by the presence of hemozoin in a concentration-dependent fashion. The reactivity of HNE derived from reaction with beta-hematin was confirmed through its ability to form protein adducts on myoglobin.     

Computational lens for the near field

A method is presented to reconstruct the structure of a scattering object from data acquired with a photon scanning tunneling microscope. The data may be understood to form a Gabor type near-field hologram and are obtained at a distance from the sample where the field is defocused and normally uninterpretable. Object structure is obtained by the solution of the inverse scattering problem within the accuracy of a perturbative, two-dimensional model of the object.     

Isolation and synthesis of 2-chloro-10-α-hydroxynaltrexone, a new naltrexone degradant

The putative structure of a new degradant from REVIA® tablets was assigned 2-chloro-10-α-hydroxynaltrexone 2. A route for the independent synthesis was developed wherein a N,N-diethylcarbamate derivative directed an ortho-metallation of the naltrexone nucleus, leading to the desired 2-chloro functionality. Oxidation of the 10-position, followed by deprotection provided 2, which was identical in all respects to the original isolate.     

Search for non-strange baryonium states in the baryon exchange reaction K−p → Y0pp at 18.5 GeV/c

Narrow baryonium production in the baryon exchange reactions $\text{K}{}^{\mathrm{?}}\text{p}\text{→ Λ}\text{p}\text{p}$ and $\text{K}{}^{\mathrm{?}}\text{p}\text{→}\text{pK}{}^{\mathrm{?}}\text{p}\text{p}$ at 18.5 GeV/c is investigated in a 12 events/nb experiment performed at the CERN Ω′ spectrometer. No narrow structure is observed in the $\text{p}\text{p}$ mass spectra. Upper limits for production of baryonium states are given as a function of $\text{p}\text{p}$ mass.