Ab initio study of the interaction of CHX3 (X = H, F, Cl, or Br) with benzene and hexafluorobenzene

In this paper, the results of a study of the interaction of methane, fluoroform, chloroform, and bromoform with benzene and hexafluorobenzene are presented. The benzene complexes were studied at the MP2/6-31G(d) and MP2/6-311++G(2d,p) levels, and the hexafluorobenzene complexes were only studied at the MP2/6-31G(d) level. The optimized geometries, stabilization energies, potential energy surfaces, harmonic frequencies, and vibrational intensities are reported. A net attraction is predicted for all four benzene complexes, whereas for the CHX3.C6F6 complexes, it was found that MP2/6-31G(d) predicts a net attraction for the CH4, CHCl3, and CHBr3 complexes and does not predict a stable complex for CHF3.C6F6. The three complexes with net attractions all have blue-shifts of the CHX3 CH stretching wavenumber and a slight contraction (0.001-0.003 A) of the CH bond in CHX3. The MP2/6-31G(d) level predicts that the intensity of the CHX3 CH stretch will vary widely. For CH4.C6H6 and CHF3.C6H6, it is predicted that the intensity will be smaller for the complexes than the free molecules, whereas for the other complexes, anywhere from a 30% increase to an increase of 87 times is predicted. The atoms in molecules analysis showed that only three of the eight criteria for normal hydrogen bonding are satisfied for all eight complexes studied. Criterion 3 (value of the Laplacian at the bond critical point) is not satisfied for any of the eight complexes.     

Temperature dependence of the optical properties of liquid benzene in the infrared between 25 and 50 degrees C

The vibrational properties of benzene have long been a topic of interest. A recent comparison presented in the literature of the liquid and gas intensities at 25 degrees C have revealed some intriguing results regarding how the interaction between the hydrogens and the neighbouring pi-clouds in the liquid affect the vibrational intensities. To gain insight into the effect of temperature on the optical properties of liquid benzene and these interactions, the optical constants of liquid benzene have been determined through transmission measurements between 7,400 and 800 cm(-1). The spectra were measured in cells with KBr windows over a path length range of 15-1,000 microm and were collected over a temperature range of 30-50 degrees C in 5 degrees C increments. Variations in the imaginary molar polarizability spectra are examined and compared to a similar study of liquid toluene completed several years ago.     

Theory of forward and reverse middle-ear transmission applied to otoacoustic emissions in infant and adult ears

The purpose of this study is to understand why otoacoustic emission (OAE) levels are higher in normal-hearing human infants relative to adults. In a previous study, distortion product (DP) OAE input/output (I/O) functions were shown to differ at f2 = 6 kHz in adults compared to infants through 6 months of age. These DPOAE I/0 functions were used to noninvasively assess immaturities in forward/reverse transmission through the ear canal and middle ear [Abdala, C., and Keefe, D. H., (2006). J. Acoust Soc. Am. 120, 3832-3842]. In the present study, ear-canal reflectance and DPOAEs measured in the same ears were analyzed using a scattering-matrix model of forward and reverse transmission in the ear canal, middle ear, and cochlea. Reflectance measurements were sensitive to frequency-dependent effects of ear-canal and middle-ear transmission that differed across OAE type and subject age. Results indicated that DPOAE levels were larger in infants mainly because the reverse middle-ear transmittance level varied with ear-canal area, which differed by more than a factor of 7 between term infants and adults. The forward middle-ear transmittance level was -16 dB less in infants, so that the conductive efficiency was poorer in infants than adults.     

Wideband ipsilateral measurements of middle-ear muscle reflex thresholds in children and adults

The goals of the current study were to: 1) evaluate the feasibility of a new wideband approach to measuring middle-ear muscle reflex (MEMR) status, and 2) to test the hypothesis that ipsilateral thresholds elicited with 1 or 2 kHz tones and broadband noise activators on a wideband acoustic transfer function (WATF) system are lower than thresholds elicited on a clinical system. Clinical MEMR tests have limitations, including the need for high activator levels to elicit a shift in a narrowband probe (e.g., a 0.226 or 1 kHz tone). Wideband MEMR tests using WATFs may elicit the reflex at lower levels because a wideband probe (click) is used and the threshold detection criterion can be wideband. Mean wideband MEMR thresholds across 40 normal-hearing adult ears were 2.2-4.0 dB lower than clinical MEMR thresholds, depending on the activator and specific WATF test used (admittance magnitude or energy reflectance). Wideband MEMR has potential clinical utility beyond the adult population, including use in newborn and preschool hearing screenings. In a newborn hearing screening, for example, wideband MEMR could be completed with the same system as otoacoustic emissions. However, further investigations in infants and young children are needed.     

Ear asymmetries in middle-ear, cochlear, and brainstem responses in human infants

In 2004, Sininger and Cone-Wesson examined asymmetries in the signal-to-noise ratio (SNR) of otoacoustic emissions (OAE) in infants, reporting that distortion-product (DP)OAE SNR was larger in the left ear, whereas transient-evoked (TE)OAE SNR was larger in the right. They proposed that cochlear and brainstem asymmetries facilitate development of brain-hemispheric specialization for sound processing. Similarly, in 2006 Sininger and Cone-Wesson described ear asymmetries mainly favoring the right ear in infant auditory brainstem responses (ABRs). The present study analyzed 2640 infant responses to further explore these effects. Ear differences in OAE SNR, signal, and noise were evaluated separately and across frequencies (1.5, 2, 3, and 4 kHz), and ABR asymmetries were compared with cochlear asymmetries. Analyses of ear-canal reflectance and admittance showed that asymmetries in middle-ear functioning did not explain cochlear and brainstem asymmetries. Current results are consistent with earlier studies showing right-ear dominance for TEOAE and ABR. Noise levels were higher in the right ear for OAEs and ABRs, causing ear asymmetries in SNR to differ from those in signal level. No left-ear dominance for DPOAE signal was observed. These results do not support a theory that ear asymmetries in cochlear processing mimic hemispheric brain specialization for auditory processing.     

Simple and robust approach for passivating and functionalizing surfaces for use in complex media

Pluronic is a popular triblock copolymer used as a surfactant to introduce hydrophilic coatings onto many different types of material surfaces, from engineering to biomedical applications. Unfortunately, this is limited in its ability to resist fouling from complex media (i.e., blood) and leaves the surface hard for further modification. Herein, we report a simple, yet robust approach for passivating and functionalizing surfaces based on zwitterionic poly(carboxybetaine) (PCB) based triblock copolymer, which can be directly applied to surfaces to prevent nonspecific protein adsorption from undiluted blood plasma, and to provide additional functionalities needed for the attachment of biomolecules. Several hydrophobic surfaces including polydimethylsiloxane, silanized silica, and self-assembled monolayers are tested to demonstrate its applicability to a wide range of systems. This approach provides a robust, convenient, and effective surface modification method for real-world applications from simple surface passivation to specific targeting in complex media.     

3-d chemical imaging using angle-scan nanotomography in a soft X-ray scanning transmission X-ray microscope

Three-dimensional chemical mapping using angle scan nanotomography in a soft X-ray scanning transmission X-ray microscope (STXM) has been used to investigate the spatial distributions of a low density polyacrylate polyelectrolyte ionomer inside submicron sized polystyrene microspheres. Acquisition of tomograms at multiple photon energies provides true, quantifiable 3-d chemical sensitivity. Both pre-O 1s and C 1s results are shown. The study reveals aspects of the 3-d distribution of the polyelectrolyte that were inferred indirectly or had not been known prior to this study. The potential and challenges for extension of the technique to studies of other polymeric and to biological systems is discussed.     

CD40mAb adjuvant induces a rapid antibody response that may be beneficial in post-exposure prophylaxis

Active vaccination can be effective as a post-exposure prophylaxis, but the rapidity of the immune response induced, relative to the incubation time of the pathogen, is critical. We show here that CD40mAb conjugated to antigen induces a more rapid specific antibody response than currently used immunological adjuvants, alum and monophosphoryl lipid A™.     

Dynamical eigenfunction decomposition of turbulent channel flow

The results of an analysis of low-Reynolds-number turbulent channel flow based on the Karhunen-Loéve(K-L) expansion are presented. The turbulent flow field is generated by a direct numerical simulation of the Navier-Stokes equations at a Reynolds number Re,= 80 (based on the wall shear velocity and channel half-width). The K-L procedure is then applied to determine the eigenvalues and eigenfunctions for this flow. The random coefficients of the K-L expansion are subsequently found by projecting the numerical flow field onto these eigenfunctions. The resulting expansion captures 90% of the turbulent energy with significantly fewer modes than the original trigonometric expansion. The eigenfunctions, which appear either as rolls or shearing motions, posses viscous boundary layers at the walls and are much richer in harmonics than the original basis functions. Chaotic temporal behaviour is observed in all modes and increases for higher-order eigenfunctions. The structure and dynamical behaviour of the eigenmodes are discussed as well as their use in the representation of the turbulent flow.