There have been many studies examining the differences between infant-directed speech (IDS) and adult-directed speech (ADS). However, investigations asking whether mothers clarify vowel articulation in IDS have reached equivocal findings. Moreover, it is unclear whether maternal speech clarification has any effect on a child's developing language skills. This study examined vowel clarification in mothers’ IDS at 0;10–11, 1;6, and 2;0, as compared to their vowel production in ADS. Relationships between vowel space, vowel duration, and vowel variability and child language outcomes at two years were also explored. Results show that vowel space and vowel duration tended to be greater in IDS than in ADS, and that one measure of vowel clarity, a mother's vowel space at 1;6, was significantly related to receptive as well as expressive child language outcomes at two years of age.

Since the discovery of a significant depletion of acetylcholine in discrete areas of the brain of patients affected by Alzheimer's disease, attempts at symptomatic therapy have concentrated on acetylcholine supplementation, an approach that is based upon the efficacy of dopaminergic supplementation therapy for Parkinson's disease. Choline, then lecithin, used orally, failed to improve symptoms but the hypothesis that long-term choline supplementation might stabilize the course of Alzheimer's disease remains to be tested. Nerve growth factor may also offer that possibility. Bethanechol administered intracerebroventricularly did not help when a fixed dose was used but individual titration of more selective muscarinic agonists may prove more effective. In this article we report that tetrahydroaminoacridine (THA), given together with highly concentrated lecithin, appears to bring improvement in cognition and in functional autonomy using the Mini Mental State and the Rapid Disability Rating Scale-2 respectively, without change in behavior as reflected by the Behave-AD. Double-blind cross-over studies are in progress to establish its efficacy. Improvement in study design and means of assessment of cognition, functional autonomy and behavior have been made possible by these drug trials.

This cross-sectional study at a tertiary-care hospital in Botswana from 2000 to 2007 was performed to determine the epidemiologic characteristics of Staphylococcus aureus bacteremia. We identified a high prevalence (11.2% of bacteremia cases) of methicillin-resistant S. aureus (MRSA) bacteremia. MRSA isolates had higher proportions of resistance to commonly used antimicrobials than did methicillin-susceptible isolates, emphasizing the need to revise empiric prescribing practices in Botswana.

We used VLBI observations at 8.4 GHz between 1991 and 2005 to determine the motion of the RS CVn binary IM Pegasi (HR 8703), the guide star for the NASA/Stanford gyroscope relativity mission, Gravity Probe B (GP-B). The motion was determined relative to our primary reference, the core of the quasar 3C 454.3. The stability of this core was checked relative to two other extragalactic sources, B2250+194 and B2252+172, the former of which was tied to the ICRF. The core of 3C 454.3 is stationary relative to these two sources to within 30 μas yr−1 in each coordinate. IM Pegasi's radio morphology varies, but appears to be on average centered on the primary. We estimate the proper motion of IM Pegasi with a statistical standard error (sse) of 30 μas yr−1 in each coordinate. We also estimate the parallax with a statistical standard error of 75 μas and parameters of the orbit with sse's corresponding to 110 μas on the sky. Coupled with our upper limit of three times the sse on any systematic errors in each parameter %threefold higher upper limit on the systematic error contributions to each parameter estimate, these results ensure that the uncertainty of IM Pegasi's proper motion makes only a small contribution to the uncertainty of GP-B's tests of general relativity.

The use of the DNA duplex as a molecular wire is discussed with particular attention to recent experimental findings. Experimental studies of photo-excited hole dynamics in DNA can be understood within the phenomenological hopping model. However a microscopic first principles approach requires taking into account the interaction between charge and duplex degrees of freedom. The nature of possible metallic native DNA behavior is discussed.

The NASA/Stanford Relativity Mission (Gravity Probe B) is to test the unverified “frame-dragging” prediction of general relativity through measurements of the precessions of orbiting gyroscopes. For mission accuracy goals to be met, the proper motion of a “guide star,” whose position will be used as an inertial reference, must be determined in an extragalactic reference frame with a standard error less than 0.5 mas/yr. We discuss our VLBI observations of the current guide-star candidates (radio stars HR 1099, HR 5110, and HR 8703) and our techniques for obtaining differential astrometric positions with the needed accuracy.

We determine the relative separations of the sources in the triangle 1803+784/1928+738/2007+777 with submilliarcsecond accuracy from global 8.4 GHz VLBI observations. We remove the ionospheric contribution to the phase-delay observable using ionospheric total electron content estimates obtained from Global Positioning System (GPS) data. The triangular geometry provides a consistency check through sky closure.

An attractive and challenging approach to the construction of robust, thin film materials with large second-order optical nonlinearities is the covalent self-assembly of aligned arrays of high-β molecular chromophores into multilayer superlattices. In this paper, we describe the dispersion of second harmonic generation (SHG) in a self-assembled (SA) monolayer containing a stilbazolium chromophore. The frequency-dependent measurements were performed on 25 Å thick monolayers on glass using a tunable (0.4–2 μm) light source based on optical parametric amplification (OPA). The SHG spectrum contains a clear two-photon resonance at hω = 1.3eV. The maximum in the second-order susceptibility coincides with a low energy chromophore-centered charge-transfer excitation at 480 nm. The experimental SHG dispersion values compare favorably with theoretical results computed using a sum-over-states (SOS) formalism. However, the measured values exhibit a somewhat broader band response than the theoretical curve, and the origin of this behavior is discussed.

Cryptands and crown ethers increase the cation transport in phosphazene and alkoxyaluminate polyelectrolytes. Vibrational spectroscopy indicates that the increased conductivity originates from reduced ion pairing.

Molecular dynamics simulations performed on highly concentrated Coulomb/solvent systems are used to help interpret the transport mechanism in polymer ionics. Using simple Coulomb and Lennard-Jones forces among the ions and a solvent model of a fixed dipole contained in a spherical solvent particle, we investigated the nature of ion pair formation and stability. For a model NaI system, we find that ion pairs decrease with increase in solvent dipole moment or temperature. The latter observation is at variance with experimental results on polymer electrolytes, probably because of entropy terms that do not occur with our simple solvent molecule.

On 1983 May 10–11 we undertook simultaneous λ3.6 and λ13 cm Mark III VLBI observations of the quasars 1038+528 A,B. Our experimental conditions (i.e., synthesized band, uv-coverage, etc.) were almost identical to those we used on 1981 March 17–18. Thus, we could make a direct comparison of the results from both epochs.

Third-order optical susceptibilities (γijkl) can be efficiently analyzed for a variety of molecular structures employing perturbation theory and a PPP-SCF-SECI-DECI π-electron model Hamiltonian. The key, frequency tripling second hyperpolarizability γijkl(−3ω;ω,ω,ω) is calculated with full single and double CI. It is found that double excitations play a major role in third-order processes, and that γijkl, like the polarizability αij, is sensitive largely to the overall size (volume) of the π system, although charge transfer excitations may also contribute. The frequency dependence of v and correlations between γijkl and conjugation length are found for a series of trans polyenes.

Factors contributing to the polarizability (αij) and frequencydoubling hyperpolarizability (βijk) of 2-(p-dimethylaminophenyl)-6-(pnitrophenyl) benzo(l,2-d:4,5-d′ )blsthiazole (DNBT) are analyzed via perturbation theory and the PPP-SCF-MECI π-electron model Hamiltonian. While the observable part of β (βvec) is clearly identifiable with a small number of charge transfer excitations along the molecular dipole direction, a (and by inference, the second-order hyperpolarizability γ) is more closely related to the overall size (volume) of the π-electron cloud. As a consequence, βvec is far more sensitive to molecular distortions which affect donor-acceptor charge transfer interactions than is π. The more sensitive frequency dependence of βvec can be understood in terms of the three-photon character of this nonlinearity.

In studies of extragalactic radio sources with multiple compact components the determination of which components, if any, are stationary and which moving is of importance. In order to learn about the radio properties of the individual components it is also relevant to be able to register maps made at several wavelengths. Both tasks are usually not possible with VLBI because of the irrecoverable corruption of the fringe phase introduced by the propagation medium and the instrumentation. However, when two or more compact radio sources are separated by only a small angle from each other difference techniques can be used to help tackle both questions.

From five sets of VLBI observations spaced between 1972 and 1981, we estimated the positions of components of the superluminal quasar 3C 345 relative to the position of the single component of the quasar NRAO 512. The relative proper motion of the easternmost component of 3C 345, believed to be the “core”, was found to be 0.02±0.02 mas/yr. This result is consistent with the “core” being stationary and the “jet” components moving with respect to NRAO 512.

Mark III VLBI observations of the pulsars PSR 0329+54 and PSR 1133+16 were made at 2.3 GHz using antennas with diameters and locations as follows: 100m, Effelsberg, West Germany (but only for SPR 0329+54); 43m Green Bank, WV, USA; and 40m, Big Pine, CA, USA. The Mark III processor at the Haystack Observatory was “gated” to compute visibility amplitudes and phases as a function of pulsar longitude. This method allowed a) an improvement of the signal to noise ration, by as much as a factor of ten in the case of PSR 1133+16, and b) an interferometric investigation of the pulse structure.