Sounds heard over headphones are typically perceived inside the head (internalized), unlike real sound sources which are perceived outside the head (externalized). If the acoustical waveforms from a real sound source are reproduced precisely using headphones, auditory images are appropriately externalized and localized. The filtering (relative boosting, attenuation and delaying of component frequencies) of a sound by the head and outer ear provides information about the location of a sound source by means of the differences in the frequency spectra between the ears as well as the overall spectral shape. This location-dependent filtering is explicitly described by the head-related transfer function (HRTF) from sound source to ear canal. Here we present sounds to subjects through open-canal tube-phones and investigate how accurately the HRTFs must be reproduced to achieve true three-dimensional perception of auditory signals in anechoic space. Listeners attempted to discriminate between 'real' sounds presented from a loudspeaker and 'virtual' sounds presented over tube-phones. Our results show that the HRTFs can be smoothed significantly in frequency without affecting the perceived location of a sound. Listeners cannot distinguish real from virtual sources until the HRTF has lost most of its detailed variation in frequency, at which time the perceived elevation of the image is the reported cue.

The effect of short-chain branching (SCB) on the persistence length l p of polyethylene (PE) was studied using small-angle neutron scattering (SANS). In thermodynamically good solvents, l p can be measured directly from the scattering vector q tr at the crossover from good solvent mass-fractal scaling to the rodlike persistent scaling, using the unified equation described in the text. The method was used to study l p of both linear and branched PE in deuterated p-xylene, which is a good solvent for PE at 125 °C. The results indicate an increase in l p of the backbone chain with increasing SCB content, independently measured using Fourier transform infrared spectroscopy (FTIR). These results corroborate the behavior previously reported in Monte Carlo simulations of short-chain branched polymers. A functional relationship for l p in terms of the number of SCBs is proposed.

A methodology termed membrane-interaction QSAR (MI-QSAR) analysis has been developed in order to predict the behavior of organic compounds interacting with the phospholipid-rich regions of biological membranes. One important application of MI-QSAR analysis is to estimate ADME properties including the transport of organic solutes through biological membranes as a computational approach to forecasting drug intestinal absorption. A training set of 30 structurally diverse drugs, whose permeability coefficients across the cellular membranes of Caco-2 cells were measured, was used to construct significant MI-QSAR models of Caco-2 cell permeation. Cellular permeation is found to depend primarily upon aqueous solvation free energy (solubility) of the drug, the extent of drug interaction with a model phospholipid (DMPC) monolayer, and the conformational flexibility of the solute within the model membrane. A test set of eight drugs was used to evaluate the predictivity of the MI-QSAR models. The permeation coefficients of the test set compounds were predicted with the same accuracy as the compounds of the training set.

We have studied the thermal behavior of amphiphilic, symmetric triblock copolymers having short, deuterated polystyrene (PS) end blocks and a large poly(N-isopropylacrylamide) (PNIPAM) middle block exhibiting a lower critical solution temperature (LCST) in aqueous solution. A wide range of concentrations (0.1−300 mg/mL) is investigated using a number of analytical methods such as fluorescence correlation spectroscopy (FCS), turbidimetry, dynamic light scattering (DLS), small-angle neutron scattering (SANS), and neutron spin-echo spectroscopy (NSE). The critical micelle concentration is determined using FCS to be 1 μM or less. The collapse of the micelles at the LCST is investigated using turbidimetry and DLS and shows a weak dependence on the degree of polymerization of the PNIPAM block. SANS with contrast matching allows us to reveal the core−shell structure of the micelles as well as their correlation as a function of temperature. The segmental dynamics of the PNIPAM shell are studied as a function of temperature and are found to be faster in the collapsed state than in the swollen state. The mode detected has a linear dispersion in q 2 and is found to be faster in the collapsed state as compared to the swollen state. We attribute this result to the averaging over mobile and immobilized segments.

A specially designed carbon nanotube (CNT) is developed for use in the early detection and treatment of cancer. The key functionalities for biomedical diagnosis and drug delivery are incorporated into the CNTs. In vivo imaging of live mice is achieved by intravenously injecting quantum dot (QD)‐conjugated CNT for the first time. With near infrared emission around 752 nm, the CNT with surface‐conjugated QD (CNT‐QD) exhibit a strong luminescence for non‐invasive optical in vivo imaging. CNT surface modification is achieved by a plasma polymerization approach that deposited ultra‐thin acrylic acid or poly(lactic‐co‐glycolic acid) (PLGA) films (∼3 nm) onto the nanotubes. The anticancer agent paclitaxel is loaded at 112.5 ± 5.8 µg mg−1 to PLGA‐coated CNT. Cytotoxicity of this novel drug delivery system is evaluated in vitro using PC‐3MM2 human prostate carcinoma cells and quantified by the 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide (MTT) assay. The in vivo distribution determined by inductively coupled plasma mass spectrometry (ICP‐MS) indicates CNT‐QD uptake in various organs of live animals.

In this work, we used co-sputtering of noble metals together with polytetrafluorethylene (PTFE) as a method for producing antibacterial metal/polymer nanocomposite coatings, where the precious metals are only incorporated in a thin surface layer. Moreover, they are finely dispersed as nanoparticles, thus saving additional material and providing a very large effective surface for metal ion release. Nanocomposite films with thickness between 100 and 300 nm were prepared with a wide range of metal filling between 10 and 40%. The antimicrobial effect of the nanocomposite coatings was evaluated by means of two different assays. The bactericidal activity due to silver release from the surface was determined by a modification of conventional disc diffusion methods. Inhibition of bacterial growth on the coated surface was investigated through a modified proliferation assay. Staphylococcus aureus and S. epidermidis were used as test bacteria, as these species commonly cause infections associated with medical polymer devices. The antibacterial efficiency of the coatings against different bacteria was demonstrated at extremely small noble metal consumption: Au: ∼1 mg m−2 and Ag: ∼0.1 g m−2. The maximum ability for having an antibacterial effect was shown by the Ag–Au/PTFE nanocomposite, followed by the Ag/PTFE nanocomposite.

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Head-related transfer functions (HRTFs) for human subjects in anechoic space were modeled with modified phase spectra, including minimum-phase-plus-delay, linear-phase, and reversed-phase-plus-delay functions. The overall (wide-band) interaural time delay (ITD) for the modeled HRTFs was made consistent with that of the empirical HRTFs by setting the position-dependent, frequency-independent delay in the HRTF for the lagging ear. Signal analysis of the minimum-phase-plus-delay reconstructions indicated that model HRTFs deviate from empirical HRTF measurements maximally for contralateral azimuths and low elevations. Subjects assessed the perceptual validity of the model HRTFs in a four-interval, two-alternative, forced-choice discrimination paradigm. Results indicate that monaural discrimination performance of subjects was at chance for all three types of HRTF models. Binaural discrimination performance was at chance for the linear-phase HRTFs, was above chance for some locations for the minimum-phase-plus-delay HRTFs, and was above chance for all tested locations for the reversed-phase-plus-delay HRTFs. An analysis of low-frequency timing information showed that all of these results are consistent with efficient use of interaural time differences in the low-frequency components of the stimulus waveforms. It is concluded that listeners are insensitive to HRTF phase spectra as long as the overall ITD of the low-frequency components does not provide a reliable cue. In particular, the minimum-phase-plus-delay approximation to the HRTF phase spectrum is an adequate approximation as long as the low-frequency ITD is appropriate. These results and conclusions are all limited to the anechoic case when the HRTFs correspond to brief impulse responses limited to a few milliseconds.