Improvement of luminescence efficiency and photostability in polymer thin films

The photodegradation mechanism and luminescence efficiency of a series of thin polymer films prepared under a variety of conditions was studied. The conjugated polymer, poly(m-phenylene-co-2,5-dioctoxy-p-phenylenevinylene) (PmPV), is shown by infra-red spectroscopy to degrade via the chain scission of the carbon double bond along the polymer backbone. This causes a reduction in conjugation length and a blue shift in its absorption and photoluminescence (PL) spectra. To reduce photodegradation effects, films were prepared using argon (Ar) gas and were investigated in air and an oxygen free environment. The initial PL intensity increased by over 70% for Ar treated films. The PL decay in air was bi-exponential in nature, with a sharp initial decay linked to atmospheric oxygen, and a longer second decay linked to oxygen embedded in the film. The increase in both PL efficiency and degradation lifetime, coupled with device encapsulation, should significantly improve the performance of electroluminescent devices.     

Superresolution in far-field imaging

We demonstrate the feasibility of achieving superresolved images by using Fourier-plane phase masks and image multiplication, which together create effective point-spread functions that are not positive definite and therefore cannot be created by any single Fourier plane mask in a linear system. Three different configurations were investigated, all of which gave a spatial resolution exceeding that corresponding to the full open aperture of the optical system. One price that must be paid for the superresolution is inefficient use of the light source.     

Quantitative elemental analysis for rhodium and palladium in minerals by time-of-flight resonance ionization mass spectrometry

Results are presented for the trace analysis of Pd and Rh by time-of-flight-resonance ionization mass spectrometry (TOF-RIMS). The spectrometer, developed at the Advanced Mineral Technology Laboratory (Ontario, Canada), is based on a commercial laser-induced mass analyzer with upgrades that include independent laser ablation and ionization sources and pulsed ion optics to minimize noise caused by primary ion formation. The schemes presented for Rh and particularly for Pd detection are simpler than others reported in the literature. The experimental laser fluences were found to be in reasonable agreement with theoretical estimates. The TOF-RIMS measurements were quantified on the basis of calibration curves derived using reference samples covering 3 orders of magnitude in concentration. Minimum detection limits of ~15 parts per billion were found for both metals, with a precision of ~ +/-15%. Samples from sulfide, iron oxide, and silicate minerals were also examined. The results are in excellent agreement with those obtained using dynamics secondary ion mass spectrometry.     

The damping of helicon waves in a tipped magnetic field

The damping of helicon waves in indium was measured under nonlocal conditions with a variable angle between the wave vectorq and the magnetic field. In contrast to the predictions of the free-electron theory, the damping was not a monotonic function of the angle and exhibits considerable structure, which is attributed to minima in the Landau damping for certain orientations of the magnetic field. Minima in the damping are to be expected for such field directions as give rise to cyclotron orbits having a substantial number of electron states with orbital velocities perpendicular toq. In simple situations the critical orientations of the magnetic field may be deduced from a given Fermi surface by a geometrical construction. The construction has been extended to indium, and the tipping angles found are in reasonable agreement with the experiment.Based on a thesis to be submitted to the Senate of the Technion, Israel Institute of Technology, in partial fulfillment of the requirements for D.Sc. degree.     

Medicaid managed care and community providers: new partnerships

Growing enrollment in managed care plans among Medicaid recipients represents a new market for these plans but presents challenges to those providers that traditionally have served this population. To continue serving Medicaid patients, community-based providers must develop contracts or other types of partnerships with Medicaid-contracting health plans. This paper reviews the challenges to such collaboration and discusses the practical issues that plans and community-based providers must resolve to develop productive working relationships. Keys to successful collaboration are identified. Ways in which federal and state governments can help the collaborative process are suggested.     

Growth of CdTel−x Sex by the LEC and bridgman techniques

Large-grain CdTe_l−x Se_x boules with X (nominal) = 0.05, 0.10 and 0.15 have been grown by the liquid-encapsulated Czochralski technique, using B₂O₃ as the encapsulant, and also by a modified Bridgman technique. An argon pressure of 20 atm was used in both techniques. Details of the growth apparatus and procedure are presented. The following characterization methods were used to compare crystals obtained by the two growth techniques: mass spectroscopic analysis, emission spectroscopic analysis, X-ray diffraction analysis, electron probe microanalysis, laser calorimetry at 10.6 μm and infrared transmission as a function of wavelength.     

Numerical simulations of roughening temperatures in a hexagonal van-der-Waals4He crystal

We have carried out numerical simulations to investigate roughening on⁴He crystal surfaces. Algorithms were constructed for an h.c.p. crystal, incorporating van-der-Waals interatomic interactions. The Wulff plot was calculated at 0 K. Also, by sectioning the crystal in several symmetry directions, roughening temperatures, T_R, have been calculated for these orientations using a lattice-gas model. In particular, these have been determined for thec, a ands facets, as well as for lower-symmetry facets which involve interactions between higher-than-nearest-neighbours. On one of these facets, we have observed the formation of anisotropic clusters below a certain critical temperature. The values for the high-symmetry facets are more precise but in broad agreement with those calculated by Touzani and Wortis¹ and do not agree particularly well with the observed values. We are therefore investigating quantum corrections to the calculations.     

Data smashing: uncovering lurking order in data

From automatic speech recognition to discovering unusual stars, underlying almost all automated discovery tasks is the ability to compare and contrast data streams with each other, to identify connections and spot outliers. Despite the prevalence of data, however, automated methods are not keeping pace. A key bottleneck is that most data comparison algorithms today rely on a human expert to specify what ‘features'' of the data are relevant for comparison. Here, we propose a new principle for estimating the similarity between the sources of arbitrary data streams, using neither domain knowledge nor learning. We demonstrate the application of this principle to the analysis of data from a number of real-world challenging problems, including the disambiguation of electro-encephalograph patterns pertaining to epileptic seizures, detection of anomalous cardiac activity from heart sound recordings and classification of astronomical objects from raw photometry. In all these cases and without access to any domain knowledge, we demonstrate performance on a par with the accuracy achieved by specialized algorithms and heuristics devised by domain experts. We suggest that data smashing principles may open the door to understanding increasingly complex observations, especially when experts do not know what to look for.     

Cranberry cocktail juice, cranberry concentrates, and proanthocyanidins reduce reovirus infectivity titers in African green monkey kidney epithelial cell cultures

Studies were performed to investigate the effect of several cranberry and grape juice extracts on the inhibition of reovirus infectivity following cell culture inoculation. Infectivity testing was performed utilizing cranberry juice extracts NutriCran-100 and NutriCran-90. At 5% extract concentrations, titers were reduced by ca. 50%. Cranberry cocktail juice caused an infectivity loss of ca. 10%. We ascribe these data to higher concentrations of proanthocyanidins (PACs) in the cranberry extracts. Further testing was performed utilizing purified high and low molecular weight cranberry PAC fractions (CB HMW and CB LMW, respectively), a cranberry flavonol glycoside (CB EToAc), cranberry anthocyanins (CB CA), and a grape PAC extract. Reovirus titers were reduced to undetectable levels at PAC concentrations < or =0.2%. CB CA had no effect on the inhibition of infectivity titers. Loss of infectivity titers was in the order: GP PAC>CB HMW>CB LMW>CB EToAc. Probe homogenization of CB HMW enhanced the extract to efficacy levels equal to that of grape PAC. Reovirus dsRNA segments were undetectable 96-h postcranberry cocktail juice pretreatment of MA-104 cell cultures. This study indicates an inhibition of reovirus infectivity titers by cranberry or grape juices or their purified PAC extracts. Viral inhibition probably occurs at the host cell surface.