Index matching in multilayered organic waveguides.

Index matching of guided modes in birefringent multilayered organic waveguides opens new prospects for the design of mode coupling and mode switching devices. We demonstrate index matching of guided modes in two multilayered structures, in (a) a PTCDA-Alq3-PTCDA three-layer and (b) a PTCDA-Alq3 effective medium multilayer waveguide. The optical waveguides were grown on a Pyrex substrate by organic molecular beam deposition. The occurrence of index matching was investigated both experimentally by measuring the effective refractive index dispersion of transverse electric and magnetic modes using the m-line technique and theoretically by modelling the index dispersion with a transfer matrix algorithm.

Emission dynamics of hybrid plasmonic gold/organic GaN nanorods.

We studied the emission of bare and aluminum quinoline (Alq3)/gold coated wurtzite GaN nanorods by temperature- and intensity-dependent time-integrated and time-resolved photoluminescence (PL). The GaN nanorods of ∼1.5 µm length and ∼250 nm diameter were grown by plasma-assisted molecular beam epitaxy. Gold/Alq3 coated GaN nanorods were synthesized by organic molecular beam deposition. The near band-edge and donor-acceptor pair luminescence was investigated in bare GaN nanorods and compared with multilevel model calculations providing the dynamical parameters for electron-hole pairs, excitons, impurity bound excitons, donors and acceptors. Subsequently, the influence of a 10 nm gold coating without and with an Alq3 spacer layer was studied and the experimental results were analyzed with the multilevel model. Without a spacer layer, a significant PL quenching and lifetime reduction of the near band-edge emission is found. The behavior is attributed to surface band-bending and Förster energy transfer from excitons to surface plasmons in the gold layer. Inserting a 5 nm Alq3 spacer layer reduces the PL quenching and lifetime reduction which is consistent with a reduced band-bending and Förster energy transfer. Increasing the spacer layer to 30 nm results in lifetimes which are similar to uncoated structures, showing a significantly decreased influence of the gold coating on the excitonic dynamics.

Controlling the exciton emission of gold coated GaAs-AlGaAs core-shell nanowires with an organic spacer layer.

Excitons are the most prominent optical excitations and controlling their emission is an important step towards new optical devices. We have investigated the exciton emission from uncoated and gold/aluminum quinoline (Alq3) coated GaAs-AlGaAs-GaAs core-shell nanowires (NWs) using temperature-, intensity- and polarization dependent photoluminescence (PL). Plasmonic GaAs-AlGaAs-GaAs NWs with a ∼10 nm thick Au coating but without an Alq3 spacer layer reveal a significant reduction of the PL intensity of the exciton emission compared with the uncoated NW sample. Plasmonic NW samples with the same nominal Au coverage and an additional Alq3 interlayer of 3 or 6 nm thickness show a clearly stronger PL intensity which increases with rising Alq3 spacer thickness. Time-resolved (TR) PL measurements reveal an increase of the exciton decay rate by a factor of up to two with decreasing Alq3 spacer thickness suggesting the presence of Förster energy transfer from NW excitons to plasmon oscillations in the gold film. The weak change of the decay time, however, indicates that Förster energy-transfer is only partially responsible for the PL quenching in the gold coated NWs. The main reason for the reduction of the PL emission is attributed to a gold induced band-bending in the GaAs NW core which causes exciton dissociation. With increasing Alq3 spacer thickness the band-bending decreases leading to a reduction of the exciton dissociation and PL quenching. Our interpretation is supported by electron energy loss spectroscopy measurements which show a signal reduction and blue shift of defect (possibly EL2) transitions when gold particles are deposited on NWs compared with bare or Alq3 coated NWs.

Real-time contrast-enhanced holographic imaging using phase coherent photorefractive quantum wells.

We demonstrate wide-field real-time and depth-resolved contrast enhanced holographic imaging (CEHI) using the all-optical phase coherent photorefractive effect in ZnSe quantum wells. Moving objects are imaged at large depth-of-field by the local enhancement of a static reference hologram. The high refresh rate of the holographic films enables direct-to-video monitoring of floating glass beads and of living Paramecium and Euglena cells moving in water. Depth resolution is achieved by tilting the incident laser beam with respect to the normal of the cuvette. This creates double images of the objects, which are analyzed geometrically and with Fresnel diffraction theory. A two-color CEHI set-up further enables the visualization of a concealed 95 µm thick wire behind a thin layer of chicken skin.

Eliminating thermal effects in z-scan measurements of thin PTCDA films.

We investigate the two-photon absorption (TPA) and nonlinear refraction of a micrometer thick 3,4,9,10-perylentetracarboxyl-dianhydride (PTCDA) film using z-scans with tightly focused 100 fs laser pulses. The PTCDA film was grown by organic molecular beam deposition on a Pyrex substrate. To study the influence of sample heating, the pulse repetition rate was varied between 4 MHz and 50 kHz with an acousto-optic pulse selector. We find that thermal effects diminish for pulse repetition times longer than 5 and 0.75 µs when using a 10x or 20x microscope lens, respectively, resulting in a TPA coefficient of 6 cm/GW and a nonlinear refractive index of 1.2 x 10⁻¹³ cm²/W at a wavelength of 820 nm.

Differential passive and active biaxial mechanical behaviors of muscular and elastic arteries: basilar versus common carotid.

Cerebrovascular disease continues to be responsible for significant morbidity and mortality. There is, therefore, a pressing need to understand better the biomechanics of both intracranial arteries and the extracranial arteries that feed these vessels. We used a validated four-fiber family constitutive relation to model passive biaxial stress-stretch behaviors of basilar and common carotid arteries and we developed a new relation to model their active biaxial responses. These data and constitutive relations allow the first full comparison of circumferential and axial biomechanical behaviors between a muscular (basilar) and an elastic (carotid) artery from the same species. Our active model describes the responses by both types of vessels to four doses of the vasoconstrictor endothelin-1 (10(-10)M, 10(-9)M, 10(-8)M, and 10(-7)M) and predicts levels of smooth muscle cell activation associated with basal tone under specific in vitro testing conditions. These results advance our understanding of the biomechanics of intracranial and extracranial arteries, which is needed to understand better their differential responses to similar perturbations in hemodynamic loading.

Prospects for microbeam radiation therapy of brain tumours in children to reduce neurological sequelae.

Microbeam radiation therapy (MRT), a form of experimental radiosurgery of tumours using multiple parallel, planar, micrometres-wide, synchrotron-generated X-ray beams ('microbeams'), can safely deliver radiation doses to contiguous normal animal tissues that are much higher than the maximum doses tolerated by the same normal tissues of animals or patients from any standard millimetres-wide radiosurgical beam. An array of parallel microbeams, even in doses that cause little damage to radiosensitive developing tissues, for example, the chick chorioallantoic membrane, can inhibit growth or ablate some transplanted malignant tumours in rodents. The cerebella of 100 normal 20 to 38g suckling Sprague-Dawley rat pups and of 13 normal 5 to 12kg weanling Yorkshire piglets were irradiated with an array of parallel, synchrotron-wiggler-generated X-ray microbeams in doses overlapping the MRT-relevant range (about 50-600Gy) using the ID17 wiggler beamline tangential to the 6GeV electron synchrotron ring at the European Synchrotron Radiation Facility in Grenoble, France. Subsequent favourable development of most animals over at least 1 year suggests that MRT might be used to treat children's brain tumours with less risk to the development of the central nervous system than is presently the case when using wider beams.

Phase coherent photorefractivity in ZnSe single quantum wells.

We observe an efficient phase coherent photorefractive effect in ZnSe single quantum wells for ultrashort light pulses resonant to the excitonic transition. The effect is attributed to the formation of an electron grating in the quantum well induced by the interference of coherent excitons that preserve phase and polarization of the incident light fields. All characteristic features of the diffracted signal are explained and reproduced by numerical calculations that are based on the optical Bloch equations for a three-level system.

Intellectual outcome in children and adolescents with acute lymphoblastic leukaemia treated with chemotherapy alone: age- and sex-related differences.

One of the most relevant concerns in long-term survivors of paediatric acute lymphoblastic leukaemia (ALL) is the development of neuropsychological sequelae. The majority of the published studies report on patients treated with chemotherapy and prophylactic central nervous system (CNS) irradiation, little is known about the outcome of patients treated with chemotherapy-only regimens. Using the standardised clinical and neuropsychological instruments of the SPOG Late Effects Study, the intellectual performance of 132 paediatric ALL patients treated with chemotherapy only was compared to that of 100 control patients surviving from diverse non-CNS solid tumours. As a group, ALL and solid tumour survivors showed normal and comparable intellectual performances (mean global IQ 104.6 in both groups). The percentage of patients in the borderline range (global IQ between 70 and 85) was comparable and not higher as expected (10% cases and 13% controls, expected 16%). Only 2 (2%) of the former ALL and 1 (1%) of the solid tumour patients were in the range of mental retardation (global IQ<70). Former known risk factors described in children treated with prophylactic CNS irradiation, like a younger age at diagnosis of ALL and female gender, remained valid in chemotherapy-only treated patients. The abandonment of prophylactic CNS irradiation and its replacement by a more intensive systemic and intrathecal chemotherapy led to a reduction, but not the disappearance of late neuropsychological sequelae.

Survey of bottled drinking waters sold in Canada for chlorate, bromide, bromate, lead, cadmium and other trace elements.

Mineral, spring and other bottled drinking waters sold in Canada in the winter of 1995-96 were surveyed for chlorate, bromide, bromate, Cr(VI), Li, B, Al, Mn, Cu, Zn, Sr, Ba, Be, V, Cr, Co, Ni, As, Se, Mo, Ag, Cd, Sb, Tl, Pb, Na, K, Ca and Mg. Chlorate and bromide were determined by ion chromatography (IC) with conductivity detection, Cr(VI) by IC with colorimetric detection, bromate by solvent extraction and gas chromatography (GC), trace elements by inductively coupled plasma mass spectrometry (ICPMS), and Na, K, Ca and Mg by flame atomic absorption spectrometry (FAA). Most chemicals in the 199 samples analysed were well within national and international drinking water guidelines. World Health Organization and/or Canadian drinking water guidelines were exceeded for B (22 samples), Al (9), Cr (1), Mn (5), Ni (1), As (10), Se (24) and Pb (1). Bromate levels are reported for information purposes and are considered as the maximum concentrations in the samples. In three distilled water products, unexpectedly high concentrations of Cu (88-147 micro g l(-1)) and Ni (16-35 micro g l(-1)) were found, and a comparison of distilled and non-distilled waters from two of the brands suggested the likely cause to be contamination during the distillation process. Li concentration in one sample was at a therapeutic dose and could pose an overdose risk to individuals on Li medication.

Review of the methods of the US Environmental Protection Agency for bromate determination and validation of method 317.0 for disinfection by-product anions and low-level bromate.

In recent years several methods have been published by the United States Environmental Protection Agency (EPA) which specify bromate as a target analyte. The first of these was EPA Method 300.0. As technological improvements in ion chromatographic hardware have evolved and new detection techniques have been designed, method detection limits for bromate have been reduced and additional procedures have been written, including EPA Method 300.1, 321.8 and, most recently, EPA Method 317.0. An overview of the evolution of these bromate methods since 1989 is presented. The focus is specific to each of these respective procedures, highlighting method strengths, weaknesses, and addressing how these methods fit into EPA's regulatory agenda. In addition, performance data are presented detailing the joint EPA/American Society for Testing and Materials multilaboratory validation of EPA Method 317.0 for disinfection by-product anions and low-level bromate.

Collaborative study of EPA Method 317.0 for the determination of inorganic oxyhalide disinfection by-products in drinking water using ion chromatography with the addition of a postcolumn reagent for trace bromate analysis.

The development of the U.S. Environmental Protection Agency (EPA) Method 317.0 is initiated to provide a sufficiently sensitive and fundamental technique for the compliance monitoring of trace levels of bromate in drinking water. After a comparative evaluation of Method 317.0 and elimination of a chlorite interference, this method is tested by a collaborative study in order to determine the precision and bias of the method and evaluate its potential role as a future compliance-monitoring method for inorganic disinfection by-products (DBPs) and trace bromate. This technique provides a practical method for future compliance monitoring for all of the inorganic oxyhalide DBPs including trace concentrations of bromate.

Performance evaluation of a method for the determination of bromate in drinking water by ion chromatography (EPA method 317.0) and validation of EPA method 324.0.

The potential carcinogenic nature of bromate has prompted global regulatory agencies, and industrial and academic institutions to publish several methods for the analysis of bromate in both drinking and bottled waters. The United States Environmental Protection Agency (EPA) has reported two methods capable of detecting bromate at or below the promulgated maximum contaminant level of 10.0 microg/l. These methods are EPA Method 300.1 and 317.0. Method 300.1 has been promulgated by EPA for compliance monitoring of bromate under Stage 1 of the Disinfectants/Disinfection By-Products Rule. Due to its sensitivity, selectivity and simplicity, Method 317.0 has been drafted and evaluated for potential use as a future compliance monitoring method. This manuscript describes the performance evaluation work with Method 317.0 and efforts completed at EPA's Technical Support Center that improved the sensitivity of Method 317.0, leading to the development of EPA Method 324.0

Eliminating the chlorite interference in US Environmental Protection Agency Method 317.0 permits analysis of trace bromate levels in all drinking water matrices.

A post-column reagent (PCR) method for bromate analysis in drinking water with a method detection limit (MDL) and method reporting limit (MRL) of 0.1 and 0.5 microg/l, respectively, has been developed by the United States Environmental Protection Agency (EPA) for future publication as EPA Method 317.0. The PCR method provides comparable results to the EPA's Selective Anion Concentration (SAC) method used to support the laboratory analysis of Information Collection Rule (ICR) low-level bromate samples and offers a simple, rugged, direct injection method with potential to be utilized as a compliance monitoring technique for all inorganic Disinfectants/Disinfection By-Products (D/DBPs). It has superior sensitivity for bromate compared to EPA Method 300.1, which was promulgated as the compliance monitoring method for bromate under Stage 1 of the D/DBP rule. This paper addresses elimination of the chlorite interference that was previously reported in finished waters from public water systems (PWSs) that employ chlorine dioxide as the disinfectant. An evaluation of Method 317.0 for the analysis of bromate in commercial bottled waters is also reported.

Analysis of 500-ng/l levels of bromate in drinking water by direct-injection suppressed ion chromatography coupled with a single, pneumatically delivered post-column reagent.

In July 1997, the US Environmental Protection Agency (EPA) began sampling and analyzing drinking water matrices from US municipalities serving populations greater than 100,000 for low-level bromate (> 0.20 microgram/l) in support of the Information Collection Rule (ICR) using the selective anion concentration (SAC) method. In September 1997, EPA published Method 300.1 which lowered the Method 300.0 bromate method detection limit (MDL) from 20.0 to 1.4 micrograms/l. This paper describes the research conducted at the EPA's Technical Support Center laboratory investigating a single post-column reagent, o-dianisidine (ODA), which has been successfully coupled to EPA Method 300.1 to extend the MDL for bromate. Initial studies indicate that this method offers a MDL which approaches the EPA's SAC method with the added benefit of increased specificity, shortened analysis time and reduced sample preparation. The method provides excellent ruggedness and acceptable precision and accuracy with a bromate MDL in reagent water of 0.1 microgram/l, and a method reporting limit of 0.50 microgram/l.

Cisplatin therapy in childhood: renal follow up 3 years or more after treatment. Swiss Pediatric Oncology Group.

BACKGROUND: In childhood, cisplatin is an essential component of solid tumour therapy such as in neuroblastomas, germ cell tumours, bone tumours, liver tumours and brain tumours. The potential nephotoxicity of cisplatin is widely recognized, but little information is available on permanent sequelae. METHODS: Of the 500 children included in the Swiss Pediatric Oncology Group Late Effect Study, a group of 46 patients (27 males and 19 females) aged 5.7-28 years (median 14 years) surviving the above-mentioned solid tumours entered the present study. The patients were disease-free and off antineoplastic medication for at least 3 years. No recent gastrointestinal or urinary disturbances had occurred, and diets as well as appetites were normal. RESULTS: Blood pressure and plasma or urinary calcium and phosphate were similar in 17 patients treated with cisplatin (dose 142-717, median 400 mg/m2), in 19 patients without cisplatin and in 20 control subjects. A tendency (P<0.02) towards increased plasma creatinine (79 (69-89) micromol/l; median and interquartile range) and low plasma magnesium (0.80 (0.78-0.85) mmol/l) was noted in patients treated with cisplatin as compared with those without cisplatin (68 (58-80) micromol/l; 0.84 (0.79-0.90) mmol/l) and controls (71 (64 80) micromol/l; 0.83 (0.80-0.90) mmol/l). No correlation was noted between the dosage of cisplatin and circulating magnesium or creatinine. CONCLUSIONS: The study demonstrates that the permanent renal disturbances ((i) decreased renal function and (ii) hypomagnesaemia) noted after treatment with cisplatin during infancy or childhood are mild. Furthermore, the study does not demonstrate renal sequelae in patients with the same malignancies who had been treated without cisplatin.