Comparisons of predicted steady-state levels in rooms with extended- and local-reaction bounding surfaces

A combined beam-tracing and transfer-matrix model for predicting steady-state sound-pressure levels in rooms with multilayer bounding surfaces was used to compare the effect of extended- and local-reaction surfaces, and the accuracy of the local-reaction approximation. Three rooms—an office, a corridor and a workshop—with one or more multilayer test surfaces were considered. The test surfaces were a single-glass panel, a double-drywall panel, a carpeted floor, a suspended-acoustical ceiling, a double-steel panel, and glass fibre on a hard backing. Each test surface was modeled as of extended or of local reaction. Sound-pressure levels were predicted and compared to determine the significance of the surface-reaction assumption. The main conclusions were that the difference between modeling a room surface as of extended or of local reaction is not significant when the surface is a single plate or a single layer of material (solid or porous) with a hard backing. The difference is significant when the surface consists of multilayers of solid or porous material and includes a layer of fluid with a large thickness relative to the other layers. The results are partially explained by considering the surface-reflection coefficients at the first-reflection angles.     

Distortion-free single point imaging of multi-layered composite sandwich panel structures

The results of a magnetic resonance imaging (MRI) investigation concerning the effects of an aluminum honeycomb sandwich panel on the B1 and B0 fields and on subsequent image quality are presented. Although the sandwich panel structure, representative of an aircraft composite material, distorts B0 and attenuates B1, distortion-free imaging is possible using single point (constant time) imaging techniques. A new expression is derived for the error caused by gradient field distortion due to the heterogeneous magnetic susceptibility within a sample and this error is shown not to cause geometric distortion in the image. The origin of the B0 distortion in the sample under investigation was also examined. The graphite-epoxy 'skin' of the panel is the principal source of the B0 distortion. Successful imaging of these structures sets the stage for the development of methods for detecting moisture ingress and degradation within composite sandwich structures.     

Simultaneous detection of ultraviolet and infrared radiation in a single GaN/GaAlN heterojunction

Results are presented for a dual-band detector that simultaneously detects UV radiation in the 250-360 nm and IR radiation in the 5-14 microm regions with near zero spectral cross talk. In this detector having separate UV- and IR-active regions with three contacts (one common contact for both regions) allows the separation of the UV and IR generated photocurrent components, identifying the relative strength of each component. This will be an important development in UV-IR dual-band applications such as fire-flame detection, solar astronomy, and military sensing, eliminating the difficulties of employing several individual detectors with separate electronics-cooling mechanisms.     

Synthesis and Electronic Properties of Novel 5,7-Diazapentacene Derivatives

A route to the synthesis of novel 5,7-diazapentacenes and some preliminary studies on their properties is reported. A single crystal X-ray diffraction study of the dihexyl derivative showed it had formed a dimer during the analysis. The materials possess lower lying frontier orbitals than pentacene and may have potential applications in organic electronic devices. This synthetic method may be applicable to the synthesis of other azaacenes.     

Synthesis of Highly Fluorinated Arene Complexes of [Rh(Chelating Phosphine)]+ Cations,and their use in Synthesis and Catalysis

The synthesis of rhodium complexes with weakly binding highly fluorinated benzene ligands is described: 1,2,3-F₃C₆H₃, 1,2,3,4-F₄C₆H₂ and 1,2,3,4,5-F₅C₆H are shown to bind with cationic [Rh(Cy₂P(CH₂)_xPCy₂)]⁺ fragments (x=1, 2). Their structures and reactivity with alkenes, and use in catalysis for promoting the Tishchenko reaction of a simple aldehyde, are demonstrated. Key to the synthesis of these complexes is the highly concentrated reaction conditions and use of the [Al{OC(CF₃)₃}₄]⁻ anion.     

A Phosphinine-Derived 1-Phospha-7-Bora-Norbornadiene: Frustrated Lewis Pair Type Activation of Triple Bonds

Salt metathesis of 1-methyl-2,4,6-triphenylphosphacyclohexadienyl lithium and chlorobis(pentafluorophenyl)borane affords a 1-phospha-7-bora-norbornadiene derivative 2 . The C≡N triple bonds of nitriles insert into the P−B bond of 2 with concomitant C−B bond cleavage, whereas the C≡C bonds of phenylacetylenes react with 2 to form λ⁴-phosphabarrelenes. Even though 2 must formally be regarded as a classical Lewis adduct, the C≡N and C≡C activation processes observed (and the mild conditions under which they occur) are reminiscent of the reactivity of frustrated Lewis pairs. Indeed, NMR and computational studies give insight into the mechanism of the reactions and reveal the labile nature of the phosphorus–boron bond in 2 , which is also suggested by detailed NMR spectroscopic studies on this compound. Nitrile insertion is thus preceded by ring opening of the bicycle of 2 through P−B bond splitting with a low energy barrier. By contrast, the reaction with alkynes involves formation of a reactive zwitterionic methylphosphininium borate intermediate, which readily undergoes alkyne 1,4-addition.     

Development of a Neutral Diketopyrrolopyrrole Phosphine Oxide for the Selective Bioimaging of Mitochondria at the Nanomolar Level

Development of novel bioimaging materials that exhibit organelle specific accumulation continues to be at the forefront of research interests and efforts. Among the various subcellular organelles, mitochondria, which are found in the cytoplasm of eukaryotic cells, are of particular interest in relation to their vital function. To date, most molecular probes that target mitochondria utilise delocalised lipophilic cations such as triphenylphosphonium and pyridinium. However, the use of such charged motifs is known to be detrimental to the working function of the mitochondrial transmembrane potential and there remains a strong case for development of neutral mitochondrial fluorescent probes. Herein, we demonstrate for the first time the exploitation of diketopyrrolopyrrole-based chemistries for the realisation of a neutral fluorescent probe that exhibits organelle specific accumulation within the mitochondria at the nanomolar level. The synthesised probe, which bears a neutral triphenylphosphine oxide moiety, exhibits a large Stokes shift and high fluorescence quantum yield in water, both highly sought-after properties in the development of bioimaging agents. In vitro studies reveal no interference with cell metabolism when tested for the human MCF7 breast cancer cell and nanomolar subcellular organelle colocalisation with commercially available mitochondrial staining agent Mitotracker Red. In light of its novelty, neutral structure and the preferential accumulation at nanomolar concentrations we anticipate this work to be of significant interest for the increasingly larger community devoted to the realisation of neutral mitochondrial selective systems and more widely to those engaged in the rational development of superior organic architectures in the biological field.