Capture dynamics and far-infrared response in photovoltaic quantum well intersubband photodetectors

Recent progress in photovoltaic quantum well intersubband photodetectors (QWIP) makes these devices suitable for high-performance imaging and heterodyne detection. We report on investigations concerning the basic physics of the transport mechanism, the dynamical behavior, and the further optimization of these structures. GaAs/AlAs/AlGaAs double-barrier QWIPS designed for 3-5 μm wavelength operation provide an interesting model system to study the dynamical aspects of the photovoltaic response. We find strong evidence that carrier transfer across the AlAs barriers mainly occurs due to Γ-X intervalley scattering, even for AlAs layer thicknesses of 1-2 nm. We also discuss experimental results on photovoltaic QWIPs operating in the 8-12 μm regime. In these structures, photovoltaic operation is achieved using a combination of single-barrier quantum wells with built-in space-charge fields. We report on a photovoltaic QWIP with a cutoff energy of 118 meV and a zero-bias detectivity of 2.5×10⁹ cm√Hz/W, which is only three times less than the detectivity of a photoconductive QWIP with the same cutoff energy.     

Total synthesis and mechanism of action of the antibiotic armeniaspirol A

Emerging antimicrobial resistance urges the discovery of antibiotics with unexplored, resistance-breaking mechanisms. Armeniaspirols represent a novel class of antibiotics with a unique spiro[4.4]non-8-ene scaffold and potent activities against Gram-positive pathogens. We report a concise total synthesis of (±) armeniaspirol A in six steps with a yield of 20.3% that includes the formation of the spirocycle through a copper-catalyzed radical cross-coupling reaction. In mechanistic biological experiments, armeniaspirol A exerted potent membrane depolarization, accounting for the pH-dependent antibiotic activity. Armeniaspirol A also disrupted the membrane potential and decreased oxygen consumption in mitochondria. In planar lipid bilayers and in unilamellar vesicles, armeniaspirol A transported protons across membranes in a protein-independent manner, demonstrating that armeniaspirol A acted as a protonophore. We provide evidence that this mechanism might account for the antibiotic activity of multiple chloropyrrole-containing natural products isolated from various origins that share a 4-acylphenol moiety coupled to chloropyrrole as a joint pharmacophore. We additionally describe an efflux-mediated mechanism of resistance against armeniaspirols.

The antibiotic armeniaspirol A depolarized bacterial and mammalian cell membranes through a protonophore activity, that accounts for its potent antibiotic effects. A total synthesis of (±) armeniaspirol A was achieved in six steps.     

Cyclothiazeno-Komplexe des Wolframs mit Phosphaniminatound tertiär-Butoxyliganden

Cyclothiazeno Complexes of Tungsten with Phosphoraneiminato and t-Butoxy Ligands The cyclothiazeno complex [WCl₃(N₃S₂)]₂ reacts with the silylated phosphaneimine Me₃SiNPPh₃ in THF solution forming the cyclothiazenophosphoraneiminato complex [Cl₂W(N₃S₂)(NPPh₃)]_n which forms green crystals of [Cl₂W(N₃S₂)(NPPh₃)(Py)] ( 1 ) when pyridine is added. The corresponding reaction with Me₃SiNPMe₃ leads to the methyl derivative which is analogous to 1 and which is obtained as dark green crystals along with the tetrakis(phosphoraneiminato) complex of the crystal composition [W(NPMe₃)₄]Cl₂ · 2 [Cl₂W(N₃S₂)(NPMe₃)(Py)] · 2 CH₂Cl₂ ( 2 ). According to the crystal structure analyses the phosphoraneiminato ligands NPR₃^– cause as a result of the short WN bonds of approximately 180 pm a strong trans influence on one of the WN bonds of the planar WN₃S₂ rings and alternatingly long SN bonds. With LiOCMe₃ [WCl₃(N₃S₂)]₂ reacts forming the centrosymmetrically dimeric cyclothiazeno alkoxy complex [(Me₃CO)₄W(N₃S₂)Li₂Cl]₂ ( 3 ) the ion ensemble of which is linked via the lithium and the chlorine atoms.     

Collocation discretization for an integral equation in ocean acoustics with depth‐dependent speed of sound

We analyze two collocation schemes for the Helmholtz equation with depth‐dependent sonic wave velocity, modeling time‐harmonic acoustic wave propagation in a three‐dimensional inhomogeneous ocean of finite height. Both discretization schemes are derived from a periodized version of the Lippmann‐Schwinger integral equation that equivalently describes the sound wave. The eigenfunctions of the corresponding periodized integral operator consist of trigonometric polynomials in the horizontal variables and eigenfunctions to some Sturm‐Liouville operator linked to the background profile of the sonic wave velocity in the vertical variable. Applying an interpolation projection onto a space spanned by finitely many of these eigenfunctions to either the unknown periodized wave field or the integral operator yields two different collocation schemes. A convergence estimate of Sloan [J. Approx. Theory, 39:97–117, 1983] on non‐polynomial interpolation allows to show converge of both schemes, together with algebraic convergence rates depending on the smoothness of the inhomogeneity and the source. Copyright © 2016 John Wiley & Sons, Ltd.