Electrochemically enabled oxidative aromatization of pyrazolines

Pyrazoles are a very important structural motif widely found in pharmaceuticals and agrochemicals. An electrochemically enabled approach for the sustainable synthesis of pyrazoles via oxidative aromatization of pyrazolines is presented. Inexpensive sodium chloride is employed in a dual role as a redox mediator and supporting electrolyte in a biphasic system (aqueous/organic). The method is applicable to a broad scope and can be conducted in the simplest electrolysis set-up using carbon-based electrodes. Hence, the method allows for simple work-up strategies such as extraction and crystallization, which enables application of this green synthetic route on a technically relevant scale. This is underlined by demonstration of a multi-gram scale electrolysis without loss in yield

Continuous Wave THz System Based on an Electrically Tunable Monolithic Dual Wavelength Y-Branch DBR Diode Laser

We analyse the use of a tunable dual wavelength Y-branch DBR laser diode for THz applications. The laser generates electrically tunable THz difference frequencies in the range between 100 and 300 GHz. The optical beats are tuned via current injection into a micro-resistor heater integrated on top of one of the distributed Bragg reflector (DBR) section of the diode. The laser is integrated in a homodyne THz system employing fiber coupled ion-implanted LT-GaAs log spiral antennas. The applicability of the developed system in THz spectroscopy is demonstrated by evaluating the spectral resonances of a THz filter as well as in THz metrology in thickness determination of a polyethylene sample

Electrochemical synthesis of pyrazolines and pyrazoles via [3+2] dipolar cycloaddition

Pyrazolines and pyrazoles are common and important motifs of pharmaceutical agents and agrochemicals. Herein, the first electrochemical approach for their direct synthesis from easily accessible hydrazones and dipolarophiles up to decagram scale is presented. The application of a biphasic system (aqueous/organic) even allows for the conversion of highly sensitive alkenes, wherein inexpensive sodium iodide is employed in a dual role as supporting electrolyte and mediator. In addition, mechanistic insight into the reaction is given by the isolation of key step intermediates. The relevance of the presented reaction is underlined by the synthesis of commercial herbicide safener mefenpyr-diethyl in good yields

Absence of superconductivity in ultra-thin layers of FeSe synthesized on a topological insulator

The structural and electronic properties of FeSe ultra-thin layers on Bi$_{2}$Se$_{3}$ have been investigated with a combination of scanning tunneling microscopy and spectroscopy and angle-resolved photoemission spectroscopy. The FeSe multi-layers, which are predominantly 3-5 monolayers (ML) thick, exhibit a hole pocket-like electron band at \bar{\Gamma} and a dumbbell-like feature at \bar{M}, similar to multi-layers of FeSe on SrTiO$_{3}$. Moreover, the topological state of the Bi2Se3 is preserved beneath the FeSe layer, as indicated by a heavily \it{n}-doped Dirac cone. Low temperature STS does not exhibit a superconducting gap for any investigated thickness down to a temperature of 5 K

Graphene-passivated nickel as an efficient hole-injecting electrode for large area organic semiconductor devices

Efficient injection of charge from metal electrodes into semiconductors is of paramount importance to obtain high performance optoelectronic devices. The quality of the interface between the electrode and the semiconductor must, therefore, be carefully controlled. The case of organic semiconductors presents specific problems: ambient deposition techniques, such as solution processing, restrict the choice of electrodes to those not prone to oxidation, limiting potential applications. Additionally, damage to the semiconductor in sputter coating or high temperature thermal evaporation poses an obstacle to the use of many device-relevant metals as top electrodes in vertical metal–semiconductor–metal structures, making it preferable to use them as bottom electrodes. Here, we propose a possible solution to these problems by implementing graphene-passivated nickel as an air stable bottom electrode in vertical devices comprising organic semiconductors. We use these passivated layers as hole-injecting bottom electrodes, and we show that efficient charge injection can be achieved into standard organic semiconducting polymers, owing to an oxide free nickel/graphene/polymer interface. Crucially, we fabricate our electrodes with low roughness, which, in turn, allows us to produce large area devices (of the order of millimeter squares) without electrical shorts occurring. Our results make these graphene-passivated ferromagnetic electrodes a promising approach for large area organic optoelectronic and spintronic devices.We acknowledge funding from EPSRC (EP/P005152/1, EP/M005143/1). R.M. and K.N. acknowledges funding from the EPSRC Cambridge NanoDTC (Grant No. EP/G037221/1). J.A.-W. acknowledges the support of his Research Fellowship from the Royal Commission for the Exhibition of 1851, and Royal Society Dorothy Hodgkin Research Fellowship. R. S. W. acknowledges support from a CAMS-UK fellowship

Dietary niche partitioning between sympatric brown hares and rabbits

Coexistence of ecologically similar species is sustained by niche partitioning, a fundamental element of which is diet. Overlapping of resource requirements between sympatric species can create interspecific competitive or facilitative effects on the foraging behaviour of herbivores. Brown hares (Lepus europaeus) and European rabbits (Oryctolagus cuniculus) are similar in size, morphology, feeding type and occupy the same habitats, but direct evidence of competition for resources between them is lacking. Both species are widespread and simultaneously pests and species of conservation concern in different parts of their range. We investigated dietary overlap of brown hares and European rabbits in pastures in relation to pasture management and hare and rabbit abundance. Grasses were the predominant component in both hare and rabbit diets with high overlap of plant species. Both rabbits and hares showed some selectivity for particular plants with evidence of consistent selection for Phleum spp. and relative avoidance of Poa spp. However, differences in the smaller components of hare and rabbit diet resulted in significant differences in diet overall. There was no evidence that higher relative density of one species led to dietary shifts but pasture management affected the diet of both species. Nutritional composition of diets of both species also differed between cattle and sheep pastures with higher fibre, ash and fat in the former. Our data provide no evidence of competitive exclusion between rabbits and hares on the basis of diet, but suggest that the effects of livestock on their respective diets may influence indirect competition in favour of rabbits over hares

Quantum Noise and Polarization Fluctuations in Vertical Cavity Surface Emitting Lasers

We investigate the polarization fluctuations caused by quantum noise in quantum well vertical cavity surface emitting lasers (VCSELs). Langevin equations are derived on the basis of a generalized rate equation model in which the influence of competing gain-loss and frequency anisotropies is included. This reveals how the anisotropies and the quantum well confinement effects shape the correlations and the magnitude of fluctuations in ellipticity and in polarization direction. According to our results all parameters used in the rate equations may be obtained experimentally from precise time resolved measurements of the intensity and polarization fluctuations in the emitted laser light. To clarify the effects of anisotropies and of quantum well confinement on the laser process in VCSELs we therefore propose time resolved measurements of the polarization fluctuations in the laser light. In particular, such measurements allow to distinguish the effects of frequency anisotropy and of gain-loss anisotropy and would provide data on the spin relaxation rate in the quantum well structure during cw operation as well as representing a new way of experimentally determinig the linewidth enhancement factor alpha.Comment: 16 pages and 3 Figures, RevTex, to be published in Phys. Rev.