Single-photon emitting diode in silicon carbide

Electrically driven single-photon emitting devices have immediate applications in quantum cryptography, quantum computation and single-photon metrology. Mature device fabrication protocols and the recent observations of single defect systems with quantum functionalities make silicon carbide (SiC) an ideal material to build such devices. Here, we demonstrate the fabrication of bright single photon emitting diodes. The electrically driven emitters display fully polarized output, superior photon statistics (with a count rate of $>$300 kHz), and stability in both continuous and pulsed modes, all at room temperature. The atomic origin of the single photon source is proposed. These results provide a foundation for the large scale integration of single photon sources into a broad range of applications, such as quantum cryptography or linear optics quantum computing.Comment: Main: 10 pages, 6 figures. Supplementary Information: 6 pages, 6 figure

Peptide hairpins with strand segments containing α- and β-amino acid residues: Cross-strand aromatic interactions of facing Phe residues

The incporation of β-amino acid residues into the strand segments of designed β-hairpin leads to the formation of polar sheets, since in the case of β-peptide strands, all adjacent carbonyl groups point in one direction and the amide groups orient in the opposite direction. The conformational analysis of two designed peptide hairpins composed of α/β-hybrid segments are described: Boc-βLeu-βPhe-Val-D-Pro-Gly-βLeu-βPhe-Val-OMe (1) and Boc-βLeu-Phe-βVal-D-Pro-Gly-βLeu-Phe-βVal-OMe (2). A 500-MHz 1H-NMR (nuclear magnetic resonance) analysis in methanol supports a significant population of hairpin conformations in both peptides. Diagnostic nuclear Overhauser effects (NOEs) are observed in both cases. X-ray diffraction studies on single crystals of peptide 1 reveal a β-hairpin conformation in both the molecules, which constitute the crystallographic asymmetric unit. Three cross-strand hydrogen bonds and a nucleating type II′ β-turn at the D-Pro-Gly segment are observed in the two independent molecules. In peptide 1, the Phe residues at positions 2 and 7 occur at the nonhydrogen-bonding position, with the benzyl side chains pointing on opposite faces of the β-sheet. The observed aromatic centroid-to-centroid distances are 8.92 Å (molecule A) and 8.94 Å (molecule B). In peptide 2, the aromatic rings must occupy facing positions in antiparallel strands, in the NMR-derived structure. Peptide 1 yields a normal hairpin-like CD spectrum in methanol with a minimum at 224 nm. The CD spectrum of peptide 2 reveals a negative band at 234 nm and a positive band at 221 nm, suggestive of an exciton split doublet. Modeling of the facing Phe side chains at the hydrogen-bonding position of a canonical β-hairpin suggests that interring separation is 4.78 Å for the gauche+gauche- (g+g-) rotamer. A previously reported peptide β-hairpin composed of only α-amino acids, Boc-Leu-Phe-Val-D-Pro-Gly-Leu-Phe-Val-OMe also exhibited an anomalous far-UV (ultraviolet) CD (circular dichroism) spectrum, which was interpreted in terms of interactions between facing aromatic chromophores, Phe 2 and Phe

2-{[2,8-Bis(trifluoro­meth­yl)quinolin-4-yl](hy­droxy)meth­yl}piperidin-1-ium 3-amino-5-nitro­benzoate sesquihydrate

The asymmetric unit of the title salt solvate, C17H17F6N2O+·C7H5N2O4 −·1.5H2O, comprises a piperidin-1-ium cation, a 3-amino-5-nitro­benzoate anion, and three fractionally occupied [i.e. 0.414 (3), 0.627 (6) and 0.459 (5)] disordered water mol­ecules of solvation. The cation has an L shape with a C—C—C—C torsion angle of −102.9 (3)° for the atoms linking the quinolinyl group to the rest of the cation. In the anion, the carboxyl­ate and nitro groups are essentially coplanar with the benzene ring [O—C—C—C torsion angle = 179.7 (2)° and O—N—C—C torsion angle = −3.9 (3)°]. In the crystal, extensive O—H⋯O, O—H⋯F and N—H⋯·O hydrogen bonding leads to the formation of a layer in the ab plane

THE EFFECT OF EXOGENOUS FACTORS ON THERMAL POWER PLANT EFFICIENCY

This study focuses on the relationship between exogenous factors (that cannot be directly impacted by the actions of an economic agent) and combined heat and power (CHP) plant efficiency. As a measure of fuel utilization efficiency this paper proposes to use the Сoefficient of Fuel Utilization (CFU), which is the Russian equivalent of the Primary Energy Factor indicator. Climate conditions and fuel type were used as the exogenous factors in this article. Climate conditions were measured via climate zone proxies. The cause-effect relationships were analyzed using a linear regression model. The findings of the study showcase that the plants, which use natural gas as their primary fuel, show higher fuel utilization efficiency compared to coil plants. Climate conditions were also proven to be a statistically significant factor with plants situated in the third climate zone (mostly regions of the Central and North-Western federal districts) showing the highest average CFU of about 71%. The research shows that the exogenous factors account for close to 20% of CHP plant fuel utilization efficiency in Russia. The authors conclude that climate conditions and fuel type should be taken into account when constructing various energy efficiency models applicable to the Russian context

Limits on models of the ultrahigh energy cosmic rays based on topological defects

An erratum exists for this article. Please see the description link below for details.Using the propagation of ultrahigh energy nucleons, photons, and electrons in the universal radiation backgrounds, we obtain limits on the luminosity of topological defect scenarios for the origin of the highest energy cosmic rays. The limits are set as a function of the mass of the X particles emitted by the cosmic strings or other defects, the cosmological evolution of the topological defects, and the strength of the extragalactic magnetic fields. The existing data on the cosmic ray spectrum and on the isotropic 100 MeV gamma-ray background limit significantly the parameter space in which topological defects can generate the flux of the highest energy cosmic rays, and rule out models with the standard X-particle mass of 10¹⁶GeV and higher.R. J. Protheroe and Todor Stane