Strain induced band gap deformation of H/F passivated graphene and h-BN sheet

Strain induced band gap deformations of hydrogenated/fluorinated graphene and hexagonal BN sheet have been investigated using first principles density functional calculations. Within harmonic approximation, the deformation is found to be higher for hydrogenated systems than for the fluorinated systems. Interestingly, our calculated band gap deformation for hydrogenated/fluorinated graphene and BN sheets are positive, while those for pristine graphene and BN sheet are found to be negative. This is due to the strong overlap between nearest neighbor {\pi} orbitals in the pristine sheets, that is absent in the passivated systems. We also estimate the intrinsic strength of these materials under harmonic uniaxial strain, and find that the in-plane stiffness of fluorinated and hydrogenated graphene are close, but larger in magnitude as compared to those of fluorinated and hydrogenated BN sheet.Comment: Submitted to PR

The Long Revolution of Radiocarbon as Seen throughthe History of Swiss Lake-Dwelling Research

In diesem Artikel soll die Anwendung der Radiokarbondatierung in der Archäologie neu untersucht werden, basierend auf ihrer Entwicklung während der Erforschung der Schweizer Seeufersiedlungen zwischen 1950 und 1970. Ziel ist es zu erklären, warum die Archäologen die durch diese Methode gewonnenen Resultate zunächst nicht akzeptieren konnten. Zwei Schlüsselfragen leiten die Untersuchung: Die erste fragt nach dem disziplinären Kontext, der die Rezeption von 14C unter Prähistorikern beeinflusste. Die zweite bezieht die methodologischen Aushandlungen über C14 und der damit verbundenen Methode der Dendrochronologie mit ein. Während sich C14 und Dendrochronologie seit den 1960er Jahren im Kalibrationsprozess ergänzten, lieferte die Dendrochronologie darüber hinaus Einzeldaten, die gerade im Bereich der Pfahlbauten mit ihrer guten Holzerhaltung der C14-Datierung rasch Konkurrenz machten. Tatsächlich hing diese Konkurrenz mit den unterschiedlichen Arten der Datengewinnung und Zeitmessung zu tun.This paper reassesses the implementation of radiocarbon dating in archaeology based on the technique’s development while researching ancient lake dwellings in Switzerland between 1950 and 1970. The aim is to explain archaeologists’initial failure to accept the results obtained by this method. Two key issues are thereby the core focus of this analysis. The first concerns the disciplinary context that influenced the reception of 14C dating among prehistorians. The second deals with methodological discussions concerning 14C dating and dendrochronology, being radiocarbon dating’s most related chronological tool. While dendrochronology and 14C were first complementary in the 14C calibration process since the 1960s, it was then quickly realized that dendrochronology produced more detailed temporal data due to the good preservation conditions of wooden structures at Swiss lake dwellings and thus competed with 14C results. In fact, this competition had to do with the two differing methodologies of data acquisition and time measurement

Combined aptamer and transcriptome sequencing of single cells.

The transcriptome and proteome encode distinct information that is important for characterizing heterogeneous biological systems. We demonstrate a method to simultaneously characterize the transcriptomes and proteomes of single cells at high throughput using aptamer probes and droplet-based single cell sequencing. With our method, we differentiate distinct cell types based on aptamer surface binding and gene expression patterns. Aptamers provide advantages over antibodies for single cell protein characterization, including rapid, in vitro, and high-purity generation via SELEX, and the ability to amplify and detect them with PCR and sequencing

Deterministic entanglement between a propagating photon and a singlet--triplet qubit in an optically active quantum dot molecule

Two-electron charged self-assembled quantum dot molecules exhibit a decoherence-avoiding singlet-triplet qubit subspace and an efficient spin-photon interface. We demonstrate quantum entanglement between emitted photons and the spin-qubit after the emission event. We measure the overlap with a fully entangled state to be $69.5\pm2.7\,\%$, exceeding the threshold of $50\,\%$ required to prove the non-separability of the density matrix of the system. The photonic qubit is encoded in two photon states with an energy difference larger than the timing resolution of existing detectors. We devise a novel heterodyne detection method, enabling projective measurements of such photonic color qubits along any direction on the Bloch sphere

A Molecular Approach to Well-defined Metal Sites Supported on Oxides with Oxidation State and Nuclearity Control

A molecular understanding of the catalytically active site is essential to rationally develop metal-containing heterogeneous catalysts. The controlled grafting of molecular precursors on pre-treated supports, often referred to as surface organometallic chemistry, is an approach to prepare well-defined heterogeneous catalysts with complex organic functionalities. However, many heterogeneous catalysts do not contain organic ligands coordinated to their active sites. To model such sites, the principles of surface organometallic chemistry therefore have to be adapted. Here, we describe a method, which provides access to molecularly-defined metal sites supported on oxides, which do not contain organic functionalities and are uniform in oxidation state and nuclearity. By consecutive grafting of suitable molecular precursors and controlled thermal treatment, we prepared and characterized well-defined dinuclear Cr(II) and Cr(III) species and mononuclear Cr(III) species supported on silica. We also investigated the polymerization activity of these materials in view of the well-known ethylene polymerization catalyst based on CrOx/SiO2, the so-called Phillips catalyst. This study led to new insights on the catalytically active sites in ethylene polymerization, which are based on Cr(III), not Cr(II)

Kinetic Studies of the Hydrolyses and Aminolyses of Phosphorus (V) Chlorides And Proton Transfer at Carbon

Phosphorus oxychloride (POCl3) and thiophosphoryl chloride (PSCl3) are useful phosphorylating reagents. However, they are usually used under dry conditions as their reactivity toward water has been perceived as a problem. As part of an on-going program to develop aqueous aminophosphorylation procedures, we have investigated the reactivities of phosphodichloridate and thiophosphodichloridate ions in aqueous solutions as more selective water-soluble alternatives to POCl3 and PSCl3. We report the pH-kobs profiles for the hydrolyses of phosphodichloridate and thiophosphodichloridate ions in aqueous solutions. Both species show broad pH-kobs plateaus that extend to high pHs. The aminolyses of phosphodichloridate and thiophosphodichloridate ions in aqueous amine solutions have also been followed. Good selectivity towards aminolysis over hydrolysis processes has been observed. We have applied our kinetic data towards the optimisation of aqueous aminophosphorylation procedures, which has led to near-quantitative conversion of amino-nucleosides to thiophosphoramidate products. Finally, an additional research project focused upon peri-dimethylamino substituent effects on proton transfer at carbon in α-naphthylacetate esters. Rate constants for the exchange of hydrogen for deuterium at the α-CH2 positions of naphthalen-1-yl-acetic acid tert-butyl ester and 8-(N,N-dimethylamino-naphthalen-1-yl)-acetic acid tert-butyl ester have been determined in potassium deuteroxide solutions

Questioning the existence of a unique ground state structure for Si clusters

Density functional and quantum Monte Carlo calculations challenge the existence of a unique ground state structure for certain Si clusters. For Si clusters with more than a dozen atoms the lowest ten isomers are close in energy and for some clusters entropic effects can change the energetic ordering of the configurations. Isotope pure configurations with rotational symmetry and symmetric configurations containing one additional isotope are disfavored by these effects. Comparisons with experiment are thus difficult since a mixture of configurations is to be expected at thermal equilibrium