Two-dimensional surrogate Hamiltonian investigation of laser-induced desorption of NO/NiO(100)

The photodesorption of NO from NiO(100) is studied from first principles, with electronic relaxation treated by the use of the surrogate Hamiltonian approach. Two nuclear degrees of freedom of the adsorbate-substrate system are taken into account. To perform the quantum dynamical wave-packet calculations, a massively parallel implementation with a one-dimensional data decomposition had to be introduced. The calculated desorption probabilities and velocity distributions are in qualitative agreement with experimental data. The results are compared to those of stochastic wave-packet calculations where a sufficiently large number of quantum trajectories is propagated within a jumping wave-packet scenario.     

Characterizing the topography of membrane receptors and signaling molecules from spatial patterns obtained using nanometer-scale electron-dense probes and electron microscopy

The flow of information through a cell requires the constant remodeling of cell signaling networks. Thus, spatially and temporally resolved microscopy of signaling components is needed to understand the behavior of normal cells as well as to uncover abnormal behavior leading to human disease. Nanoprobe labeling and transmission electron microscopy of cytoplasmic face-up sheets of cell membrane have been developed as a high-resolution approach to map the interactions of proteins and lipid during cell signaling. Membrane sheets are labeled with 3-15 nm electron-dense probes for receptors, signaling proteins and lipids and micrographs record the distributions of the probes relative to each other and to surface features. Here, we establish computational methods to extract spatial coordinates of probes from micrographs, to analyze and statistically validate the clustering and co-clustering of these probes and to integrate results between experiments in order to establish the relative spatial distributions of single and multiple probes. Our analyses, and the resulting programs for automating data collection and for carrying out statistical and clustering analyses provide toolboxes specialized for the spatiotemporal analysis and modeling of signal transduction pathways.     

Deterministic and storable single-photon source based on a quantum memory

A single-photon source is realized with a cold atomic ensemble (87Rb atoms). A single excitation, written in an atomic quantum memory by Raman scattering of a laser pulse, is retrieved deterministically as a single photon at a predetermined time. It is shown that the production rate of single photons can be enhanced considerably by a feedback circuit while the single-photon quality is conserved. Such a single-photon source is well suited for future large-scale realization of quantum communication and linear optical quantum computation.     

On the relation between cluster and classical tilting

Let be a triangulated category with a cluster tilting subcategory U. The quotient category is abelian; suppose that it has finite global dimension.We show that projection from to sends cluster tilting subcategories of to support tilting subcategories of , and that, in turn, support tilting subcategories of can be lifted uniquely to weak cluster tilting subcategories of .     

On the Elasticity of Generalized Arithmetical Congruence Monoids

Let a and b be positive integers with a ≤ b and ${a^2 \equiv a \, ({\rm mod} \, {b})}$ . The set ${M(a,b) = \{n \in \mathbb{N} | n \equiv a ({\rm mod} \, b)\} \cup \{1\}}$ is multiplicatively closed and known as an arithmetical congruence monoid (or ACM). It is well known that unique factorization need not occur in ACMs. In this paper, we investigate factorization results when we consider only elements of M(a, b) of sufficiently large size. More specifically, if M(a, b) is an ACM, we offer results concerning the elasticity of generalized ACMs (or GACMs) of the form ${M_r (a,b) = \{a +kb \in M(a,b) | k \geq r\} \cup \{1\}}$ where r is a nonnegative integer. We characterize when a generalized ACM is half-factorial (i.e. lengths of irreducible factorizations are constant). Moreover, we offer conditions, which force the elasticity to be infinite and derive a formula for finite elasticity in the case a ≠ 1.     

Synthesis,Thermal, and Optical Properties of Tris(5-aryl-1,3,4-oxadiazol-2-yl)-1,3,5-triazines,New Star-Shaped Fluorescent Discotic Liquid Crystals

The synthesis of tris(aryloxadiazolyl)triazines (TOTs), C₃-symmetrical star-shaped mesogenes with a 1,3,5-triazine center, 5-phenyl-1,3,4-oxadiazole arms, and various peripheral alkoxy side chains is reported. Threefold Huisgen reaction on a central triazine tricarboxylic acid and suitable aryltetrazoles yields the title compounds. Selected analogues with a benzene center are included in this study and allow for an evaluation of the impact of the central unit on the physical properties. Thermal (differential scanning calorimetry, DSC; polarization optical microscopy, POM), optical (UV/Vis, fluorescence), electric (time of flight, TOF), and structural (single crystal; wide-angle X-ray scattering, WAXS) properties of these compounds were investigated. The modification of alkoxy chain length and substitution pattern allows for a tuning of the physical properties. TOTs emit blue to yellow light, depending on conjugation length, donor–acceptor substitution, and solvent polarity, whereas concentration quenches and aggregation enhances the emission. The width of the mesophases is typically around ΔT=100–150 K but can even exceed 220 K. Polarization optical microscopy and X-ray diffraction on oriented filaments reveal that TOTs are highly ordered liquid crystals (LCs) with long-range hexagonal columnar structure.     

The effect of platinum electrode surfaces on precise primary pH measurements

Journal of Solid State Electrochemistry - For primary pH measurements, a platinum hydrogen electrode and a silver chloride electrode are immersed in the same solution in a cell without transference...     

Isolation of a Diylide‐Stabilized Stannylene and Germylene: Enhanced Donor Strength through Coplanar Lone Pair Alignment

The preparation of the first stable diylide‐substituted stannylene and germylene ( Y₂E, with E=Ge, Sn and Y=[PPh₃‐C‐SO₂Tol]^?) is reported. The synthesis is easily accomplished in one step from the sulfonyl‐substituted metalated ylide YNa and the corresponding ECl₂ precursors. Y₂Ge and Y₂Sn exhibit unusual structures in the solid state and in solution, in which the three adjacent lone pairs in the C‐E‐C linkage are arranged coplanar to each other. As shown by DFT studies, this bonding situation is preferred over the typical π‐donation from the ligands into the empty p‐orbital at the metal due to the strong anion‐stabilizing ability of the sulfonyl groups in the ylide backbone and their additional coordination to the metal. The alignment of the three lone pairs leads to a remarkable boost of the HOMO energy and thus of the donor strengths of the tetrylenes. Hence, Y₂Ge and Y₂Sn become stronger donors than their diamino or diaryl congeners and comparable to cyclic alkyl(amino)carbenes. First reactivity studies confirm the high reactivity of Y₂Ge and Y₂Sn , which for example undergo an intramolecular C?H activation reaction via metal–ligand cooperation.     

Polyfunctional Bis‐Lewis‐Acid‐/Bis‐Triazolium Catalysts for Stereoselective 1,4‐Additions of 2‐Oxindoles to Maleimides

Achieving enzyme‐like catalytic activity and stereoselectivity without the typically high substrate specificity of enzymes is a challenge in the development of artificial catalysts for asymmetric synthesis. Polyfunctional catalysts are considered to be a promising tool for achieving excellent catalytic efficiency. A polyfunctional catalyst system was developed, which incorporates two Lewis acidic/Brønsted basic cobalt centers in combination with triazolium moieties that are crucial for high reactivity and excellent stereoselectivity in the direct 1,4‐addition of oxindoles to maleimides. The catalyst is assembled through click chemistry and is readily recyclable through precipitation by making use of its charges. Kinetic studies support a cooperative mode of action. Diastereodivergency is achievable with either Boc‐protected or unprotected maleimide.