Sympathetic cooling in an optically trapped mixture of alkali and spin-singlet atoms

We report on the realization of a stable mixture of ultracold lithium and ytterbium atoms confined in a far-off-resonance optical dipole trap. We observe sympathetic cooling of 6Li by 174Yb and extract the s-wave scattering length magnitude |a(6Li-174Yb)|=(13±3)a0 from the rate of interspecies thermalization. Using forced evaporative cooling of 174Yb, we achieve reduction of the 6Li temperature to below the Fermi temperature, purely through interspecies sympathetic cooling.     

Continuous Flow Synthesis of Ketones from Carbon Dioxide and Organolithium or Grignard Reagents

We describe an efficient continuous flow synthesis of ketones from CO₂ and organolithium or Grignard reagents that exhibits significant advantages over conventional batch conditions in suppressing undesired symmetric ketone and tertiary alcohol byproducts. We observed an unprecedented solvent‐dependence of the organolithium reactivity, the key factor in governing selectivity during the flow process. A facile, telescoped three‐step–one‐flow process for the preparation of ketones in a modular fashion through the in‐line generation of organometallic reagents is also established.     

The edge intersection graphs of paths in a tree

The class of edge intersection graphs of a collection of paths in a tree (EPT graphs) is investigated, where two paths edge intersect if they share an edge. The cliques of an EPT graph are characterized and shown to have strong Helly number 4. From this it is demonstrated that the problem of finding a maximum clique of an EPT graph can be solved in polynomial time. It is shown that the strong perfect graph conjecture holds for EPT graphs. Further complexity results follow from the observation that every line graph is an EPT graph. The class of EPT graphs is equivalent to the class of fundamental cycle graphs.     

A New Class of Brittle Graphs

A graph G is perfectly orderable in the sense of Chvátal if there exists a linear order on the set of vertices of G such that no induced path with vertices a, b, c, d and edges ab, bc, cd has a < b and d < c. A perfectly orderable graph G is brittle if every induced subgraph of G contains a vertex which is either endpoint or midpoint of no induced path with three edges in G. We present a new class of brittle graphs by forbidden configurations.     

Self-assembled monolayers derived from a double-chained monothiol having chemically dissimilar chains

The structure and conformation of self-assembled monolayers (SAMs) derived from the adsorption of a specifically designed double-chained partially fluorinated thiol having the formula 12,12,13,13,14,14,15,15,16,16,17,17,18,18,19,19,19-heptadecafluoro -2-tetradecylnona-decane-1-thiol ( 2) onto the surface of evaporated gold were examined by ellipsometry, contact angle goniometry, polarization modulation infrared reflection-absorption spectroscopy (PM-IRRAS), and X-ray photoelectron spectroscopy (XPS). The results were compared to those of SAMs generated from normal hexadecanethiol ( 1) and a structurally related single-chained partially fluorinated thiol having the formula 12,12,13,13,14,14,15,15,16,16,17,17,18,18,19,19,19-heptadecafluorononadecane-1-thiol ( 3). Collectively, the studies demonstrate that the double-chained adsorbate 2 forms SAMs on gold in which the alkyl chains are less densely packed and less conformationally ordered than those in the SAMs derived from each of the single-chained adsorbates. Furthermore, the fluorocarbon moieties in the SAMs derived from 2 are more tilted from the surface normal than those in the SAMs derived from 3. The low values of contact angle hysteresis suggest, however, that the double-chained adsorbate 2 generates homogeneous monolayer films on the surface of gold.     

Generalized bi-circular projections on minimal ideals of operators

We characterize generalized bi-circular projections on a minimal norm ideal of operators in where is a separable infinite dimensional Hilbert space.

     

Total synthesis of pumiliotoxins 209F and 251D via late-stage, nickel-catalyzed epoxide-alkyne reductive cyclization

Pumiliotoxins 209F and 251D were synthesized using highly selective nickel-catalyzed epoxide-alkyne reductive cyclizations as the final step. The exocyclic (Z)-alkene found in the majority of the pumiliotoxins was formed stereospecifically and regioselectively, without the use of a directing group on the alkyne, and the epoxide underwent ring opening exclusively at the less hindered carbon to provide the requisite tertiary alcohol. The epoxides were prepared using diastereoselective addition of a sulfoxonium anion to a proline-derived methyl ketone.     

Nickel-catalyzed synthesis of acrylamides from alpha-olefins and isocyanates

[reaction: see text] The nickel(0)-catalyzed coupling of alpha-olefins and isocyanates proceeds in the presence of the N-heterocyclic carbene ligand IPr to provide alpha,beta-unsaturated amides. Carbon-carbon bond formation occurs preferentially at the 2-position of the olefin. The N-tert-butyl amide products can be converted to the corresponding primary amides under acidic conditions.     

Benchmarking of electro-optic monitors for femtosecond electron bunches

The longitudinal profiles of ultrashort relativistic electron bunches at the soft x-ray free-electron laser FLASH have been investigated using two single-shot detection schemes: an electro-optic (EO) detector measuring the Coulomb field of the bunch and a radio-frequency structure transforming the charge distribution into a transverse streak. A comparison permits an absolute calibration of the EO technique. EO signals as short as 60 fs (rms) have been observed, which is a new record in the EO detection of single electron bunches and close to the limit given by the EO material properties.     

A vehicle overtaking model of traffic dynamics

Mathematical models that describe the dynamical behavior of a group of vehicles as they move along a stretch of road are known as car following models. They attempt to model the interactions between individual vehicles where the behavior of each vehicle is dependent on the motion of the vehicle directly in front and overtaking is not permitted. In this paper, the traditional car following model is modified by removing this "no overtaking" restriction and its behavior is investigated for a group of vehicles traveling on a closed loop. The resulting model is described in terms of a set of coupled time delay differential equations, and these are solved numerically to analyze their post transient behavior under a periodic perturbation. The effect of varying both the time taken for the driver to respond to the behavior of the vehicle in front and the length of the closed loop is examined. For certain parameter choices, the post transient behavior is found to be chaotic, and in these cases the degree of chaos is estimated using the Grassberger-Procaccia dimension.