Tandem ring-closing metathesis reaction with a ruthenium catalyst containing a N-heterocyclic ligand

The highly active catalyst 2 was used in tandem RCM to make molecules with various ring systems containing α,β-unsaturated carbonyl compounds

Photon-induced near-field electron microscopy (PINEM): theoretical and experimental

Electron imaging in space and time is achieved in microscopy with timed (near relativistic) electron packets of picometer wavelength coincident with light pulses of femtosecond duration. The photons (with an energy of a few electronvolts) are used to impulsively heat or excite the specimen so that the evolution of structures from their nonequilibrium state can be followed in real time. As such, and at relatively low fluences, there is no interaction between the electrons and the photons; certainly that is the case in vacuum because energy–momentum conservation is not possible. In the presence of nanostructures and at higher fluences, energy–momentum conservation is possible and the electron packet can either gain or lose light quanta. Recently, it was reported that, when only electrons with gained energy are filtered, near-field imaging enables the visualization of nanoscale particles and interfaces with enhanced contrast (Barwick et al 2009 Nature 462 902). To explore a variety of applications, it is important to express, through analytical formulation, the key parameters involved in this photon-induced near-field electron microscopy (PINEM) and to predict the associated phenomena of, e.g., forty-photon absorption by the electron packet. In this paper, we give an account of the theoretical and experimental results of PINEM. In particular, the time-dependent quantum solution for ultrafast electron packets in the nanostructure scattered electromagnetic (near) field is solved in the high kinetic energy limit to obtain the evolution of the incident electron packet into a superposition of discrete momentum wavelets. The characteristic length and time scales of the halo of electron–photon coupling are discussed in the framework of Rayleigh and Mie scatterings, providing the dependence of the PINEM effect on size, polarization, material and spatiotemporal localization. We also provide a simple classical description that is based on features of plasmonics. A major part of this paper is devoted to the comparisons between the theoretical results and the recently obtained experimental findings about the imaging of materials and biological systems

Structure of isolated biomolecules by electron diffraction-laser desorption: uracil and guanine

We report the structure of isolated biomolecules, uracil and guanine, demonstrating the capability of a newly developed electron diffraction apparatus augmented with surface-assisted IR laser desorption. This UED-4 apparatus provides a pulsed, dense molecular beam, which is stable for many hours and possibly days. From the diffraction patterns, it is evident that the plume composition is chemically pure, without detectable background from ions, fragmentation products, or molecular aggregates. The vibrational temperature deduced is indeed lower than the translational temperature of the plume indicating that the molecules are intact on such short time scales. The structures of uracil and guanine were refined at the deduced internal temperatures, and we compare the results with those predicted by density functional theory. Such experimental capability opens the door for many other studies of the structure (and dynamics) of biomolecules

Irreversible Chemical Reactions Visualized in Space and Time with 4D Electron Microscopy

We report direct visualization of irreversible chemical reactions in space and time with 4D electron microscopy. Specifically, transient structures are imaged following electron transfer in copper-tetracyanoquinodimethane [Cu(TCNQ)] crystals, and the oxidation/reduction process, which is irreversible, is elucidated using the single-shot operation mode of the microscope. We observed the fast, initial structural rearrangement due to Cu^+ reduction and the slower growth of metallic Cu^0 nanocrystals (Ostwald ripening) following initiation of the reaction with a pulse of visible light. The mechanism involves electron transfer from TCNQ anion-radical to Cu^+, morphological changes, and thermally driven growth of discrete Cu^0 nanocrystals embedded in an amorphous carbon skeleton of TCNQ. This in situ visualization of structures during reactions should be extendable to other classes of reactive systems

Nanofriction Visualized in Space and Time by 4D Electron Microscopy

In this letter, we report a novel method of visualizing nanoscale friction in space and time using ultrafast electron microscopy (UEM). The methodology is demonstrated for a nanoscale movement of a single crystal beam on a thin amorphous membrane of silicon nitride. The movement results from the elongation of the crystal beam, which is initiated by a laser (clocking) pulse, and we examined two types of beams: those that are free of friction and the others which are fixed on the substrate. From observations of image change with time we are able to decipher the nature of microscopic friction at the solid−solid interface: smooth-sliding and periodic slip-stick friction. At the molecular and nanoscale level, and when a force parallel to the surface (expansion of the beam) is applied, the force of gravity as a (perpendicular) load cannot explain the observed friction. An additional effective load being 6 orders of magnitude larger than that due to gravity is attributed to Coulombic/van der Waals adhesion at the interface. For the case under study, metal−organic crystals, the gravitational force is on the order of piconewtons whereas the static friction force is 0.5 μN and dynamic friction is 0.4 μN; typical beam expansions are 50 nm/nJ for the free beam and 10 nm/nJ for the fixed beam. The method reported here should have applications for other materials, and for elucidating the origin of periodic and chaotic friction and their relevance to the efficacy of nano(micro)-scale devices

Dynamics of clustered opinions in complex networks

A simple model for simulating tug of war game as varying the player number in a team is discussed to identify the slow pace of fast change. This model shows that a large number of information sources leads slow change for the system. Also, we introduce an opinion diffusion model including the effect of a high degree of clustering. This model shows that the de facto standard and lock-in effect, well-known phenomena in economics and business management, can be explained by the network clusters.Comment: 11 pages, 2 figure

A survey of recent estimates of price elasticities of demand for transport

This paper reviews 70 estimates of the price elasticity of demand for many different transport modes and market situations. The paper presents figures separately for passenger and freight transport and include estimates of both own-price and mode choice elasticities. It also presents some elasticity estimates on demand for gasoline, together with selected cross-price elasticities. In addition, it includes a brief exposition on the different concepts of elasticity - compensated, uncompensated, price, cross-price and mode choice - and discusses the relations between them. This paper shows that, since transportation is a derived demand, it tends to be inelastic. Although the review is confined to estimates of price elasticities, it notes that quality variables are often more important than price, particularly in the air, motor freight, and container markets. Finally, most of the estimates relate to developed countries, reflecting the availabilty of data, research resources, and domicile of the researchers. The elasticity estimates are nevertheless thought to be relevant to developing countries as well. But since intermodal competition is generally less intense in developing countries, this tends to make transport demand more inelastic, although the lower income levels in such countries may partly offset this effect.Environmental Economics&Policies,Economic Theory&Research,Access to Markets,Markets and Market Access,Consumption

Follower-Force Experiments with Geometric Non-Linear Coupling for Analytical Validation

This study was a follow-up of a previous study where static deflection data of a joined-wing test article was collected from a series of experiments using a laser scanner and a laser tracker while the test articles were subjected to follower-forces. One of the goals of this study was to collect accurate experimental data which could be used to validate analytical methods, such as geometrically exact beam theory, which are used to predict the nonlinear response of joined-wings. The load application system used on the previous study was not able to provide a follower-force on the test articles, and therefore the loads were not representative of what the joined-wing would experience under more realistic loading conditions. The test articles used for the experiments are the qualification model and the joined-wing model. The qualification model is simply a thin aluminum beam, which is 72 in long, 8 in wide, and 0.5 in thick, and the joined-wing model is made up of two aluminum beams, which are similar in dimension to the qualification model and are joined at the tip. The qualification model was used mainly for validating the experimental procedures in preparation for the actual experiment on the joined-wing model. The deflection data of the test articles were collected using a laser tracker, and some of the measurement locations were chosen for easy comparison with the results from the previous study. The experimental data is compared to the results obtained using finite element analysis to determine how close the finite element analysis predictions are to the actual data

Pattern Formation in a Two-Dimensional Array of Oscillators with Phase-Shifted Coupling

We investigate the dynamics of a two-dimensional array of oscillators with phase-shifted coupling. Each oscillator is allowed to interact with its neighbors within a finite radius. The system exhibits various patterns including squarelike pinwheels, (anti)spirals with phase-randomized cores, and antiferro patterns embedded in (anti)spirals. We consider the symmetry properties of the system to explain the observed behaviors, and estimate the wavelengths of the patterns by linear analysis. Finally, we point out the implications of our work for biological neural networks