SUMS: synchronous undulator–monochromator scans at Synchrotron Soleil

A strategy for performing synchronous undulator–monochromator scans (SUMS) compatible with the control system of Synchrotron Soleil has been developed. The implementation of the acquisition scheme has required the development of an electronic interface between the undulator and the beamline. The characterization of delays and jitters in the synchronous movement of various motor axes has motivated the development of a new electronic synchronization scheme among various axes, including the case when one of the axes is electronically accessible in `read‐only' mode. A software prototype has been developed to allow the existing hard continuous software to work in user units. The complete strategy has been implemented and successfully tested at the TEMPO beamline.     

Dynamic load balance applied to particle transport in fluids

This work presents a parallel numerical strategy to transport Lagrangian particles in a fluid using a dynamic load balance strategy. Both fluid and particle solvers are parallel, with two levels of parallelism. The first level is based on a substructuring technique and uses message passing interface (MPI) as the communication library; the second level consists of OpenMP pragmas for loop parallelisation at the node level. When dealing with transient flows, there exist two main alternatives to address the coupling of these solvers. On the one hand, a single-code approach consists in solving the particle equations once the fluid solution has been obtained at the end of a time step, using the same instance of the same code. On the other hand, a multi-code approach enables one to overlap the transport of the particles with the next time-step solution of the fluid equations, and thus obtain asynchronism. In this case, different codes or two instances of the same code can be used. Both approaches will be presented. In addition, a dynamic load balancing library is used on the top of OpenMP pragmas in order to continuously exploit all the resources available at the node level, thus increasing the load balance and the efficiency of the parallelisation and uses the MPI.     

Total Synthesis and Biological Evaluation of the Cytotoxic Resin Glycosides Ipomoeassin A–F and Analogues

A multitasking C‐silylation strategy using the readily available compound 26 as a surrogate for cinnamic acid represents the key design element of a total synthesis of all known members of the ipomoeassin family of resin glyosides. This protecting group maneuver allows the unsaturated acids decorating the glucose subunit of the targets to be attached at an early phase of the synthesis, prevents their participation in the ruthenium‐catalyzed ring‐closing metathesis (RCM) used to form the macrocyclic ring, and protects them against reduction during the hydrogenation of the resulting cycloalkene over Wilkinson’s catalyst. As the C‐silyl group can be concomitantly removed with the O‐TBS substituent using tris(dimethylamino)sulfonium difluorotrimethylsilicate (TASF) in acetonitrile, no separate protecting group manipulations were necessary in the final stages, thus contributing to a favorable overall “economy of steps”. In addition to the naturally occurring ipomoeassins, a small set of synthetic analogues has also been prepared by “diverted total synthesis”. The cytotoxicity of these compounds was assayed with two different cancer cell lines. The recorded data confirm previous findings that the acylation‐ and oxygenation pattern of these amphiphilic glycoconjugates is highly correlated with their biological activity profile. Ipomoeassin F turned out to be the most promising member of the series, showing IC₅₀ values in the low nanomolar range.     

Supramolecular self-assembly on the B-Si(111)-(√3x√3) R30° surface: From single molecules to multicomponent networks

Understanding the physical and chemical processes in which local interactions lead to ordered structures is of particular relevance to the realization of supramolecular architectures on surfaces. While spectacular patterns have been demonstrated on metal surfaces, there have been fewer studies of the spontaneous organization of supramolecular networks on semiconductor surfaces, where the formation of covalent bonds between organics and adatoms usually hamper the diffusion of molecules and their subsequent interactions with each other. However, the saturation of the dangling bonds at a semiconductor surface is known to make them inert and offers a unique way for the engineering of molecular patterns on these surfaces. This review describes the physicochemical properties of the passivated B-Si(111)-(√3x√3) R30° surface, that enable the self-assembly of molecules into a rich variety of extended and regular structures on silicon. Particular attention is given to computational methods based on multi-scale simulations that allow to rationalize the relative contribution of the dispersion forces involved in the self-assembled networks observed with scanning tunneling microscopy. A summary of state of the art studies, where a fine tuning of the molecular network topology has been achieved, sheds light on new frontiers for exploiting the construction of supramolecular structures on semiconductor surfaces.     

Single-chain magnet behavior in a finite linear hexanuclear molecule

The careful monitoring of crystallization conditions of a mixture made of a Tb^III building block and a substituted nitronyl-nitroxide that typically provides infinite coordination polymers (chains), affords a remarkably stable linear hexanuclear molecule made of six Tb^III ions and five NIT radicals. The hexanuclear units are double-bridged by water molecules but ab initio calculations demonstrate that this bridge is inefficient in mediating any magnetic interaction other than a small dipolar antiferromagnetic coupling. Surprisingly the hexanuclears, despite being finite molecules, show a single-chain magnet (SCM) behavior. This results in a magnetic hysteresis at low temperature whose coercive field is almost doubled when compared to the chains. We thus demonstrate that finite linear molecules can display SCM magnetic relaxation, which is a strong asset for molecular data storage purposes because 1D magnetic relaxation is more robust than the relaxation mechanisms observed in single-molecule magnets (SMMs) where under-barrier magnetic relaxation can operate.

A stable hexanuclear molecule made of a Tb^III building block and a substituted nitronyl-nitroxide radical show a single-chain magnet behavior despite being a finite molecule.     

meta-Substituted triphenylamines as new dyes displaying exceptionally large Stokes shifts

A straightforward synthesis of fluorescent tris-meta-substituted triphenylamines (m-TPAs) is presented. These new fluorophores display a unique feature that is a remarkably high Stokes shift up to 250 nm, as compared to their para counterparts. Although the meta substitution is made at the expense of the quantum yield, the latter is maintained at an appreciable level (5%) making the m-TPAs a new class of fluorophores adaptable to a large range of applications from biology to materials science.     

Homodyne detection readout for bit-oriented holographic memories

Homodyne detection is proposed to increase the readout signal of bit-oriented holographic memories. It can be easily implemented on present memory architectures by making the diffracted signal interfere with a reflection of the reading beam. The large resulting increase of the readout signal can be used to enhance the data transfer rate. A first experimental demonstration of such a readout procedure is presented.     

Simultaneous achievement of narrow pulse width and low pulse-to-pulse timing jitter in 1.3 microm passively mode-locked quantum-dot lasers

We have analyzed pulse width and timing jitter in passively mode-locked two-section InAs quantum-dot lasers emitting at 1310 nm and have identified two distinct, extensive mode-locked regions with robust short pulses and low timing jitter. A record combination of 2 ps pulses and 25 fs/cycle timing jitter (500 fs, 1-100 MHz), with 1 mW average output power per facet, is demonstrated.