Optimized interactions for targeted self-assembly: application to a honeycomb lattice

We devise an inverse statistical-mechanical methodology to find optimized interaction potentials that lead spontaneously to a target many-particle configuration. Target structures can possess varying degrees of disorder, thus extending the traditional idea of self-assembly to incorporate both amorphous and crystalline structures as well as quasicrystals. For illustration purposes, our computational technique is applied to yield an optimized isotropic (nondirectional) pair potential that spontaneously yields the three-coordinated honeycomb lattice as the ground state structure in two dimensions. This target choice is motivated by its three-dimensional analog, the diamond lattice, which is known to possess desirable photonic band gap properties.     

Interface energy of semicoherent metal-ceramic interfaces

An ab initio based approach to determine energies and structures for semicoherent interfaces is developed and applied to the Fe(001)/VN(001) system. To account for elastic displacements resulting from the lattice misfit, we compare an atomistic approach using a model potential (embedded-atom method) with a continuum approach using the Peierls-Nabarro model. The total interface energy of the atomistic modeling is found to be well reproduced by the Peierls-Nabarro model, demonstrating that accurate interface energies of semicoherent interfaces can be obtained by combining first principles for the chemical part of the energy and a Peierls-Nabarro model to account for the elasticity of the media.     

Trapping of microparticles in the near field of an ultrasonic transducer

We are investigating means of handling microparticles in microfluidic systems, in particular localized acoustic trapping of microparticles in a flow-through device. Standing ultrasonic waves were generated across a microfluidic channel by ultrasonic microtransducers integrated in one of the channel walls. Particles in a fluid passing a transducer were drawn to pressure minima in the acoustic field, thereby being trapped and confined at the lateral position of the transducer. The spatial distribution of trapped particles was evaluated and compared with calculated acoustic intensity distributions. The particle trapping was found to be strongly affected by near field pressure variations due to diffraction effects associated with the finite sized transducer element. Since laterally confining radiation forces are proportional to gradients in the acoustic energy density, these near field pressure variations may be used to get strong trapping forces, thus increasing the lateral trapping efficiency of the device. In the experiments, particles were successfully trapped in linear fluid flow rates up to 1mm/s. It is anticipated that acoustic trapping using integrated transducers can be exploited in miniaturised total chemical analysis systems (microTAS), where e.g. microbeads with immobilised antibodies can be trapped in arrays and subjected to minute amounts of sample followed by a reaction, detected using fluorescence.     

Self assembly,structure and properties of the decanuclear lanthanide ring complex,Dy10(OC2H4OCH3)30

Self assembly produced high yields of the lanthanide ring complex Dy10(OC2H4OCH3)30, the largest lanthanide ring known, characterized by X-ray diffraction methods and by magnetic susceptibility as a function of temperature.     

First synthesis of etidronate partial amides starting from PCl3

Methods for the preparation of mixed tetra-amide esters 1 and 2, the partial amide ester 3, and tri- and P,P-diamides 4 and 5 from monophosphorus spieces 12, 8 and 9, respectively, were developed. Compounds 8 and 9 were obtained from phosphorus trichloride via MeOPCl2, which was treated with 2 eq. and 4 eq. of piperidine, followed by water or acetyl chloride, respectively. Tetrasubstituted amide bisphosphonates 1 and 2 were selectively dealkylated with lithium or silyl halide to achieve target compounds 3-5. Piperidine was found to be a good desilylation reagent. Quantum mechanical calculations illustrate why derivative 2 was produced in low yield. The usefulness of compounds 1, 3 and 4 as prodrugs of etidronate was determined in aqueous buffer and human serum.     

Nonadiabatic alignment of asymmetric top molecules: field-free alignment of iodobenzene

Nonadiabatic laser alignment of an asymmetric top molecule is studied using the combination of a quantum dynamical theory and time-resolved photofragment imaging experiments. In particular, the degree of alignment of iodobenzene, induced by an intense, linearly polarized picosecond laser pulse, is calculated and measured. Pronounced alignment is obtained under field-free conditions.     

Robustness of Objective and Subjective Speckle Patterns in the Speckle Strain Gauge

The robustness to rigid body object motions of three optical systems used in the speckle strain gauge were experimentally investigated and compared with analytical results of the correlation. It was found that an out-of-plane motion of the object damaged the reliability of the strain measure when recording the objective speckle patterns while subjective speckle patterns were more robust. Besides out-of-plane object motions, the robustness of a free-space geometry and an afocal imaging configuration are approximately the same, while a telecentric imaging system is more robust to rigid body motions but more sensitive to deformation gradients (basically in-plane rotation and tilt). Results from a measurement of the relaxation in a lead-tin alloy used in organ pipes is also presented.Presented at 1996 International Workshop on Interferometry (IWI ‘96), August 27-29, Wako, Saitama, Japan.     

Internal conversion coefficients of the transitions in Tm169

The conversion electron spectrum of Tm¹⁶⁹ has been measured by an iron-yoke double focusing spectrometer. Gamma-ray energies and gamma-ray intensities were measured by a bent crystal spectrometer. Conversion coefficients and conversion ratios were determined from the electron and gamma intensities. The conversion process of the retardedM 1 transitions of 177 keV and 198 keV was found to be normal, in agreement with our earlier directional correlation results. No penetration effects were found in the conversion process of the retarded 63 keVE1 transition.