Inelastic Neutron Scattering Studies of First Order Phase Transitions in bcc Solid 4He

We report inelastic neutron scattering studies of the [110] transverse phonon branches of bcc ⁴He near the bcc-hcp transitions on the solid-liquid coexistence line and near the melting transition. The question behind the experiment was whether these transitions in a quantum solid are in any way different from what one observes in usual materials. In contrast to large softening of the T₁ branch seen near the bcc-hcp transition in group IV metals, we found that the transverse phonons in bcc ⁴He do not soften at all. Altough visual studies of the crystals near the transition are consistent with a martensitic transformation, neutron scattering indicates that the transition in solid ⁴He is different than in metals. Thus, the mechanism of the bcc-hcp transition remains an open question. Similar study done near the melting transition indicates that none of the phonons measured in the present experiment is affected by melting, which rules out a mechanical instability of the bulk as a mechanism of melting. Finally, in addition to the phonons, we observed a new feature at q=0 and at an energy transfer of 1.23meV which we attribute to neutron scattering by point defects. Similarly to the phonons, this feature did not change near any of the phase transitions.     

Controlling large-scale film morphology by phase manipulation in interference lithography

An experimental arrangement is described where a Babinet-Soleil compensator is inserted into the path of one of the three beams used for noncoplanar beam interference lithography. This birefringent element can change the phase of the beam so that either a positive two-dimensional pattern or an inverselike structure is generated in a photoresist without disturbing the mechanical geometry of the setup. Simulations are presented that confirm the validity of this approach. Large defect-free sample areas (>1 cm(2)) with submicrometer periodic patterns were obtained by expanding the laser beams used in the lithography experiment.     

Carbohydrate deficient glycoprotein syndrome type I: a cause of cerebellar vermis hypoplasia

To determine element contents of auditory ossicles, the malleus and incus were removed from 27 subjects which died at the ages between 40 and 98 years old, and their elemental contents were analyzed by inductively coupled plasma atomic emission spectrometry. It was found that the relative contents (RCs) of calcium and phosphorus were very high in the malleus and incus. The RCs of calcium and phosphorus in the ossicles corresponded to one-and-a-half-fold amounts as compared with the spongy bone of human cervical vertebrae. The mass ratio of calcium per phosphorus in the ossicles was almost the same as that of crystalline calcium phosphate hydroxyapatite. Relationships between the aging and RCs of minerals and between both the sexes in the ossicle were examined. It was found that both the RCs of calcium and phosphorus in the malleus and incus were really constant at the age over 40 years old, and that there was no significant difference of the mineral contents between men and women.     

Repetition rate enhancement and mode shaping in dual-cavity stretched pulse fiber laser

A novel orthogonally polarized coupled-cavities configuration for stretched pulse fiber lasers, based on tunable birefringence, is presented. By alignment of the birefringence, we achieve envelope modulated mode patterns, which in turn are used to increase the repetition rate of the laser while maintaining the well-profiled femtosecond pulses. Experimental results and a supporting theoretical model are presented.     

Inference of hidden variables in systems of differential equations with genetic programming

The data-driven modeling of dynamical systems is an important scientific activity, and many studies have applied genetic programming (GP) to the task of automatically constructing such models in the form of systems of ordinary differential equations (ODEs). These previous studies assumed that data measurements were available for all variables in the system, whereas in real-world settings, it is typically the case that one or more variables are unmeasured or “hidden.” Here, we investigate the prospect of automatically constructing ODE models of dynamical systems from time series data with GP in the presence of hidden variables. Several examples with both synthetic and physical systems demonstrate the unique challenges of this problem and the circumstances under which it is possible to reverse-engineer both the form and parameters of ODE models with hidden variables.     

The complex method applied to optimal truss configuration

The Complex Method of Box is applied to the determination of optimal member sizes and geometric configuration for minimum weight of 3-dimensional truss structures. Design constraints include bounds on member size, joint coordinates, member stresses, Euler buckling and joint displacements. The displacement method of structural analysis is used and the system is assumed to be linearly elastic. Statically indeterminate structures under multiple loading conditions can be optimized and the sizing as well as the geometric design variables may be linked. Limited topological changes are permitted for designs which have small member forces.The design spaces for sizing and geometric variables are separated. Geometry is modified by the Complex Method and member sizes by stress ratio and a scaling procedure for stiffness.The method is applied to two numerical examples from the literature. Results indicate favourable design improvements and rates of convergence. Substantial additional improvement resulting from member deletion is demonstrated.