Hexagonal spiral growth in the absence of a substrate

Experiments on the formation of spiraling hexagons (350 - 1000 nm in width) from a solution of nanoparticles are presented. Transmission electron microscopy images of the reaction products of chemically synthesized cadmium nanocrystals indicate that the birth of the hexagons proceeds without assistance from static screw or edge dislocatons, that is, they spiral without constraints provided by an underlying substrate. Instead, the apparent growth mechanism relies on what we believe is a dynamical dislocation identified as a dense aggregate of small nanocrystals that straddles the spiraling hexagon at the crystal surface. This nanocrystal bundle, which we term the "feeder", also appears to release nanocrystals into the spiral during the growth process.Comment: 4 pages, 5 figure

TDRSS telecommunications study, phase 2

Providing an extension to parametric analysis of the telecommunications support capability of the Tracking and Data Relay Satellite System (TDRSS), this phase considers candidate modulation waveforms which could meet the shuttle telecommunications requirements and also be compatible with the TDRSS single access S-band service. In addition, it considers the feasibility of modifying a single access S-band user transponder for operation with conventional STDN signals emanating from remotely located ground stations

Collecting Child Support: A History of Federal and State Initiatives

In this article we sketch an overview of the increasing federal involvement in the child-support area. Because the federal role has grown so dramatically over the past 25 years, family law practitioners need to understand the different federal programs and requirements that affect state management of child-support programs. While for many low-income parents state agencies handle child-support establishment and collection, the federalization of child support has practical implications when it comes to both establishing and enforcing child support. For example, as the time limits of the Personal Responsibility and Work Opportunity Reconciliation Act begin to have their effects, child support may become a supplement more and more needed by custodial parents. We begin this article with a brief history of the changing nature of federal involvement in child support-focusing on the origins of the federally mandated state child-support departments (“IV-D” agencies)-and then examine the development of mandatory child-support guidelines. We conclude with a listing of the implications of the federalization of child support for the family law practitioner

Collecting Child Support: A History of Federal and State Initiatives

In this article we sketch an overview of the increasing federal involvement in the child-support area. Because the federal role has grown so dramatically over the past 25 years, family law practitioners need to understand the different federal programs and requirements that affect state management of child-support programs. While for many low-income parents state agencies handle child-support establishment and collection, the federalization of child support has practical implications when it comes to both establishing and enforcing child support. For example, as the time limits of the Personal Responsibility and Work Opportunity Reconciliation Act begin to have their effects, child support may become a supplement more and more needed by custodial parents. We begin this article with a brief history of the changing nature of federal involvement in child support-focusing on the origins of the federally mandated state child-support departments (“IV-D” agencies)-and then examine the development of mandatory child-support guidelines. We conclude with a listing of the implications of the federalization of child support for the family law practitioner

Collecting Child Support: A History of Federal and State Initiatives

In this article we sketch an overview of the increasing federal involvement in the child-support area. Because the federal role has grown so dramatically over the past 25 years, family law practitioners need to understand the different federal programs and requirements that affect state management of child-support programs. While for many low-income parents state agencies handle child-support establishment and collection, the federalization of child support has practical implications when it comes to both establishing and enforcing child support. For example, as the time limits of the Personal Responsibility and Work Opportunity Reconciliation Act begin to have their effects, child support may become a supplement more and more needed by custodial parents. We begin this article with a brief history of the changing nature of federal involvement in child support-focusing on the origins of the federally mandated state child-support departments (“IV-D” agencies)-and then examine the development of mandatory child-support guidelines. We conclude with a listing of the implications of the federalization of child support for the family law practitioner

TDRSS telecommunications study. Phase 1: Final report

A parametric analysis of the telecommunications support capability of the Tracking and Data Relay Satellite System (TDRSS) was performed. Emphasis was placed on maximizing support capability provided to the user while minimizing impact on the user spacecraft. This study evaluates the present TDRSS configuration as presented in the TDRSS Definition Phase Study Report, December 1973 to determine potential changes for improving the overall performance. In addition, it provides specifications of the user transponder equipment to be used in the TDRSS

Magnetocaloric Studies of the Peak Effect in Nb

We report a magnetocaloric study of the peak effect and Bragg glass transition in a Nb single crystal. The thermomagnetic effects due to vortex flow into and out of the sample are measured. The magnetocaloric signature of the peak effect anomaly is identified. It is found that the peak effect disappears in magnetocaloric measurements at fields significantly higher than those reported in previous ac-susceptometry measurements. Investigation of the superconducting to normal transition reveals that the disappearance of the bulk peak effect is related to inhomogeneity broadening of the superconducting transition. The emerging picture also explains the concurrent disappearance of the peak effect and surface superconductivity, which was reported previously in the sample under investigation. Based on our findings we discuss the possibilities of multicriticality associated with the disappearance of the peak effect.Comment: 30 pages, 10 figure

Sivers and Boer-Mulders functions in Light-Cone Quark Models

Results for the naive-time-reversal-odd quark distributions in a light-cone quark model are presented. The final-state interaction effects are generated via single-gluon exchange mechanism. The formalism of light-cone wave functions is used to derive general expressions in terms of overlap of wave-function amplitudes describing the different orbital angular momentum components of the nucleon. In particular, the model predictions show a dominant contribution from S- and P-wave interference in the Sivers function and a significant contribution also from the interference of P and D waves in the Boer-Mulders function. The favourable comparison with existing phenomenological parametrizations motivates further applications to describe azimuthal asymmetries in hadronic reactions.Comment: references and explanations added; version to appear in Phys. Rev.

Plasticity of visual attention in Isha yoga meditation practitioners before and after a 3-month retreat.

Meditation has lately received considerable interest from cognitive neuroscience. Studies suggest that daily meditation leads to long lasting attentional and neuronal plasticity. We present changes related to the attentional systems before and after a 3 month intensive meditation retreat. We used three behavioral psychophysical tests - a Stroop task, an attentional blink task, and a global-local letter task-to assess the effect of Isha yoga meditation on attentional resource allocation. 82 Isha yoga practitioners were tested at the beginning and at the end of the retreat. Our results showed an increase in correct responses specific to incongruent stimuli in the Stroop task. Congruently, a positive correlation between previous meditation experience and accuracy to incongruent Stroop stimuli was also observed at baseline. We also observed a reduction of the attentional blink. Unexpectedly, a negative correlation between previous meditation experience and attentional blink performance at baseline was observed. Regarding spatial attention orientation as assessed using the global-local letter task, participants showed a bias toward local processing. Only slight differences in performance were found pre- vs. post- meditation retreat. Biasing toward the local stimuli in the global-local task and negative correlation of previous meditation experience with attentional blink performance is consistent with Isha practices being focused-attention practices. Given the relatively small effect sizes and the absence of a control group, our results do not allow clear support nor rejection of the hypothesis of meditation-driven neuronal plasticity in the attentional system for Isha yoga practice

Physical Structure of Planetary Nebulae. I. The Owl Nebula

The Owl Nebula is a triple-shell planetary nebula with the outermost shell being a faint bow-shaped halo. We have obtained deep narrow-band images and high-dispersion echelle spectra in the H-alpha, [O III], and [N II] emission lines to determine the physical structure of each shell in the nebula. These spatio-kinematic data allow us to rule out hydrodynamic models that can reproduce only the nebular morphology. Our analysis shows that the inner shell of the main nebula is slightly elongated with a bipolar cavity along its major axis, the outer nebula is a filled envelope co-expanding with the inner shell at 40 km/s, and the halo has been braked by the interstellar medium as the Owl Nebula moves through it. To explain the morphology and kinematics of the Owl Nebula, we suggest the following scenario for its formation and evolution. The early mass loss at the TP-AGB phase forms the halo, and the superwind at the end of the AGB phase forms the main nebula. The subsequent fast stellar wind compressed the superwind to form the inner shell and excavated an elongated cavity at the center, but has ceased in the past. At the current old age, the inner shell is backfilling the central cavity.Comment: 10 pages, 6 figures, 1 table, to appear in the Astronomical Journa