Progress in the pumping of gamma-ray laser

A gamma-ray laser would stimulate coherent emission of radiation at wavelengths below 1 Å from excited states of nuclei. However, the difficulties in realizing such a device were considered insurmountable when the first cycle of study ended in1981. Since then, research on the feasibility of a gamma-ray laser has taken on a completely new character. A nuclear analog of the ruby laser has been proposed and many of the component steps for pumping the nuclei have been demonstrated experimentally. A quantitative model based upon the new data and the concepts of this decade shows the gamma-ray laser to be feasible if some real isotope has its properties sufficiently close to the ideals. The greatest positive impact has come from the discovery of giant resonances for pumping nuclei with photons that greatly reduce the levels of input power needed. Most recently, attention has been focused upon efforts to demonstrate prelasing levels of fluorescence from simulation nuclides and actual gamma-ray laser candidates. Problems being addressed are the acquisition of macroscopic samples of the best nuclei for testing and the demonstration of appropriate instrumentation.     

Crystal Structure of 1-nitro-2-phenylcycloprop-2-enecarbonitrile

The synthesis and x-ray crystal structure of 1 -nitro-2-phenylcycloprop-2-enecarbonitrile [1] is reported. The C-NO₂ bond length in1 is similar to but slightly shorter than that reported for 1, 2-diphenyl-3-nitrocyclopropene (2). Unlike2, 1 shows no tendency to ionize to the corresponding cyclopropenium ion in solution. This result is further supported by ab initio calculations.     

The Dynamics of Cultural Influence Networks

This article investigates the behavior of cultural influence networks over time, using a computer simulation based on a formal model of cultural transmission in organizations. In the formal model, every organizational member exerts some cultural influence on, and is influenced by, every other member; these influence paths constitute a dense social network and the weights of paths (ties) vary throughout the network. Over time, each organizational member's enculturation level changes in response to influence from other members, and the influence weight of each path changes in relationship to the cultural similarity of the individuals connected by the path. Virtual experiments explore the configuration and evolution of the cultural influence network under varying demographic conditions and influence principles. Demographic effects are studied by varying organizational size, hiring selectivity and turnover rates. Two principles for determining initial influence path weights are examined, cohort-based influence and random influence. The simulations show that the cultural influence network evolves over time to a robust configuration, fluctuating around a stable dynamic equilibrium as individuals enter and leave the organization. As turnover rates rise, cohort-based influence strengthens the influence network and reduces network inequality. In this model, cohort-based influence processes promote cultural stability in organizations.     

N-doping and coalescence of carbon nanotubes: synthesis and electronic properties

Self-assembly pyrolytic routes to large arrays (<2.5 cm²) of aligned CN_x nanotubes (15–80 nm OD and <100 μm in length) are presented. The method involves the thermolysis of ferrocene/melamine mixtures (5:95) at 900–1000 °C in the presence of Ar. Electron energy loss spectroscopy (EELS) reveals that the N content varies from 2–10%, and can be bonded to C in two different fashions (double-bonded and triple-bonded nitrogen). The electronic densities of states (DOS) of these CN_x nanotubes, using scanning tunneling spectroscopy (STS), are presented. The doped nanotubes exhibit strong features in the conduction band close to the Fermi level (0.18 eV). Using tight-binding and ab initio calculations, we confirm that pyridine-like (double-bonded) N is responsible for introducing donor states close to the Fermi Level. These electron-rich structures are the first example of n-type nanotubes. Finally, it will be shown that moderate electron irradiation at 700–800 °C is capable of coalescing single-walled nanotubes (SWNTs). The process has also been studied using tight-binding molecular dynamics (TBMD). Vacancies induce the coalescence via a zipper-like mechanism, which has also been observed experimentally. These vacancies trigger the organization of atoms on the tube lattices within adjacent tubes. These results pave the way to the fabrication of nanotube heterojunctions, robust composites, contacts, nanocircuits and strong 3D composites using N-doped tubes as well as SWNTs. Received: 10 October 2001 / Accepted: 3 December 2001 / Published online: 4 March 2002     

Initial Search for Triggered Gamma Emission from 178Hfm2 Using the YSU Miniball Array

Experiments with the long-lived, high-K isomer ¹⁷⁸Hf^m2 have been recognized as intriguing tests of multi-quasiparticle state structures and their interactions with external radiation. A triggered release of the energy stored by this isomer, 2.5 MeV per nucleus or 1.2 GJ/gram, in the form of a gamma-ray burst might prove valuable for numerous applications. The observation of “accelerated” decay of ¹⁷⁸Hf^m2 during irradiation by 90-keV bremsstrahlung has already been reported, but with poor statistical accuracy due to the experimental approach. That approach employed single Ge detectors to seek increases in the areas of peaks at energies corresponding to transitions in the spontaneous decay of the isomer. The need for better quality data to confirm those results has motivated the development of improved detection concepts. One such concept was utilized here to perform an initial search for low-energy (<20 keV) triggered gamma emission from ¹⁷⁸Hf^m2 using the YSU miniball detector array. This revised version was published online in August 2006 with corrections to the Cover Date.     

Non-Radiative Triggering of Long-Lived Nuclear Isomers

The triggering of long-lived isomeric nuclei by non-radiative excitation to a relatively short-lived mediating state is considered. Coulomb triggering in inelastic scattering of heavy ions, a transfer of triggering energy from resonant electron transitions of atomic shell (NEET) and triggering by capture of a free electron into a bound atomic state (NEEC) are discussed. Cross sections for the above processes of non-radiative triggering are presented and the relative efficiencies of these different triggering mechanisms are discussed. Numerical estimates are presented for the selected isomers. This revised version was published online in August 2006 with corrections to the Cover Date.     

The educational needs and professional roles of Canadian physicians and nurses regarding genetic testing and adult onset hereditary disease

OBJECTIVE: To investigate the knowledge, professional involvement and confidence of Canadian nurses and physicians in providing genetic services for adult onset hereditary disease. METHODS: 1,425 physicians and 1,425 nurses received a mailed questionnaire with reminders. The response rates were 50% (n = 543) and 79% (n = 975), respectively. RESULTS: Forty-eight percent of physicians and 31% of nurses lacked formal education in genetics. Respondents reported being involved in caring for people at risk for adult onset hereditary disease. Their levels of confidence that they could perform tasks, such as counselling about predictive genetic tests, however, were lower than their levels of expectation that it would be important for them to provide these services. CONCLUSIONS: The expected roles and educational needs of Canadian nurses and physicians have broad areas of overlap suggesting the possibility of combined professional education programs and multiple ways of organizing teams to provide genetic services to people at risk for adult onset hereditary disease.     

Finite strain solutions in compressible isotropic elasticity

Three classes of compressible isotropic elastic solids are introduced, for each of which the strain energy, expressed as a function of the three principal invariants of the stretch tensors, is linear in two of its arguments and nonlinear in the third argument. One of these is the class of harmonic materials. Several deformation fields are examined, for which the governing equations, for general compressible isotropic elastic response, reduce to a nonlinear ordinary differential equation. For the three special classes of materials, this differential equation may be solved in closed form, giving a deformation field which is independent of the material response function, or its solution may be reduced to a single quadrature, involving the nonlinear material response function.     

Ruthenium-caged antisense morpholinos for regulating gene expression in zebrafish embryos

Photochemical approaches afford high spatiotemporal control over molecular structure and function, for broad applications in materials and biological science. Here, we present the first example of a visible light responsive ruthenium-based photolinker, Ru(bipyridine)₂(3-ethynylpyridine)₂ (RuBEP), which was reacted stoichiometrically with a 25mer DNA or morpholino (MO) oligonucleotide functionalized with 3′ and 5′ terminal azides, via Cu(i)-mediated [3+2] Huisgen cycloaddition reactions. RuBEP-caged circular morpholinos (Ru-MOs) targeting two early developmental zebrafish genes, chordin and notail, were synthesized and tested in vivo. One-cell-stage zebrafish embryos microinjected with Ru-MO and incubated in the dark for 24 h developed normally, consistent with caging, whereas irradiation at 450 nm dissociated one 3-ethynylpyridine ligand (Φ = 0.33) and uncaged the MO to achieve gene knockdown. As demonstrated, Ru photolinkers provide a versatile method for controlling structure and function of biopolymers.