Isomeric state of 80Y and its role in the astrophysical rp-process

A careful investigation of the isomeric transition of the long-lived state at 228.5 keV excitation energy in ⁸⁰Y has been done. The HIGISOL facility at the Jyv?skyl? isochronous cyclotron has been used. We used the electron magnetic transporter to prepare an appropriate source and to measure the electron spectra in clean background conditions. The measured internal conversion coefficient α_K = 0.50±0.07 allows unambiguous 1^- identification for the 228.5 keV first excited isomeric state in ⁸⁰Y. With a “bare" half-life of 6.8±0.5 s found in this work, this state is strongly populated in the rp-process during X-ray bursts and has therefore to be taken into account in X-ray burst model calculations. However, because of the similarity of the β-decay half-lives of isomeric and ground states, we find a maximum reduction in the effective β-decay lifetime of ⁸⁰Y of only 17±2%. Our results pave the way for a future investigation of the impact of the isomeric state on the “effective" ⁸⁰Y proton capture rate. Received: 14 March 2001 / Accepted: 10 July 2001     

Vortex formation in quantum dots in high magnetic fields

We study electronic structures of two-dimensional quantum dots in high magnetic fields using the density-functional theory (DFT) and the exact diagonalization (ED). With increasing magnetic field, beyond the formation of the totally spin-polarized maximum density droplet (MDD) state, the DFT gives the ground-state total angular momentum as a continuous function with well-defined plateaus. The plateaus agree well with the magic angular momenta of the ED calculation. By constructing a conditional wave function from the Kohn–Sham states we show that vortices enter the quantum dot one-by-one at the transition to the state with the adjacent magic angular momentum. Vortices are also observed outside the high-density region of the quantum dot. These findings are compared to the ED results and we report a significant agreement. We also study interpretations and limitations of the density functional approach in these calculations.     

Spinneret geometry modulates the mechanical properties of man-made cellulose fibers

Cellulose - The production of cellulose-based textile fibers with high toughness is vital for extending the longevity and thus developing a sustainable textile industry by reducing the global...     

Photoabsorption spectra of boron nitride fullerenelike structures

Optical absorption spectra have been calculated for a series of boron nitride fullerenelike cage structures BnNn of sizes n=12-36. The method used is a real-time, real-space implementation of the time-dependent density-functional theory, involving the full time propagation of the time-dependent Kohn-Sham equations. The spectra are found to be a possible tool for distinguishing between different boron nitride fullerene species and isomers. The trends and differences in the spectra are found to be related to the general geometry of the molecules. Comparison between local-density and generalized-gradient approximations for electron exchange-correlation functionals shows that both of them produce essentially the same spectral characteristics.     

Phase-transition-like properties of double-beam optical tweezers

We report on double-beam optical tweezers that undergo previously unknown phase-transition-like behavior resulting in the formation of more optical traps than the number of beams used to create them. We classify the optical force fields which produce multiple traps for a double-beam system including the critical behavior. This effect is demonstrated experimentally in orthogonally polarized (noninterfering) dual-beam optical tweezers for a silica particle of 2.32 μm diameter. Phase transitions of multiple beam trapping systems have implications for hopping rates between traps and detection of forces between biomolecules using dual-beam optical tweezers. It is an example of a novel dynamic system with multiple states where force fields undergo a series of sign inversions as a function of parameters such as size and beam separation.     

Photoabsorption in sodium clusters on the basis of time-dependent density-functional theory

The photoabsorption spectra of a continuous series of Na(n) clusters (n相似文献   

Optical force field mapping in microdevices

We present a method for characterizing microscopic optical force fields. Two dimensional vector force maps are generated by measuring the optical force applied to a probe particle for a grid of particle positions. The method is used to map out the force field created by the beam from a lensed fiber inside a liquid filled microdevice. We find transverse gradient forces and axial scattering forces on the order of 2 pN per 10 mW laser power which are constant over a considerable axial range (>35 microm). These findings suggest future useful applications of lensed fibers for particle guiding/sorting. The propulsion of a small particle at a constant velocity of 200 microm s(-1) is shown.