Biomedical subjects

D Hanstorp

Publications and source records attributed to D Hanstorp.

11 recordsLinked to original sources

PubMed2004

Radiative lifetime of a bound excited state of Te-.

We report on the first experimental study of the lifetime of a bound excited state of a negative ion. A new experimental technique was developed and used to measure the radiative lifetime of the 5p(5) (2)P(1/2) level of Te-. The experiment was performed in a magnetic storage ring, where a laser beam was applied along one of the straight sections. In the experiment the population of the excited J=1/2 level was probed each time the Te- ions passed through the laser field. A decay curve was built up by sampling the population of the excited level of the Te- ions as a function of time after injection into the ring. A multiconfiguration Dirac-Hartree-Fock calculation was performed in conjunction with the experiment. The calculation yielded a radiative lifetime of 0.45 s, in excellent agreement with the measured value of 0.42(5) s.

Journal Article↗

PubMed2000

Spectrum of doubly excited states in the K- ion.

The energies and widths of doubly excited states of the K- ion in the vicinity of the K(5 2D,7 2S,5 2F) thresholds have been measured in high resolution using a sensitive collinear laser-ion beam apparatus. These transient states appeared as resonances in the partial cross section for photodetachment via the K(5 2S)+e(-)(epsilon(p)) channel. Series of two states below the 5 2D threshold and four states below the 5 2F threshold have been found. The relative widths of members of the series below the 5 2F threshold exhibit anomalous behavior, as predicted by a semiclassical model.

Journal Article↗

PubMed2000

Sorting out bacterial viability with optical tweezers.

We have developed a method, using laser, optical tweezers and direct microscopic analysis of reproductive potential and membrane integrity, to assess single-cell viability in a stationary-phase Escherichia coli population. It is demonstrated here that a reduction in cell integrity, determined by using the fluorescent nucleic acid stain propidium iodide, correlated well with a reduction in cell proliferating potential during the stationary-phase period studied. Moreover, the same cells that exhibited reduced integrity were found to be the ones that failed to divide upon nutrient addition. A small but significant number of the intact cells (496 of 7,466 [6.6%]) failed to replicate. In other words, we did not find evidence for the existence of a large population of intact but nonculturable cells during the stationary-phase period studied but it is clear that reproductive ability can be lost prior to the loss of membrane integrity. In addition, about 1% of the stationary-phase cells were able to divide only once upon nutrient addition, and in a few cases, only one of the two cells produced by division was able to divide a second time, indicating that localized cell deterioration, inherited by only one of the daughters, may occur. The usefulness of the optical trapping methodology in elucidating the mechanisms involved in stationary-phase-induced bacterial death and population heterogeneity is discussed.

Escherichia coli↗

PubMed1996