Status of the LASER-IGISOL collaboration at the University of Jyväskylä

Recent laser spectroscopy studies at the IGISOL facility, University of Jyväskylä have focussed on the shape transition at N?=?60. A new technique of optical pumping in the ion beam cooler has given unique access to the radioactive isotopes of niobium and yttrium. Further spectroscopy from metastable states allowed nuclear moments and charge radii to be extracted for isotopes in the chains of Mo and Nb, thus exploring the extent of nuclear deformation across the entire Z?=?36–42 region.     

Double-layer-relevant laboratory results

Many double-layer-relevant laboratory experiments have been carried out at the University of Wisconsin. Laboratory stair-step double layers, which resemble three or more weak double layers joined in series, have been produced without ionization. Double-layer floating potential fluctuations have been investigated and progress has been made in developing a novel technique for measuring electron energy distribution functions in low-density double layers (i.e. λ_D ≫probe dimensions). A new inductive plasma source has been developed. With this source, magnetized double layers can be routinely produced. These magnetized double layers are often weak stair-step double layers that are oblique to the magnetic field. Laboratory data of emitting probe characteristics taken in tenuous plasmas have helped to quantify space-charge-enhanced plasma gradient induced error in double-layer electric field measurements made by satellite double probes. Also, magnetic sheaths have been experimentally studied and compared with theory     

Chemical and Structural Evolution of Silica Alcogels During their Formation: Acoustical Study

Silica aerogels are materials of very high porosity obtained through a sol-gel process. Since their structural properties greatly influence their acoustical and mechanical properties, it is important to follow how the different chemical reactions occur during this process. We present a study of these evolutions for two different types of alcogels through acoustical measurements in the ultrasonic range. These samples have been chosen because of the significantly different behavior of the derived aerogels. The data obtained during gelation show fluctuations of the velocity that can be interpreted in terms of chemical changes. The absence of major changes in the velocity before and after gelation is explained with the aid of Biot's theory of acoustic propagation in porous media.     

Momentum transfer in collisions induced by 12C beams at intermediate energies (30–84 MeV/u)

Linear momentum transfers have been determined for C induced reactions at intermediate energies (30 to 84 MeV/u). On heavy targets, the angular correlation distributions of fission fragments indicate a limitation of the transferred momentum at 2 GeV/c in this energy range. Charged-particles emitted in coincidence with a fission fragment provide information on the prefission stage. The angular distribution of low-energy protons emitted by the heavy residues from the C + Ni reaction shows the same limitation of the transferred momentum at 2 GeV/c. Comparison of the proton and α-spectra with the results from an intranuclear cascade code including sequential cooling down of the residual partners is also given.     

The geometry of real sine-Gordon wavetrains

The characterization ofreal, N phase, quasiperiodic solutions of the sine-Gordon equation has been an open problem. In this paper we achieve this result, employing techniques of classical algebraic geometry which have not previously been exploited in the soliton literature. A significant by-product of this approach is a naturalalgebraic representation of the full complex isospectral manifolds, and an understanding of how the real isospectral manifolds are embedded. By placing the problem in this general context, these methods apply directly to all soliton equations whose multiphase solutions are related to hyperelliptic functions.Supported in part by NSF Grant No. MCS-8202288Supported in part by NSF Grant No. MCS-8002969     

Collinear laser spectroscopy techniques at JYFL

Over the last 15 years, a collinear laser spectroscopy programme has been developed at the University of Jyväskylä Accelerator Laboratory (JYFL), Finland. Continuous technique development and exploitation has taken place to address physics cases inaccessible elsewhere. In particular, the use of ion beams from the IGISOL and the pioneering application of cooled and bunched beams to laser spectroscopy. Many of these advances have additionally now been exported to facilities worldwide.     

Adsorption at cell surface and cellular uptake of silica nanoparticles with different surface chemical functionalizations: impact on cytotoxicity

Methods for the facile and in-line characterization of size distribution and physical properties of unsupported nanoparticles are of paramount importance for fundamental research and industrial applications. The state-of-the-art free nanoparticle characterization methods do not provide accuracy, high throughput, and operation easiness to support widespread use for routine characterization. In this perspective paper, we describe and discuss the opportunities provided by approaches for nanoparticle characterization based on optical measurements of the field scattered by particles. In particular, we show how insightful is the measure of both the real and the imaginary parts of the field amplitude, a task that has been considered in the past but never had a widespread exploitation. A number of opportunities are generated by this approach, in view of assessing a more efficient characterization and a better understanding of the properties of nanoparticles. We focus our attention on the capability of characterizing nanoparticles of wide interest for applications, considering cases where traditional approaches are not currently effective. Possible exploitations are both in research and in industrial environments: to validate a synthetic process, for example, or for in-line monitoring of a production plant to generate advanced process control tools, as well as decision-making tools for acting in real time during the production.     

A light-sensing knot revealed by the structure of the chromophore-binding domain of phytochrome

Phytochromes are red/far-red light photoreceptors that direct photosensory responses across the bacterial, fungal and plant kingdoms. These include photosynthetic potential and pigmentation in bacteria as well as chloroplast development and photomorphogenesis in plants. Phytochromes consist of an amino-terminal region that covalently binds a single bilin chromophore, followed by a carboxy-terminal dimerization domain that often transmits the light signal through a histidine kinase relay. Here we describe the three-dimensional structure of the chromophore-binding domain of Deinococcus radiodurans phytochrome assembled with its chromophore biliverdin in the Pr ground state. Our model, refined to 2.5 A resolution, reaffirms Cys 24 as the chromophore attachment site, locates key amino acids that form a solvent-shielded bilin-binding pocket, and reveals an unusually formed deep trefoil knot that stabilizes this region. The structure provides the first three-dimensional glimpse into the photochromic behaviour of these photoreceptors and helps to explain the evolution of higher plant phytochromes from prokaryotic precursors.